Radiation from Relativistic Electrons in Periodic Structures "RREPS-19"

15 Sept 2019, 03:00 → 20 Sept 2019, 18:00 Etc/GMT+3

Welcome to the «RREPS-19» Symposium!

  The XIII International Symposium «Radiation from Relativistic Electrons in Periodic Structures» will be held in Belgorod, Russian Federation, September 16-20, 2019, and is organized by Belgorod State University, National Research Nuclear University "MEPhI" and Tomsk Polytechnic University

The Symposium will focus on the following topics:

• General radiation properties from relativistic particles
• Cherenkov radiation
• Transition radiation
• Parametric X-ray radiation (PXR)
• Diffraction radiation and Smith-Purcell radiation
• Coherent bremsstrahlung and channelling
• Crystal-assisted processes
• Applications of monochromatic X-ray, γ-ray and Terahertz beams produced at electron accelerators

 

  We hope the Symposium «Radiation from Relativistic Electrons in Periodic Structures» will be as fruitful as the previous symposia.

Co-chairmen of		A.Potylitsyn
the Organizing Committee		A.Kubankin

Monday 16 September

08:30 Registration

09:00 Opening remarks by rector of BSU Oleg N. Polukhin

General Properties of Radiation from Relativistic Particles

1 Radiative Processes with Twisted Electrons, Photons and Neutrons

The report will provide an overview of a number of radiation processes involving
twisted particles, that is, particles with a non-zero projection of the orbital angular momentum on the direction of motion of a particle.
In this talk I review the basic properties of twisted particles and unusual properties of many atomic processes with twisted particles (new selection rules, unusual angular distribution and polarization of the final particles) which were recently considered by our Russian-German group, namely:
the Vavilov-Cherenkov radiation by twisted electrons;
radiation recombination of twisted electrons on protons;
ionization of atoms by twisted photons;
radiation recombination of twisted neutrons.
Collisions of twisted photons, electrons and neutrons may be of interest for investigations in physics of atoms, atomic and nuclear structures because they give us an additional degree of freedom: the orbital angular momentum.

Speaker: Valeriy Serbo

2 Electromagnetic Field of a Vortex Electron and Non-paraxial Effects

Vortex electrons are freely propagating particles that carry orbital angular momentum (OAM) ℓ with respect to a propagation axis and its values, obtained experimentally, already reach ℓ ~ 1000 ℏ. In contrast to the ordinary beams, such twisted electrons possess an additional magnetic moment, an electric quadrupole moment, as well as higher multipole moments. These moments can be controlled by varying the packets’ width and the OAM and can be made quite large, which influences electromagnetic field of the particles. As a result, interaction of the vortex electrons with external fields and with matter differs from that of the ordinary electrons, which may lead to relatively easily noticeable effects in electromagnetic radiation and scattering.

Here we obtain electromagnetic field of a relativistic vortex electron, described as a generalized Laguerre-Gaussian packet, in a form of a multipole expansion with an electric quadrupole term kept. The quadrupole contribution is attenuated in a paraxial regime, when the electron packet is large compared to its Compton wavelength, but it is enhanced at large OAM as well as at large times (low frequencies), when the packet’s spreading is essential. For typical parameters of the available vortex beams, the frequencies for which the contribution of the quadrupole becomes comparable to that of the magnetic moment lie below the optical part of the spectrum – in IR- and THz range. We discuss several possibilities to observe the non-paraxial effects in radiation processes due to these new multipole moments.

Speaker: Dr Dmitry Karlovets (Tomsk State University)

3 Classical and Quantum Descriptions of Radiation from Relativistic Electrons in External Fields

We review the process of photon emission by a relativistic electron moving along a classical trajectory in an external field.
In a first part we assume that the emitted photon energy is much smaller than the electron energy. This case can be treated in classical electrodynamics. We briefly review the main radiation characteristics: spontaneous or stimulated emission, dipolar or non-dipolar regime, polarization, spectral sum rules, infrared divergence, coherence length effects (e.g., LPM effect), enhancement in oriented crystals. We end up this part with some considerations on photon impact parameter, radiation damping and the side-slipping effect.
In a second part we consider the case where the photon takes a non-negligible part of the electron energy. This can happen when, in the electron frame, the external field is higher than the critical electric field $1.32$~$10^{18}$ volt/m or varies significantly in a time scale $\lambda_{Compton}/(2\pi c)=1.29 10^{-21}$ s. Then the recoil and spin effects become important and are approximately taken into account by the semi-classical formula of Baïer and Katkov (BK). We show that this formula almost coincides with an exact one when the external field is a plane wave. We state the conditions of validity of the BK formula and review its applications in high-energy coherent and incoherent electromagnetic processes in oriented crystals. Concerning the incoherent processes, we discuss whether the electron trajectory must be calculated with the classical or with the quantum scattering theory.

Speaker: Xavier Artru (CNRS)

4 Applied research at the LHEP JINR accelerator complex

Applied research planned at the accelerator complex NICA is discussed. This research includes radiobiology, material research, testing of electronic components, etc. Beam monitoring and methodology of experimetnal studies are discussed. The self-similarity approach is applied to demonstrate the attractiveness of experiments in the intermediate energy range.

Speaker: Dr Anton Baldin (LHEP JINR)

11:10 Coffe Break

5 ARIES - Accelerator Research and Innovation for European Science

oday, third- and fourth-generation synchrotron radiation (SR) sources and X-ray free-electron lasers (FEL's) find many different applications in materials science, molecular biology and biochemistry, biomedical studies, crystallography, spectroscopy, studies of rapid processes and other areas of scientific and applied research. For these applications the crucial problem consists in reaching the diffraction limit for a given beam energy of 3-6 GeV: thereby, an object can be imaged with high contrast and sharpness once its size is comparable with the wavelength of the synchrotron or undulator radiation. It was assumed that transverse emittances below 100 pm rad are necessary for the fourth generation to achieve new horizons in the research using SR. Long years it was assumed than such values of the emittance can be reached only with FEL's driven by high-brightness electron linacs. Few years ago it was demonstrated that storage synchrotrons also enable for reducing the horizontal emittance and first beams with emittances near 100 pm rad were indeed generated by the MAX-IV (Sweden) [1] and Sirius (Brazil) [2] synchrotron light sources commissioned in 2016-2017. Several similar facilities are under the design and construction stages but today's leading trend consists in upgrading the existing SR sources to fourth generation [3-7].

It is proposed that SSRS-4 complex will includes both the 6 GeV storage synchrotron and a FEL(s) [8]. Such layout leads to the complex injection system based on full-energy linear accelerator which will uses both for top-up injection into storage ring and for generation of the high-brightness drive bunches for FEL.

Speaker: Timur Kulevoy (ITEP)

6 Observation of coherent terahertz Smith-Purcell and grating transition radiation from a metasurface

We report the results of experimental and theoretical studies of coherent terahertz radiation generated by a short electron bunch from a metasurface. The metasurface is an array of sub-wavelength copper spherical-like elements placed on a monocrystalline sapphire substrate. The target has two periodicities, along and perpendicular to the electrons trajectory. Experiment was carried out using 8 MeV electron beam of KEK LUCX facility. The target was installed into 5D in-vaccuum manipulator so it could be positioned and inclined with respect to the electron beam. Because of that, several types of radiation and its properties were confirmed: Smith-Purcell radiation, Transition radiation, Grating transition radiation, Cherenkov radiation inside a substrate. The main characteristics of the radiation like spectrum, spectral-angular distribution, characteristic angle of emitted radiation, and dispersion relation were calculated. The experimental and theoretical results are compared, and good agreement is demonstrated.

Speaker: Daria Sergeeva (National Research Nuclear University MEPhI (RU))

7 Coherent effects in the ionization loss of high-energy electron bunches

Usually the ionization loss of a beam moving in substance is just a sum of independent losses of separate particles constituting the beam. In the present work it is shown that for beams (bunches) of sufficiently high particle density and small spatial size this rule can be considerably violated. In this case the value of the bunch ionization loss can exceed the above sum by several orders of magnitude. Such an effect is similar to the coherent effect in radiation by charged particle bunches. However, extremely large particle density of the bunch is required for manifestation of such an effect in thick targets, where the density effect [1] in the ionization loss takes place. But the condition on the particle density is significantly weakened if consider the ionization loss in sufficiently thin targets (or thin boundary layers of targets of arbitrary thickness), where the density effect is absent. The same holds for the ionization loss in rarefied gases with a much smaller value of the plasma frequency than in solids. In these cases the discussed effect can be manifested for bunch parameters, which are achievable at modern free-electron lasers (e. g., European XFEL [2]), and a series of accelerators presently under construction (e. g., SINBAD [3]). This effect can be of interest for the problems of charge particle beam diagnostics.
References
[1] E. Fermi, Phys. Rev. 57 (1940) 485.
[2] E. A. Schneidmiller, M. V. Yurkov, Proc. FEL 2017 Conference, Santa Fe, NM, USA, JACoW Publishing (2017) MOP033.
[3] J. Zhu, Design Study for Generating Sub-femtosecond to Femtosecond Electron Bunches for Advanced Accelerator Development at SINBAD. PhD thesis, Hamburg, 2017.

Speaker: Sergii Trofymenko (Kharkiv Institute of Physics and Technology)

8 Coherent OTR as a tool for transverse bunch size measurements

Optical Transition Radiation (OTR) is widely used for transverse beam profile diagnostics at electron linear accelerators. But this technique may not be implemented for FEL’s [1] or LWPA accelerators [2], the reason is that such machines have ultrashort bunches causing coherent effects in the OTR emission process [3]. An approach to calculate the coherent OTR (COTR) propagation through a standard optical system with a focusing lens has been developed. COTR image of the bunch profile is obtained by the summation of the OTR fields coherently emitted by all electrons from a bunch and then focused in the detector plane. Assuming the bunch transverse profile is a Gaussian type it was shown that the final image has a typical “ring” shape. The characteristics of such image depend on the bunch transverse size and can be determined from the COTR image measurement for known optical system parameters.
[1] E. Saldin, E. Schneidmiller, M. Yurkov, The Physics of Free Electron Lasers // Springer-Verlag, 2010.
[2] N. Bourgeois, et al., Transverse Beam Profile Measurements of Laser Accelerated Electrons using Coherent Optical Radiation // AIP Conf. Proc., 1507, (2012) 258.
[3] H. Loos, R. Akre, et al., Observation of Coherent Optical Transition Radiation in the LCLS Linac // SLAC-PUB-13395 (2008).

This work was supported by the grant of the Russian Ministry of Science # 3/1903.2017.

Speaker: Artem Novokshonov (DESY)

13:00 Lunch

Coherent Bremsstrahlung and Channelling

9 Channeling of Relativistic Electrons: from Basics to Applications

As known channeling of electrons in crystals can be observed for the beam energies starting from several MeV and is observable up to hudred GeV energies. Applying the same phenomenology of channeling physics for description of various behaviors of beam motion in crystals we simplify solution of many tasks that typically are split between high-energy and low-energy physics.

This report aims in reviewing recent results on channeling of relativistic electrons in crys-tals that were obtained by various groups in the world. Fine features of both electron scatter-ing in crystals and radiation by channeled electrons will be considered from the point of view of theoretical and experimental studies. Various extended applications of electron channeling for basic and applied tasks will be reported.

Speaker: Sultan Dabagov (INFN)

10 Channeling and volume reflection radiation generated by 855 MeV electrons in ultrashort Si and Ge bent crystals

The spectral intensity of gamma radiation generated by 855 MeV electrons under the conditions of channeling and volume reflection in silicon and germanium bent crystals was measured at the Mainz Mikrotron MAMI. Both crystals were 15 µm thick and bent along (111) crystal planes. Both crystals were mounted on piezo activated dynamical holder, which allowed us to change the crystal curvature online with neither vacuum braking nor any modification of the setup.

The radiation spectra were recorded for different crystal alignment, namely for channeling, volume reflection, random and “anti volume reflection”, i.e. opposite to the volume reflection direction. Moreover, this experiment was repeated for 4 different crystal curvatures for Si crystal as well as 3 curvatures for Ge. All of the experimental results were reproduced by our simulations using the CRYSTALRAD simulation code.

Radiation under the volume reflection conditions demonstrates lower but comparable radiation intensity w.r.t. the channeling case. At the same time volume reflection possesses considerably higher angular acceptance than channeling. Moreover, the volume reflection angular acceptance as well as the radiation intensity can be balanced by changing of the crystal curvature. The radiation intensity in the Ge bent crystal is roughly twice higher than in the silicon one at the equal conditions.

Speaker: Alexei Sytov (Universita e INFN, Ferrara (IT))

11 Investigation of the influence of the periodicity of crystalline atomic strings arrangement on the spectral and spectral-angular distribution of high-energy charge particle radiation in crystal

If a high-energy charged particle penetrates through a crystal having a small angle between its momentum and one of the main atomic axes, correlations between successive collisions of the particle with neighboring atoms may occur. Because of periodic arrangement in the location of atomic strings in crystal such orientational effect as planar channeling is possible. When high-energy charged particle moves in a crystal having a small angle between its momentum and one of the main crystal atomic planes the motion of particle in many cases is determined by the continuous potential of atomic planes. The existence of continuous potential leads to the planar channeling of the particle in the field of neighboring atomic planes. In this work we investigate the influence of the periodicity of crystalline atomic strings arrangement on the spectral and spectral-angular distribution of high-energy charge particle radiation in crystal.

Speaker: Dr Igor Kyryllin (National Science Center “Kharkov Institute of Physics and Technology”, Karazin Kharkov National University)

12 The Photorecombination Effect of the Ultrarelativistic Channeling Electron

Nikolay P. Kalashnikov (kalash@mephi.ru), Andrey S. Olchak (asolchak@mephi.ru)
National Research Nuclear University MEPhI
(Moscow Engineering Physics Institute).
115409 Moscow, Kashirskoye Shosse, 31, Russia
Abstract
The photorecombination process of the axial channeling high-energy electrons is considered. The photorecombination probability of an electron with radiation of the hard photon ħω and an electron transition in the channeling state with energy of the transversal motion ε_(⊥n ) is analyzed. Authors propose to use for considering of this and similar quantum electrodynamics relativistic processes the so called accompanying reference system (ARS), moving parallel to the channeling axis with the velocity, equal to the longitudinal component of the fast particle velocity, V=(p_‖ c^2)/E . In such an accompanying reference system the transversal motion of a particle, entering the single crystal at the angles, not exceeding the critical Lindhard angle θL~√(U_0/E), (where U0 is the effective depth of the axial channeling potential, E»mc2 is the relativistic energy of a penetrating particle) can be considered as non-relativistic up to the very high total energies of the incoming particles, (up to E~1011 eV for leptons). Considering the electron transversal motion with the non-relativistic energies allows employ the familiar standard results from the atomic physics. In particular the cross section calculation of the radiative recombination of electron with atomic row, which шы accompanied by the hard photon emission is presented.

Speaker: Prof. Nikolay KALASHNIKOV (NTNU MEPhI)

13 Regular and Chaotic Motion Domains in the Channeling Electron’s Phase Space and Mean Level Density for Its Transverse Motion Energy

The motion of charged particles in a crystal during axial channeling can be both regular and chaotic [1]. The chaos in quantum case manifests itself in the statistical properties of the energy level set. These properties had been studied in [2] for the electrons channeling along [110] direction of the silicon crystal, in the case when the classical motion is completely chaotic. The case of channeling along [100] direction is of special interest because the classical motion here can be both regualr and chaotic for the same energy, depending on the initial conditions.
The semiclassical energy level density as well as its part that corresponds to the regular motion domains in the phase space is computed for the 10 GeV channeling electrons and positrons. It is demonstrated that the level spacing distribution for both electrons and positrons is better described by Berry-Robnik distribution [3] than by Wigner or Poisson distributions that are related to the completely chaotic and regular situations, respectrively (see, e.g. [4]).

[1] A.I. Akhiezer, N.F. Shul’ga, V.I. Truten’, A.A. Grinenko, V.V. Syshchenko // Physics-Uspekhi 38 (1995) 1119.
[2] N. F. Shul’ga, V. V. Syshchenko, A. I. Tarnovsky, and A. Yu. Isupov, Structure of the channeling electrons wave functions under dynamical chaos conditions // Nucl. Instrum. Methods Phys. Res. B 370 (2016) 1.
[3] Berry M.V., Robnik M. // J. Phys. A 17 (1984) 2413.
[4] H.-J. Stöckmann, Quantum Chaos. An Introduction, Cambridge University Press (2000).

Speaker: Prof. Vladislav Syshchenko (Belgorod National Research University, Belgorod, Russian Federation)

14 Positron Source based on Coherent Bremsstrahlung of 10-50 MeV Electrons

Conventional positron sources are based on the conversion of bremsstrahlung from relativistic electrons into electron-positron pairs.

Reasonably effective approach for a positron source known as a “hybrid” solution [1, 2] is using a multi-GeV electron beam for production of channeling radiation (CR) in a crystalline target (radiator) with its subsequent conversion into electron-positron pairs in amorphous target (convertor).The total yields and energy spectra of positrons produced in both thin [3] and thick [4] amorphous W converters by conversion bremsstrahlung and axial channeling radiation of electrons in a thin W crystalline radiator were calculated using approach proposed in [5], revealing the advantages in the use of channeling phenomenon for getting higher positron fluxes.

On the contrary to channeling radiation from relativistic particles, coherent bremsstrahlung is characterized by higher radiation frequencies at lower energies of charged particles crossing the crystal, the radiation intensity of which exceed those for bremsstrahlung. This feature can be applied for obtaining an effective positron source at much lower electron energies. In this report we consider the radiator-converter approach for calculating total yield and energy spectra of positrons produced by bremsstrahlung and coherent bremsstrahlung (CB) using the formulae of Ref. [6] from 10-50 MeV electrons in Si and Ge crystalline radiators and W amorphous converter. Computer simulations are carried out taking into account positron stopping in a thick convert

References
1.R. Chehab, R. Cizeron, C. Sylvia et al. Physics Letters B 525 (2002) 41.
2. X. Artru, et al., Nucl. Instr. Meth. B 266 (2008) 3868.
3. S.V. Abdrashitov, O.V. Bogdanov, S.B. Dabagov, Yu.L. Pivovarov, T.A. Tukhfatullin, Nucl. Instrum. Meth. B 355 (2015) 65.
4. S.V. Abdrashitov, O.V. Bogdanov, S.B. Dabagov, Yu.L. Pivovarov, T.A. Tukhfatullin, Nucl. Instrum. Meth. B 402 (2017) 106.
5. V.A. Dolgikh, Yu.P. Kunashenko, and Yu.L. Pivovarov, Nucl. Instr. Meth. B 201 (2003) 253.
6. M. L. Ter-Mikhaelyan, Physics-Uspekhi 44(6) (2001) 571

The research was supported by RFBR (project No. 18-32-00922).

*abdsv@tpu.ru

Speaker: Sergei Abdrashitov (Tomsk Polytechnic University)

16:10 Coffe Break

Diffraction Radiation and Smith-Purcell Radiation

15 Smith-Purcell Radiation from Active Gratings

We propose the idea to drive Smith-Purcell effect by changing properties of the elements a diffraction grating consists of. The control of elements composing a diffraction grating is the idea that has already been realised in the active phase gratings, which are, e.g., integral part of modern avionics. In terms of fundamental research such gratings today are very actively investigated in the physics of metamaterials, and particularly in metasurfaces, in which they provide the attractive opportunity to control the characteristics of refracted and reflected light.
In this report we show how to control the characteristics of Smith-Purcell radiation ruling by the properties of the grating's elements and show how it can be realised by the example of the 2D dotted grating consisting of arranged small subwavelength elements. The grating considered is a metasurface comprising dot-like particles each of which is a bunch (bush) of nanotubes, imbedded into a substrate. The operation is supposed to be executed by the external electric potential, which will allow changing the electron density at the ends of nanotubes. General properties of Smith-Purcell effect are calculated and discussed.

Speaker: Alexey Tishchenko (National Research Nuclear University (MEPhI))

16 Diffraction Radiation Generation by the Internal Target of the Cyclic Accelerator

The observation and study of the properties of the diffraction radiation (DR) of relativistic electrons in the ultra-soft X-ray region ($E_{ph} \sim 100 eV$) have troubles with the usage of the extracted charge particle beam because it is necessary to establish the very small impact parameter $b\sim \gamma\lambda/2$ in the experiment. Here $b$ is the distance from the particle trajectory to the target edge,$\gamma$ is the Lorentz factor of a charged particle, $\gamma$ is the wavelength of the generated radiation. These values are for electrons with the energy of 25 MeV However, while using the target set into a cyclic accelerator [3] or a storage ring [4, 5], one can expect the enhanced yield of DR due to the multiple passages of the electron beam near the target’s edge and slow decrease of the parameter b, cycle by cycle, up to the moment of the interaction with the body of the target. During the slow transverse drawing together of the beam and the target the contribution of DR can become comparable with the contribution of the transition radiation (TR) from the target.
In this report, we compare the results of TR and DR contributions calculations, taking into account multiple passages of a charged particle near the target’s edge and experimental results presented in [4,5]. The calculations of TR and DR were performed using the theory [1,2].
This study was supported by the Federal Targeted Program of the Ministry of Education and Science of the Russian Federation agreement no. 05.575.21.0182 (RFMEFI57518X0182).
REFERENCES
[1] Potylitsyn A.P., Ryazanov M.I., Strikhanov,and Tischenko A.A. 2010 Diffraction Radiation from Relativistic Particles (Springer Tracts in Modern Physics vol 239) p278.
[2] Shevelev M, et al.,//Phys. Rev. (2015), A 92, p. 053851
[3] Kaplin V, Uglov S., Bulaev O., et al. //Nucl. Instr. and Meth. B 173 (2001) 3.
[4]. Toyosugi, N, et al.,// J. Synchrotron Rad. (2007). 14, 212–218
[5].Yamada H., et al.,//J. Synchrotron Rad. (2011). 18, 702–707
and $\gamma = 10 nm~b\cong 0.25\mu m$

Speaker: Uglov Sergey (Tomsk Polytechnic University)

17 Pre-bunched Relativistic Electron Beam Focusing by Dielectric Capillary

To date, large variety of a passive dielectric deflectors have been tested with keV electron beam for potential usage in the field of applied biology and medicine. However, there is an attraction to implement the same techniques for deflection and focusing of a low-emittance relativistic pre-bunched electron beam of a modern compact linear accelerator. To verify this possibility we have made initial experimental study at KEK LUCX facility where electron beam bunches with ps rms durations, nC charges and 8 MeV energy were transmitted through a multi-mode dielectric capillary. The 60 mm length capillary is assembled of 4 mm and 4.4 mm alternate inner diameter rings which formed a 250 um longitudinal period of the structure. The capillary is wrapped with a grounded copper tube with an internal diameter of 5.4 mm. It was shown that the shift of capillary axis parallel to the beam axis within the size of the beam cross section lead to the shift of the transmitted beam charge profile as observed at luminescent screen downstream of the capillary. At the same time, we have witnessed increase of the charge density at the screen what can be referred as a beam passive focusing by the dielectric capillary. Further investigations are foreseen to explore applicability of the given deflection/focusing scheme for femtosecond electron bunches and confirm the physics of observed phenomena.

This work was supported by the JSPS and RFBR under the Japan-Russia Research Cooperative Program (18-52-50002 YaF$\_$a), the Competitiveness enhancement program of Belgorod State University.

Speaker: Kristina Vokhmyanina (BelSU)

18 Generation of Monochromatic Radiation from a Multilayer Prismatic Target

In this report, we show the experimental results of angular distribution and spectrum of radiation produced by a multilayer prismatic target, consisting of metallic foils separated by vacuum/air gaps when an electron beam moving near target. Experiment was carried out at TPU microtron, where the 6 MeV electron beam consists of electron bunches with a repetition rate 2.63 GHz determined by RF system. We observe the sharp monochromatic lines in the spectrum of produced radiation and the dependence of the radiation intensity on the tilt angle of target. The obtained results are compared with Smith-Purcell radiation from a grating with the same period and Cherenkov radiation from a teflon prism generated for the same experimental conditions. We expect using this effects to allow increasing the monochromaticity and intensity of radiation when such a target will be designed and employed in THz and sub THz spectral ranges.

The reported study was funded by the JSPS-RFBR, project number 18-52-50002, and the Competitiveness enhancement program of Tomsk polytechnic university.

Speaker: Mikhail Shevelev (KEK)

19 Focusing of Drive and Witness Bunches in Dielectric Waveguide Filled With Inhomogeneous Plasma

Here we report the results of PIC numerical simulation of focusing of witness and drive bunches in dielectric waveguide filled with radially inhomogeneous plasma. Wakefield was excited by electron bunch in quartz (permittivity is 3.8) dielectric tube with outer and inner diameters of 1.2 mm and 1.0 mm, respectively, inserted in cylindrical metal waveguide. Energy of drive bunch electrons was 5 GeV, drive bunch charge was 3 nC, its length was 0.2 mm, bunch diameter was 0.9 mm. Witness bunch had the same parameters as drive bunch for exception of the charge equal to 0.3nC. The internal area of dielectric tube was filled by plasma with different transverse density profiles: homogeneous density, density profile created at capillary discharge, inhomogeneous radial density profile with vacuum channel along the waveguide axis. Plasma density for all considered cases was so low that the plasma frequency is less than the frequency of the main dielectric mode. The results of PIC numerical simulation show the drive bunch is focused both in homogeneous, and in inhomogeneous plasma. Acceleration and focusing of witness bunch when using inhomogeneous transverse plasma density can be improved in comparison with homogeneous plasma case.

Speaker: Prof. Gennadij Sotnikov (NSC Kharkov Institute of Physics and Technology)

18:10 Coffe Break

Poster Session

Tuesday 17 September

Cherenkov Radiation

20 Application of Cherenkov Diffraction Radiation for Charged Particle Beam Diagnostics

With over 30 000 accelerator infrastructures around the world, development of beam diagnostics has become a separate area of research in accelerator science. Such unique facilities as the Large Hadron Collider, synchrotron storage ring based light sources and X-ray free electron lasers continuously push the requirements for diagnostics equipment. These days an optimal beam monitoring devise is single shot and non-invasive providing either, detailed information about the structure of the beam or about the beam behaviour. Not all beam parameters can be diagnosed optimally these days.

During the last three years, the emission of Cherenkov Diffraction Radiation (ChDR), appearing when a relativistic charged particle moves in the vicinity of and parallel to a dielectric medium, has been investigated with the aim of providing non-invasive beam diagnostics. Our recent studies [1] of ChDR have revealed its very interesting properties including a large number of photons emitted in a narrow and well-defined solid angle, providing excellent conditions for detection with very little background. This contribution will present a collection of recent beam measurements performed at several facilities such as the Cornell Electron Storage Ring, the Accelerator Test Facility 2 at KEK, Diamond Light Source in the UK, the CLEAR test facility at CERN and the CLARA test facility in Daresbury Laboratory. Those results, complemented with simulations, suggest that the use of both incoherent and coherent emission of Cherenkov diffraction radiation could open up new beam instrumentation possibilities for relativistic charged particle beams.

[1] R. Kieffer, et al., Direct observation of incoherent Cherenkov diffraction radiation in the visible range, Physical Review Letters 121, 054802 (2018)

Speaker: Dr Karataev Pavel (Royal Holloway, Unviersity of London)

21 High-frequency radiation of relativistic charged particle bunches in presence of dielectric objects: methods and examples

Radiation of charged particles moving in presence of dielectric targets is of interests for various applications in accelerator and beam physics [1, 2]. Typically, the size of the target is much larger than the wavelengths under consideration. This fact gives us an obvious small parameter of the problem (ratio between the wavelength and the target dimension) and allows developing approximate methods of analysis. We have developed two methods: the "ray-optical method" [3, 4] and the "aperture method" [5–8]. These methods can be very effective for all situations where we can find the tangential field components on the "aperture" which is an object's boundary illuminated by Cherenkov radiation. As a rule, this cannot be done rigorously. But for high-frequency (in the aforementioned sense) radiation, this can often be done approximately.

Here we consider several new examples of the use of the developed methods. In particular, the so-called dielectric concentrator of Cherenkov radiation is studied in the situation where the charge moves parallel to the structure axis with a certain displacement from it (a problem without axial symmetry). The influence of the trajectory shift on the effect of radiation focusing is analyzed. Next, we consider the problem of radiation from a dielectric ball with a vacuum channel (the charged particle bunch moves along the channel axis). In this case, both the ray-optical method and the aperture one are used. The main analytical results are obtained. They are compared with simulations in COMSOL Multiphysics. Various physical effects are demonstrated including the effect of radiation concentration in certain small areas and the phenomenon of the "Cherenkov spotlight" in the Fraunhofer zone. Prospects for using the ray-optical and aperture methods are discussed.

The work was supported by the Russian Science Foundation (Grant No. 18-72-10137).

1. A.P. Potylitsyn et al., J. Phys.: Conf. Ser., 236, 012025.
2. R. Kieffer et al., Phys. Rev. Lett., 121, 054802.
3. E.S. Belonogaya, A. V. Tyukhtin, and S.N. Galyamin, Phys. Rev. E, 87, 043201.
4. E.S. Belonogaya, S.N. Galyamin, and A. V. Tyukhtin, J. Opt. Soc. Am. B, 32, p.649.
5. S. N. Galyamin and A.V. Tyukhtin, Phys. Rev. Lett., 113, 064802.
6. A.V. Tyukhtin, V.V. Vorobev, E.S. Belonogaya, and S.N. Galyamin, Journal of Instrumentation, 13, C02033.
7. A.V. Tyukhtin, V.V. Vorobev, S.N. Galyamin, and E.S. Belonogaya, Phys. Rev. AB, 22, 012802.
8. A.V. Tyukhtin, S.N. Galyamin, and V.V. Vorobev, Phys. Rev. A, 99, 023810.

Speaker: Prof. Andrey Tyukhtin (Saint Petersburg State University)

22 Optical Cherenkov Radiation from an Inclined Plate as a Tool for Angular Beam Diagnostics

In the paper [1] authors presented results of the measurements of the optical Cherenkov radiation generated by 255 MeV electrons passing through an inclined diamond plate with a thickness 50 micrometers. They showed that intensity of the registered photons (a part only from the whole Cherenkov cone, which is extracted into vacuum from the inclined plate) is high enough for certain detection.
We propose to use such an effect to determine a beam divergence measuring a dependence of the Cherenkov radiation yield on the inclination angle for a fixed detector position.
For electron energy ~ 1 GeV and the quartz plate thickness 4 mm it is possible to measure a divergence at the level rad.

This work was supported by the grant of the Ministry of Science of the Russian Federation (Project # 3.1903.2017).

[1] Y. Takabayashi, E.I. Fiks, Yu. L. Pivovarov, Phys. Letters A 379 (2015) 1032.

Speaker: Alexander Potylitsyn (Tomsk polytechnic university)

23 BBU Instability in Rectangular Dielectric Resonator

One of the significant limitations on the amplitude of the accelerating field in a dielectric wakefield accelerator is the head-tail drive bunch beam breakup (BBU) instability. In this report, we analytically and numerically investigate an arising and evolution of the BBU instability in a rectangular dielectric resonator when excited by a sequence of relativistic electron bunches. The dielectric resonator is a metal waveguide R26 with transverse dimensions 45x90mm with Teflon dielectric slabs (dielectric constant 2.051) with a thickness of 8.2mm located along the wide side of the resonator. The wavelength of the LM21 operating mode having a symmetric profile of the longitudinal component of the electric field is 53.2 mm. The electron energy of bunches is 4.5 MeV, the charge of each bunch is 6.4 nC, the repetition period is equal to twice the wavelength of the LM21 mode. By numerical PIC simulations, the charge losses of electron bunches on dielectric plates are investigated depending on the structure length, the initial offset of the drive bunches relative to the cavity axis. It is shown that the charge losses on dielectric slabs due to the BBU instability do not exceed 5%. When the resonance bunch repetition period is changed (a multiple of the LM21 mode's wavelength) by a period, a multiple of another eigen wavelength (e.g., the LM11 mode), the charge loss of the drive bunches does not change appreciably.

Speaker: Prof. Gennadij Sotnikov (NSC Kharkov Institute of Physics and Technology)

24 Noninvasive longitudinal beam profile diagnostic using Cherenkov diffraction radiation at CLARA facility

Production and diagnostics of short electron bunches in modern particle accelerators are forefront issues. For example, in modern X-ray free-electron lasers the electron bunches are longitudinally compressed down to <100 fs to achieve high peak currents which is crucial to drive FEL process. Such a short bunch duration opens the possibility to use effect of coherent radiation for longitudinal beam profile diagnostics. In our work we focus on using the coherent Cherenkov diffraction radiation (ChDR) effect, which is, in comparison with others types of polarization radiation has relatively high intensity, allows us to perform noninvasive diagnostic, and is highly directional providing low background detection possibility.
Experimental part was performed at CLARA accelerator [1], where a 35 MeV, 70 pQ bunch with pulse repetition rate of 10 Hz was used to produced coherent Cherenkov radiation from teflon target. Inside the vacuum chamber we developed a multi-directional manipulation platform where ChDR and transition radiation (TR) targets were mounted. It allowed us to observe both effects during one accelerator run and make relevant comparisons. For spectral analysis we used Martin-Pupplet interferometer as it provides higher signal to noise ratio and allows us to perform self-normalisation.
Theoretical part consists of calculation of Cherenkov emission from a single particle. The model we used can be found in [2], Eq. 18. It takes into account angular acceptance of optical detection line, distance between target surface and electron beam, beam energy, target dimensions and its refractive index. Using this equation with experimental parameters from CLARA we can calculate ChDR single electron spectrum to extract bunch form-factor. Longitudinal charge distribution can be obtained as an inverse Fourier transform of a square root of the form-factor [3].

As a result we will demonstrate a selection of interferograms and spectra obtained during experiments at CLARA (both for TR and ChDR targets), products of single electron spectrum calculation for specific parameters we used, and reconstructed longitudinal beam profile for CLARA machine.
References
1.P. A. Mcintosh et al., 28th Int. Linear Accelerator Conf., East Lansing, MI, USA , 734 (2016)
2.M.V. Shevelev and A.S. Konkov, J. Exp. Theor. Phys., 118: 501., 2014
3.J. S. Nodvick and D. S. Saxon, Physical Review 96, 180 (1954)

Speaker: Kirill Fedorov (RHUL)

11:00 Coffe Break

General Properties of Radiation from Relativistic Particles

25 Compton and Thomson inverse scattering as an X-ray source: state of the art and perspectives

Compton backscattering is the most promising instrument of radiation generation in the X-ray range. Comparing with modern 4-th generation facilities, Compton sources offer very important for the research laboratories advantages – relative compactness and cheapness, while the main characteristics (number of photons per pulse, energy bandwidth, pulse duration, emittance etc.) can be sufficient for applications in phase contrast and K-edge imaging, cancer therapy, computed tomography and so on. In the present report we give a short review of current state of development of such sources. We discuss the theoretical approach describing the interaction of electron beams with electromagnetic waves, advantages and disadvantages of linear and nonlinear regimes, coherent effects, polarization, as well as the progress and problems in experimental realization.

Speaker: Anastasiya Feshchenko (NRNU MEPhI)

26 Relationships between parameters of single atomic scattering and bremsstrahlung

To characterize fast charged particle scattering on an atom, two parameters are introduced, depending on the atom potential and determining the hard scattering (pre-Rutherford asymptotic behavior), and one parameter characterizing multiple scattering in atomic matter from such atoms. It is proven that the latter quantity expresses the screening momentum in the Molière’s multiple Coulomb scattering theory both in the perturbative and semi-classical regimes. For classical scattering on an atom, the existence of a scaling more general than that of Lindhard-Nielsen-Scharff is proven. A relationship between the Molière angle and the radiation length is obtained, taking into account the Coulomb nature of electron scattering on atoms in the next-to-leading logarithmic approximation.

Speaker: Dr Micola Bondarenco (NSC Kharkov Institute of Physics and Technology)

27 Conversion of Relativistic Electron Energy into One Photon when Interacting with Crystal .

N.P. Kalashnikov (kalash@mephi.ru), А.S. Olchak (asolchak@mephi.ru)
National Nuclear Research University «MEPhI» (Moscow Engineering Physics Institute)
115409 Moscow, Kashirskoe shosse, 31, Russia
Abstract
Interaction of relativistic electrons with crystal axis or plane is traditionally described in channeling model as a motion in some even, homogeneous averaged potential. However, real crystal axis or plane consists of individual atoms, positioned periodically. Interaction with periodical heterogeneities must be accompanied with quantum transition of discrete portions of momentum Δp|| = 2πnћ/d, n = 1,2,3,…, defined by the period of heterogeneities d. In axial case d is equal to the period of crystal lattice along this axis. Transmission of sufficient quantum portion of momentum to the lattice can be accompanied by the emission of photon with correspondingly high energy ћω ~ 4πћ E12/ dm2c3. In case of energies E ~ GeV or more, up to ~90% of electron’s energy may be converted into just one photon in this process.

Speaker: Prof. Nikolay Kalashnikov (NRNU MEPhI)

28 Modified Baier-Katkov Method for Twisted Photon Radiation

Nowadays the Baier-Katkov (BK) semiclassical method [1] is a standard tool to describe radiation of plane wave photons by ultrarelativistic charged particles in external electromagnetic fields of a general form. The BK method is realized in several computer codes [2,3] and proved to be very successful. We use this method to derive the radiation probability of one twisted photon [4] by an ultrarelativistic charged particle with account for the quantum recoil. In the case of negligible quantum recoil, the obtained general formula reduces to the one derived in [5].

The derived formula is used to describe the radiation of twisted photons by charged particles in undulators and laser waves. The explicit formulas for the probability to record a twisted photon are obtained in these cases. The manifestation of the blossoming out rose effect [6] in the nonlinear Compton process in a strong laser wave with circular polarization and in the wiggler radiation is revealed. Several examples are studied: the radiation of MeV twisted photons by 180 GeV electrons in the wiggler; the radiation of twisted photons by 256 MeV electrons in strong electromagnetic waves produced by the CO2 and Ti:Sa lasers; and the radiation of MeV twisted photons by 51.1 MeV electrons in the electromagnetic wave generated by the FEL with photon energy 1 keV.

References
1. V.N. Baier, V.M. Katkov, Zh. Eksp. Teor. Fiz. 55 (1968) 1542.
2. L. Bandiera, E. Bagli, V. Guidi, V.V. Tikhomirov, Nucl. Instrum. Methods B 355 (2015) 44.
3. T.N. Wistisen, A. Di Piazza, H.V. Knudsen, U.I. Uggerhoj, Nat. Commun. 9 (2018) 795.
4. U.D. Jentschura, V.G. Serbo, Phys. Rev. Lett. 106 (2011) 013001.
5. O.V. Bogdanov, P.O. Kazinski, G.Yu. Lazarenko, Phys. Rev. A 97 (2018) 033837.
6. V.G. Bagrov et al., Synchrotron Radiation Theory and its Development (World Scientific, Singapore, 1999).

Speaker: Peter Kazinski (Tomsk State University)

12:50 Lunch

General Properties of Radiation from Relativistic Particles

29 Lobachevesky space in analysis of relativistic nuclear interactions. Directed nuclear radiation - a new phenomenon.

The relativistic nature of phenomena is illustrated in terms of the Lobachevsky geometry. The Lobachevsky space is used for description of particle production in relativistic nuclear physics on the basis of experimental data obtained at bubble chambers in pi-C, p-C, C-C, n-p reactions in an energy range from units to tens of GeV. The new phenomenon - directed nuclear radiation - is discussed.

Speaker: Elina Baldina (JINR)

15:20 Coffe Break

Poster Session

Wednesday 18 September

Transition Radiation

30 Radiation of a Bunch in a Waveguide Partly Filled with an Anisotropic Dispersive Medium

In a series of works so-called reversed (backward) Cherenkov-transition radiation (RCTR) was studied [1,2]. This effect can occur when a charged particle bunch crosses the boundary between a vacuum and a left-handed medium (LHM). RCTR can be perspective for different applications in the domain of the beam diagnostics, evaluation of the medium characteristics and development of new methods of generation of gigahertz and terahertz radiation. Artificial anisotropic materials or metamaterials (MTMs) possessing left-handed properties in the GHz and THz band have been demonstrated recently (see, for example, [3-4]). In such a medium, a moving charged particle generates reversed (backward) Cherenkov radiation (RCR). The RCR can penetrate through the boundary into a vacuum and, as a result, the RCTR can be generated at some condition [5]. Here, we consider the case of waveguide loaded with the semi-infinite anisotropic MTM.
We analyze the electromagnetic field of a bunch that moves uniformly in a circular waveguide and crosses a boundary between a vacuum area and an area filled with MTM. The MTM is characterized by the diagonal dielectric permittivity tensor with components possessing frequency dispersion of plasma types. The investigation of the waveguide mode components is performed analytically and numerically with methods using as well as in papers [2, 6-7]. The cases when the bunch flies into and out of the MTM are under consideration. In compliance with the parameters of the MTM, Cherenkov radiation has direct or reversed direction in relation to the bunch motion.
In the case when the bunch flies into the MTM, intensive radiation (RCTR) can be generated in the vacuum area. The main properties of this radiation are described, and essential differences from the RCTR in the case of isotropic LHM are revealed. The analytical and numerical investigations show that the RCTR in the vacuum area always consists of a finite number of propagating modes. We show that selection of the problem parameters allows obtaining both multimode radiation and monochromatic one.

The work was supported by the Russian Science Foundation (Grant No. 18-72-10137).

[1] S. N. Galyamin and A.V. Tyukhtin, 2009 Phys. Rev. Lett. 103 194802
[2] T.Yu. Alekhina and A.V. Tyukhtin, 2018 Radiat. Phys. Chem. 145 43–49
[3] S.T. Chui, L.B. Hu, Z. Lin and L. Zhou, in Physics of Negative Refraction and Negative Index Materials, edited by K. M. Krowne and Y. Zhang (Springer-Verlag, New York, 2007), p. 75.
[4] Z. Duan, X.Tang, Z. Wang et al., 2017 Nature Communications 8 14901
[5] S. N. Galyamin and A.V. Tyukhtin, 2010 Phys. Rev. B. 81 235134
[6] T.Yu. Alekhina and A.V. Tyukhtin, 2016 J. Phys.: Conf. Series 732 012012
[7] T.Yu. Alekhina, A.V. Tyukhtin and S. N. Galyamin, 2019 Phys. Rev. Accel. Beams 22 041301

Speaker: Tatiana Alekhina (Saint Petersburg University)

31 Manifestation of the formation length effect for x-ray transition radiation by 1-6 GeV electrons in periodic multifoil radiators

Formation region effects in x-ray transition radiation are experimentally investigated. The study was performed on the test beam facility TB21 at DESY [1]. The radiation was generated by 1-6 GeV electrons in two multilayer targets of different period, which consisted of thin aluminum foils separated by air gaps. The period of the first target was smaller than the typical size of the radiation formation distance in the gap between the foils, while the period of the second one exceeded this distance. Both the effects of suppression and enhancement of x-ray transition radiation were observed at variation of the incident electron beam energy. The latter effect of radiation enhancement in the small-period radiator compared to the large-period one is a new feature of the discussed emission which was not reported in previous investigations of this kind (see, e. g., [2]). Application of this effect for a noticeable enhancement of the radiation yield is discussed and the conditions required for this are presented. The expression for the spectral density of transition radiation from a multilayer target is derived for the case of an arbitrary transversal particle distribution in the electron beam and the finite size of the detector active area. The experimental results are analyzed and compared to the theoretical estimations.
The work was partially supported by AIDA within the European Union’s Horizon 2020 research and innovation program under grant agreement No 654168.
References
[1] R. Diener et al., Nucl. Instrum. Methods Phys. Res., Sect. A 922 (2019) 265.
[2] M. L. Cherry et al., Phys. Rev. D 10 (1974) 3594.

Speaker: Sergii Trofymenko (Kharkiv Institute of Physics and Technology)

32 Effect of interference in angular distribution and new opportunities for Transition Radiation Detectors

Identification of ultra-relativistic hadrons with a good precision is a challenge for the Detector Physics. The only known way to identify multi-TeV hadrons (Pi, K and p) is using Transition Radiation Detectors. This type of detectors, however, also requires improvements to satisfy all modern requirements [1 - 3]. For that to be done, it is necessary to know all features of transition radiation. In this report we present new theoretical results concerning complex interference structure of angular distribution of transition radiation [4]. Also, recent experimental [5 – 7] results are compared with the theory and simulations in GEANT4 [8]; the latter was modified in accordance with recent theoretical and experimental results.

1. Materials of the First meeting on Small Angle Spectrometer at LHC https://indico.cern.ch/event/435373/
2. M.L. Cherry, Measuring the Lorentz factors of energetic particles with transition radiation, Nucl. Inst. and Meth. A 706, 39 (2013).
3. M.L. Cherry, G.L. Case, Compton scattered transition radiation from very high energy particles, Astroparticle Physics 18, 629 (2003).
4. A.A. Savchenko, D.Yu. Sergeeva, A.A. Tishchenko, M.N. Strikhanov, Small-angle X-ray transition radiation from multilayered structures, Phys. Rev. D 99, 016015 (2019).
5. E. Schioppa, F. Dachs, J. Alozy et al., First measurements of the spectral and angular distribution of transition radiation using a silicon pixel sensor on a Timepix3 chip, Nucl. Inst. and Meth. A 936, 523 (2019).
6. J. Alozy, N. Belyaev, M. Campbell et al., Identification of particles with Lorentz factor up to 104 with Transition Radiation Detectors based on micro-strip silicon detectors, Nucl. Inst. and Meth. A 927, 1 (2019).
7. F. Dachs, J. Alozy, N. Belyaev et al., Transition radiation measurements with a Si and a GaAs pixel sensor on a Timepix3 chip, Nucl. Inst. and Meth. A, in Press, https://doi.org/10.1016/j.nima.2019.03.092 (2019).
8. GEANT4, version 10.4, official web-sites, http://www.geant4.org/geant4/; http://geant4.web.cern.ch/geant4/

Speaker: Aleksandr Savchenko (National Research Nuclear University MEPhI (RU))

33 Application of Timepix detector for measurement of x-rays produced by a low-intensity electron beam passing through a periodic target

This report demonstrates initial testing of the high-speed spectral camera ModuPIX based Timepix detector with Si sensor. We present the first results on the measurement of x-rays produced by passing a 2 GeV low-intensity electron beam through a resonant transition radiation target and then diffracted from the HOPG crystal. A test setup was constructed on the test beam line No 21 at DESY (Hamburg, Germany). The results obtained show that the Timepix detector allows separating the low intensity diffracted X-rays from the background caused by charged particles.
The work was partially supported by AIDA project within the European Union’s Horizon 2020 research and innovation program under grant agreement No 654168 and by the Competitiveness enhancement program of the Tomsk Polytechnic University.

Speaker: Aleksey Gogolev (Tomsk Polytechnic University)

34 Monochromaticity of Transition Radiation and Diffraction Radiation from Grating

High interest in developing intense monochromatic THz sources is explained by its unique features, such as ionization absence and weak absorption in dielectric samples.
The linac at ATF KEK (Japan) can provide generation of electron bunches with length less than 0.15 mm. Therefore, it can produce THz/sub-THz radiation via coherent transition/diffraction radiation (TR/DR) mechanism. In order to produce monochromatic radiation, we investigated spectral characteristics of coherent TR/DR in the geometry where bunches interact/pass nearby with a periodical target (grating) instead of a flat metallic foil as for conventional TR/DR. As a result, a continuous spectral distribution, which is typical for TR/DR, is transformed into a spectrum with narrow spectral lines, so-called Grating Transition Radiation (GTR) [1] and Grating Diffraction Radiation (GDR).
We experimentally investigated a GTR/GDR spectral line shape for different grating tilting angle with respect to an electron beam and observed that for orientation angles much more than the inverse Lorentz factor there is some line splitting. In this report, we present spectral measurement results for two polarization components both cases and compare them with the preliminary simulation results.
This work was supported by the JSPS-RFBR grant №18-52-50002 and by the Competitiveness enhancement program of Tomsk polytechnic university.

[1] G. Naumenko, A. Aryshev, A. Potylitsyn et al. NIM B 402, 153 (2017)

Speaker: Alexander Potylitsyn (Tomsk polytechnic university)

35 Characteristics of Smith-Purcell radiation and grating transition radiation from gratings with variable profile.

In the report we compare the characteristics of the coherent Smith-Purcell radiation (SPR) and the grating transition radiation (GTR) [1] in the millimeter wavelength range generated by the 6 MeV electron beam from Tomsk microtron. The experiment was performed with the modulated electron beam with RF frequency $\gamma_0=2.63$ GHz. The measurements were carried out for two types of gratings, the first one was designed with flat strips separated by vacuum gaps with variable angles of the strip inclination, and the second one was a standard grating with a triangular profile. A sharp spectral and angular discreteness of GTR and SPR were detected. These effects are determined by the resonances between modulated beam periodicity and diffraction orders of the radiation from gratings. We demonstrate a strong dependence of the radiation intensity on the grating strip slope and its profile.

This work was supported by the JSPS-RFBR grant №18-52-50002 and by the Competitiveness enhancement program of Tomsk polytechnic university.

[1] G. Naumenko, A. Aryshev, A. Potylitsyn et al. NIM B 402 (2017) 153-156

Speaker: Dmitry Shkitov (TPU)

11:00 Coffe Break

12:00 Symposium Excursions

Thursday 19 September

Applications of Monochromatic X-ray, Gamma Ray and Terahertz Beams Produced at Electron Accelerators

36 Russian project of 4th generation synchrotron light source SSRS-4: main goals and general description

Today, third- and fourth-generation synchrotron radiation (SR) sources and X-ray free-electron lasers (FEL’s) find many different applications in materials science, molecular biology and biochemistry, biomedical studies, crystallography, spectroscopy, studies of rapid processes and other areas of scientific and applied research. For these applications the crucial problem consists in reaching the diffraction limit for a given beam energy of 3-6 GeV: thereby, an object can be imaged with high contrast and sharpness once its size is comparable with the wavelength of the synchrotron or undulator radiation. It was assumed that transverse emittances below 100 pm rad are necessary for the fourth generation to achieve new horizons in the research using SR. Long years it was assumed than such values of the emittance can be reached only with FEL’s driven by high-brightness electron linacs. Few years ago it was demonstrated that storage synchrotrons also enable for reducing the horizontal emittance and first beams with emittances near 100 pm rad were indeed generated by the MAX-IV (Sweden) [1] and Sirius (Brazil) [2] synchrotron light sources commissioned in 2016–2017. Several similar facilities are under the design and construction stages but today’s leading trend consists in upgrading the existing SR sources to fourth generation [3-7].
It is proposed that SSRS-4 complex will includes both the 6 GeV storage synchrotron and a FEL(s) [8]. Such layout leads to the complex injection system based on full-energy linear accelerator which will uses both for top-up injection into storage ring and for generation of the high-brightness drive bunches for FEL.
In this report we present current information about one of the largest Russian scientific projects. Results of the magnetic structure of the SSRS-4 main ring evolution will presented as well as the results of the beam dynamic, dynamic aperture and energy acceptance simulations. The general structure and the beam dynamics for the 6 GeV top-up injection linac will be also shown. Achievable parameters of synchrotron radiation will be discussed as well.

1 Leemann S.C., Wurtz W.A., Proc. of IPAC’17, 2017, p. 2557-2560.
2 Liu L., Westfahl-Jr. H., Towards Proc. of IPAC’17, 2017 p. 1203-1208.
3 Krinsky S., Bengtsson J., Kramer S.L., Proc. of EPAC’06, 2006, p. 3487-3489.
4 Borland M., Berenc T. G., Lindberg R.R., Sajaev V., Sun Y.P., Proc. of NAPAC’16, 2016, p. 877-880.
5 Keil J., Abs. of 2nd Workshop on Low Emittance Ring Lattice Design, 2016, p. 10.
6 Revol J.-L., Berkvens P., Biasci J. C. et al. Proc. of IPAC’13, 2013, p. 1140-1142.
7 Tanaka H., Ishikawa T., Goto S. Et al. Proc. of 7th IPAC’16, 2016, p. 2867-2870.
8 Ashanin I.A., Bashmakov Yu.A., Budkin V.A. et al. Physics of Atomic Nuclei, 2018, Vol. 81, No. 11, pp. 1646–1651.

Speaker: Sergey Polozov (MEPhI)

37 GEANT4 Modelling of Light Collection in PWO Scintillator Crystal Wrapped by a Retro-reflective Film

Scintillation light transport and collection at the entrance window of a photodetector in a great extent have effect on the energy and time resolutions of a scintillation detector, especially in the case of high value of the scintillator refraction index and its large size at least on one of dimensions. Now various wrappings are applying to improve light collection and in some cases, its linearity. To control photon capture in oblong scintillator sensors some variants of the photonic crystals are proposed [1]. As was showed [2], retro-reflector also can be successfully used for the effective control of photon transport within a detector.
In the contribution we consider distributions of scintillation photons and evaluations of energy and time resolutions in the CMS type PWO element wrapped by specular reflector (aluminum foil mirror), diffuse reflector (Tyvek), and retro-reflector (3M Scotchlite Reflective Material) irradiated by electrons and gamma-quanta with energy of 1, 10, and 100 GeV. Simulations were performed using Monte-Carlo GEANT4 toolkit supplemented by implementation of the retro-reflector into its optical simulations.

[1] M. Salomoni et al. Enhancing light extraction of inorganic scintillators using photonic crystals // Crystals 8 (2018) 78.
[2] J.W.T. Heemskerk et al. A micro-machined retro-reflector for improving light yield in ultra-high-resolution gamma cameras // Phys. Med. Biol. 54 (2009) 3003.

Speaker: Alexander Lobko (Byelorussian State University (BY))

38 Pre-bunched Electron Beam Generation and its Application for Accelerator-based THz Radiation Source

The motivation for developing of intense THz source at KEK LUCX is coming from the growing interest to THz radiation from various scientific communities worldwide. High gradient photo-cathode RF gun and few tens of femtosecond (Ti:Sa) laser system are now routinely used to generate a pre-bunched electron beam of a few hundred femtoseconds. Also, a new Yb-dopped fiber based laser system with enhanced tunability and stability is under development. We are investigating the production and properties of the intense radiation beams in the range of 0.1-0.6 THz based on Grating Diffraction Radiation (GDR) and Smith-Purcell radiation. These types of EM radiation are generated when a charged particle moves in the vicinity of a periodical pattern or grating. The grating type and period can be chosen to make quasi-monochromatic radiation spectrum. In this reports the status of the KEK LUCX facility and its RF gun laser system upgrade will be presented. Also, consequent enhancements to radiation studies will be discussed.

This work was supported by the JSPS and RFBR under the Japan-Russia Research Cooperative Program (18-52-50002 YaF$\_$a), the Competitiveness enhancement program of Tomsk Polytechnic University and the Competitiveness Programme of National Research Nuclear University ``MEPhI''.

Speaker: Alexander Aryshev (KEK)

39 Electron and X-ray source based on a pyroelectric single crystal driven by a periodically varying temperature

Nowadays, the possibilities of obtaining compact and safe particle sources and accelerators for a wide range of applications are being actively investigated and considered. One of such possibilities is a pyroelectric effect in single crystals of lithium niobate (LiNbO$_{3}$) and lithium tantalate (LiTaO$_{3}$) can lead to acceleration of electrons to energies of the order of 100 keV and to generation X-rays with broad spectrum. However, electric breakdowns prevent stable particles acceleration.
The sinusoidal mode of changing the temperature of a pyroelectric single crystal leads to oscillations the pyroelectric current with a typical frequency of the order of 1-50 mHz and the amplitude of about 1-10 nA for samples with area of several cm$^{2}$. In vacuum condition that current might induce high electric field, which oscillates with the same frequency. Estimated amplitude of electric field is of the order of $10^{5}$ V/cm.
The possibilities and the advantages of using such mode of temperature change to obtain a quasi-stable X-ray and electron pyroelectric source are considered. Preliminary results of measurement of electron and X-ray flux are reported.

Speaker: Andrey Oleinik (Royal Holloway College, University of London \ Belgorod State University)

40 Dose-Enhancing Agent for Radiotherapy at 6 and 10 MV Medical Linac

Radiation therapy is an important and effective technique of malignant tumors treatment [1]. Actual problem of radiotherapy is increasing effectiveness and reducing side effects of the treatment. Binary technologies of radiation therapy can be used to improve treatment results. One of the most promising technology is contrast-enhanced or “photon-capture” radiotherapy (PCT) [2]. The PCT is effective at low X-ray energies where the photoelectric effect dominates (up to about 200 keV). Accordingly, the energy escalation of photon beams leads to a gradual decrease the effect of the PCT. However, low-energy photons for medium- and deep-seated tumors are limited due to their low penetrating power. For irradiation of deep-seated tumours, the megavoltage photon beams from linear accelerators are widely used, where the Compton effect is maximal and the photoelectric effect is minimal.
Although the effect of PCT should be low, different studies shows the escalation of energy in the target volume due to the introduction of dose-enhancing agent (DEA) at megavolt photon beams [4-6]. Some authors suggest that the observed effect is caused by the wide energy spectrum of photon beams, which including the low-energy kilovolt energy range.
In this research we simulated the dependence of dose increase on the DEA concentration at 6 and 10 MV medical Linac using Monte-Carlo simulation by the means of Geant4.

References:
1. R. Baskar, K.A. Lee, R.Yeo, et al. Cancer and Radiation Therapy: Current Advances and Future Directions //International Journal of Medical Sciences. V.9(3), P.193–199.
2. I.N. Sheino, P.V. Izhevskij, A.A. Lipengolts, et al. Development of binary technologies of radiotherapy of malignant neoplasms: condition and problems //Bulletin of Siberian Medicine. 2017. V.16(3). P.192-209.
3. Jain S. Coulter JA. Hounsell AR. et al. Cell-specific radiosensitization by gold nanoparticles at megavoltage radiation energies //Int J Radiat Oncol Biol Phys. 2010. V.79. P.531–9.
4. D. Chithrani, S. Jelveh, F. Jalali, et al. Gold nanoparticles as radiation sensitizers in cancer therapy //Radiat Res. 2010. V.173. P.719–28.
5. R. Berbeco. H. Korideck. W. Ngwa, et al. TU‐C‐BRB‐11: In Vitro Dose Enhancement from Gold Nanoparticles under Different Clinical MV Photon Beam Configurations //AAPM. 2012. V.39(6). P. 3900-3901.

Speaker: Anatoly Baulin (TPU)

10:50 Coffe Break

Applications of Monochromatic X-ray, Gamma Ray and Terahertz Beams Produced at Electron Accelerators

41 Measurement of Wide-Aperture X-ray Beam Trasverse Profile Based on Multiangular Wire Scanning

Nowadays radiation sources are widely used in different investigations and technological applications, such as radiation therapy, sterilization of medical equipment, welding, microstructuring processes etc. It is necessary to control beam parameters in exploitation of devices designed for this purposes. One of the main parameter is the particle flux density distribution in a transverse plane of the beam.
Previously we suggested a new method for particle flux density distribution in a transverse plane of the beam. The method is based on mathematical reconstruction of experimental data, which is observed multiple beam scanning by thin strip under different angles.
In this work these method is tested experimentally. In the experiment, an X-ray tube is used as a radiation source, while thin scintillation strip as a sensitive scanning detector. In this strip, light photons is generated due to interaction with X-ray beam. These photons is guided by optical fiber to the photomultiplier. Scintillation strip moves in the plane, which is perpendicular to the beam propagation. Thus, we experimentally observe a set of registered photons intensity on strip location and angle orientation with particular angle step. These dependences is further used to reconstruct particle flux density distribution in a transverse plane of the beam.

Speaker: Dr Sergei Stuchebrov (National Research Tomsk Polytechnic University)

42 Self-amplification of Radiation from an Electron Bunch Inside a Waveguide Filled with Periodic Medium

We investigate the radiation from a bunch of relativistic electrons moving along the cylindrical waveguide axis, assuming that a part of the waveguide is filled with a layered material, the dielectric permittivity and magnetic permeability of which are arbitrary periodic functions. Analytical expression is provided for the spectral distribution of the radiation energy flux through the cross section of the waveguide at large distances from the layered medium. It is based on the corresponding exact solution of Maxwell equations for the case of a single electron moving along the waveguide axis. The results of numerical calculations are presented in the special case of layered medium consisting a finite number of dielectric plates separated by vacuum gaps. We show that under certain conditions on the problem parameters, the quasi-coherent Cherenkov radiation generated by the electron bunch inside the plates is self-amplified at certain waveguide modes. A visual explanation of this phenomenon is provided. We also present a simplified model that reproduces with satisfactory accuracy the main features of the self-amplification phenomenon. The possibility of using this phenomenon to develop powerful radiation sources in the terahertz frequency range is discussed.

Speaker: Prof. Levon Grigoryan (Institute of Applied Problems of Physics NAS RA)

43 2D Focusing of Reflected Hard X-Rays and Thermal Neutron Beams in the Presence of External Temperature Gradient

It was experimentally shown that in the presence of temperature gradient in X-cut quartz crystal it was possible to obtain 2D bending of reflecting atomic planes (10-11) depending on the position and shape of heater, thereby ensure the possibility of 2D focusing of X-rays at reflection from these planes. It is noteworthy that the degree of bending depends on the thermal expansion coefficient in the given direction. Consequently, in case of appropriate choice of crystal, of its cut and the family of reflecting atomic planes, one can provide such a 2D bending, at which a point focus of reflected X-ray radiation is obtained. It is also shown that under these conditions the integrated intensity of reflected X-ray radiation increases by several orders of magnitude, and the angular width in mutually perpendicular directions is controllable.
Reflection of thermal neutrons beam from the quartz crystal in the Laue geometry under the external influences was investigated theoretically. The possibilities and estimation of the time-spatial control of thermal neutrons beam parameters (relative maximum intensity, angular and energy distributions of receiving beams, etc.) are analyzed.

This work was supported by the RA MES State Committee of Science, in the frames of the research project № 18T-1C395, and by the RA MES State Committee of Science and Russian Foundation for Basic Research (RF) in the frames of the joint research project SCS 18RF-142 and RFBR 18-52-05024 Arm_a accordingly.

Speaker: Vahan Kocharyan (Institute of Applied Problems of Physics of NAS RA)

44 Investigation of the Interaction of Ion Beams with Deuterated Crystal Structures at the HELIS Facility

The results of studies of the interaction of ion beams with deuterated crystal structures at the HELIS facility (LPI) are presented. In DD-reactions in deuterated crystal structures at deuteron energies 10-25 keV, significant enhancement effects are observed. For CVD-diamond and Pd targets, the orientation of the sample with respect to the deuteron beam was shown to affect the neutron yield.

Speaker: Dr Mikhail Negodaev (P.N. Lebedev Physical Institute RAS)

12:30 Lunch

Applications of Monochromatic X-ray, Gamma Ray and Terahertz Beams Produced at Electron Accelerators

45 Piezoelectric Transformer for Generation of X-rays in Vacuum

Results of experiments on the electron acceleration and X-ray generation in during operation of the piezoelectric transformer in vacuum are described here. Piezoelectric transformer operates at the resonance frequency. Electrons are accelerated from the high voltage electrode of the piezoelectric ceramic transformer to the grounded target, which leads to generation of the characteristic and bremsstrahlung x-ray. The returning of the charge to the high-voltage electrode is provided due to electrons emitted from a filament installed near the target. We found that the X-ray yield increases linearly at increasing of the pressure of the residual gas in the chamber within two orders of magnitude up to about ten mTorr, when the gas discharge around of the piezoelectric transformer arises. Possible applications of the piezoelectric transformer for production x-ray in the miniature accelerators are discussed. In this work, the last results of the measurements x-ray spectra are presented.

Speaker: Oleg Ivashchuk (Belgorod State University)

46 Adaptive X-ray Optical Elements Based on Longitudinal and Transverse Acoustic Waves in the KHz and MHz Frequency Ranges

X-ray acoustic interactions allowing to implement the control of X-ray parameters are widely studied. Among the numerous researches, it is possible to highlight the ability of controlling the spatial and energy spectrum of X-ray radiation [1] and the effect of redistribution of intensity between transmitted and diffracted beam [2]. This paper describes the implementation of a combination of these two possibilities.
Fast control of X-ray parameters, including scanning diffraction conditions and controlling by times much shorter than possibilities of traditional approaches, is a very relevant scientific task. It will be shown that overcoming of limitation of traditional approach, such as complex goniometric systems, possible by using of non-mechanical adaptive X-ray optic elements, such as X-ray acoustic resonators of longitudinal oscillations or bimorph piezo-actuators. It allows fast and precise variation of X-ray diffraction parameters, varying the angular position of the X-ray beam and controlling its wavelength. Description of schemes and elements for fast tuning of beam parameters will be given.
The effects of the redistribution of intensities between the diffracted and transmitted X-ray beams under the conditions of excitation of resonant acoustic thickness oscillations in quartz crystals were investigated. It has been established that the effect of increasing the intensity of a diffracted beam almost linearly depends on the amplitude of ultrasound (the FWHM of the rocking curves does not change at the same time) and is observed for all the studied reflexes.
The time characteristics of the observed effects upon excitation and relaxation of ultrasonic oscillations were investigated for the first time: the process of increasing intensity takes about 250 microseconds, then its oscillation is observed for about 1 millisecond, and the process of complete relaxation takes about 1.5 milliseconds.
Preliminary design of elements combining thickness and longitudinal oscillations are considered, several schemes of implementation are proposed. The effect of intensity redistribution in Potassium and Rubidium hydrogen phthalate crystals, which are emerging materials for creating a two-frequency element, was studied for the first time.
Prospects of implementation of such methods and elements at synchrotron radiation as well as laboratory sources will be discussed.
The reported study was partially supported in the framework of the joint programs of the Russian Foundation for Basic Research (project № 18-52-05024 Arm_a and №18-32-20108 mol_a_ved) and Science Committee of Ministry of Education and Science of Armenia (project №18RF-142) as well as the Council on Grants of the President of the Russian Federation МК-2451.2018.2.

1. A.E. Blagov, M.V. Kovalchuk et al. JETP letters, t.128, 5 (11) (2005). P.893
2. A.P. Mkrtchyan, M.A. Navasardyan, V.K. Mirzoyan. JTP letters, 8, 677 (1982)

Speaker: A.V. Targonskiy (FSRC “Crystallography and photonics” RAS, NRC “Kurchatov institute”, Moscow, Russia)

Crystal-assisted Processes

47 Recent advances of crystal channeling in accelerating science.

A.G. Afonin, M.Yu.Chesnokov, Yu.A.Chesnokov, V.A.Maisheev, A.A.Yanovich,
Institute for High-Energy Physics (IHEP) in National Research Center “Kurchatov Institute”,
Protvino, Moscow region, 142281 Russia

Ideas of use the particle channeling in bent crystals for steer the beams have been checked up and advanced in many experiments. Recently, a curved single crystal was tested at the LHC for the task of the beam collimation [1]. This method is also widely used in U-70 accelerator of IHEP, where crystals are used in regular runs for beam extraction and forming [2]. However, until now, this method of beam formation has limitations in application, since the channeling process involves beam particles with low angular divergence, limited by the angle of Lindhardt (it is equal to 25 microradians for the energy of the Protvino accelerator U-70 for 70 GeV). Here we describe two crystal devices, the focusing crystals and multistripe crystals, which expand the boundaries of application of bent crystals at accelerators. The created focusing crystal [3] reveal the possibility of a new optics of the beams for extremely high energies. Modern accelerators go into the TeV Energy region, the LHC is already operating at 6.5 TeV. The FCC and SPPC with energies up to 100 TeV are planned. In this region of energies, the scattering of secondary particles from the targets is very narrow, a fraction of milliradian. We propose special crystal elements with a focusing edge for the formation of particle beams of such energies. These crystals can work as super-strong lenses with a focal length of about 1m, with an equivalent magnetic field of 1000 Tesla. The proposed ideas are supported by experimental studies on the U-70. Multistrip crystals [4] are also created, which can deflect beams of positively and negatively charged particles due to the phenomenon of reflection from curved atomic planes by more than 90% efficiency. These devices are promising for radiation-protection septum SM24 and collimation of the proton beam crystals in a magnetic block 86 accelerator U-70. Also, multilayer crystal structures can be used to protect the electrostatic septum of the SPS accelerator at CERN [5], for which the corresponding calculations will be carried out using the proposed algorithm.
References.

[1] W.Scandale et al, Phys.Lett., B758, (2016), 129
[2] A.G.Afonin et al, International Journal of Modern Physics A 33, (2018) 1850138
[3] G.I.Britvich et al, JETP, in press
[4] A. G. Afonin et al , Phys.Rev. AB 22, 033001 (2019)
[5] F.M. Velotti, P. Bestmann, M. Butcher et al, IPAC-2019

Speaker: Yury Chesnokov (Institute for High Energy Physics of NRC Kurchatov Institute (R)

48 MEASUREMENTS OF CHARGE OF PARTICLES BY A SEMICONDUCTOR DETECTOR

Usually, magnetic field is used for identification of different accelerated particles. This method is sensitive to the relation Z/M, where Z and M are the charge and mass of the particles respectively. Here, we propose to apply measurements of ionization loss that depends mainly on Z for identification of particles. Recently, we observed carbon ions +6C and its fragments with Z=1,2,3,4,5 of energy 25 GeV/nucleon by Si surface-barrier detector of size 10*10 mm and thickness of the depleted layer 300 mkm at accelerator U-70 [1,2]. The measured spectrum of ionization loss, shown in figs. 8 in both papers [1,2], contains 6 corresponding Landau spectral peaks at different energies depending on the charge of particles. The measurements of ionization loss together with application of magnetic field can be used for identification of particles in a beam that contains different particles.

References
[1] A.G. Afonin, E.V. Barnov, G.I. Britvich, A.A. Durum, M.Yu. Kostina, V.A. Maisheev, V.I. Pitalev, S.F. Reshetnikov, Yu.A. Chesnokov, P.N. Chirkov, A.A. Yanovich, R.M. Nazhmudinov, A.S. Kubankin, A.V. Shchagin. Extraction of the carbon ion beam from the U-70 accelerator into beamline 4a using a bent single crystal. Instruments and Experimental Techniques 59(4) (2016) 497-500.
[2] A.G. Afonin, E.V. Barnov, G.I. Britvich, Yu.A. Chesnokov, P.N. Chirkov, A.A. Durum, M.Yu. Kostin, V.A. Maisheev, V.I. Pitalev, S.F. Reshetnikov, A.A. Yanovich, R.M. Nazhmudinov, A.S. Kubankin and A.V. Shchagin. The measurement results of carbon ion beam structure extracted by bent crystal from U-70 accelerator. Journal of Physics: Conference Series 732 (2016) 012027.

Speaker: Alexander Shchagin (Kharkov Institute of Physics and Technology)

49 Possible method of spatial sizes measurement of relativistic electrons beam with small longitudinal bunch length

Possibility of practical realization suggested earlier methodic of electron beam sizes determination for electron bunches with short length by measurement of two-dimensional angular distributions of relativistic electrons coherent emission in a crystal for two distances between a crystal, where the radiation is born, and a coordinate detector [1] is analyzed. As an emission source the diffracted transition radiation is used. The minimum measured beam size is about 10--15 microns for electrons with energy above several GeV. The technique is weakly sensitive to pulse heating of the target if it does not destroy the crystal, and can be used on intense beams of linear accelerators creating x-ray free-electron lasers [2]. Influences of secondary electrons and photons outlet from a coordinate detector and the method applicability for different longitudinal bunch length are discussed. The limits of the technique applicability and sensitivity are presented.

References
1. I.E. Vnukov et al., // J. Surf. Invest.: X-ray Synch. Neutron Tech. 13 (2019) 515.
2. The European X-Ray Free-Electron Laser Technical Design Report, DESY 2006-097, 2007.

Speaker: Prof. Igor Vnukov (Belgorod National Research University)

15:40 Coffe Break

Crystal-assisted Processes

50 APPLICATION OF SEMICONDUCTOR DETECTORS WITH SMOOTHLY TUNABLE THICKNESS IN SPACE TELESCOPE OF RELATIVISTIC CHARGED PARTICLES

Space telescopes of charged particles consist of stack of Si detectors and are intended for measurements of energy and direction of motion the particles. The detectors are as Si slabs supplied by permanent bias voltage [1]. We proposed [2] application of Si detectors with smoothly varying by the bias voltage thickness of the depleted zone in the telescope. The application of such detectors would allow optimize operation of the space telescope without any mechanical motions.
For instance, 1.6 mm thick beryllium slab is installed before the first detector of the telescope for absorption of low-energy particles [1]. The slab provides fixed energy threshold for incident particles. Instead of beryllium slab, we propose to install the first Si detector with depleted zone turned toward the telescope. Regulating bias voltage, one can simultaneously change the thickness of the depleted zone and the thickness of non-sensitive Si layer, where charge is not collected from. Thus, one can smoothly regulate the thickness of absorbing layer and register passed particles in depleted zone of the same first detector. This means that the energy threshold at observation of charged particles can be variated smoothly, that is impossible with the beryllium slab.
Si detectors with variable thicknesses were studied in our researches with electrons of energy < 1 MeV in KIPT [3] and 50 GeV protons at accelerator U-70 [4].

References
[1] D.N. Baker et al. Space Science Reviews 179 (2017) 337–381.
[2] A.V. Shchagin. Semiconductor detectors with smoothly tunable thickness in space relativistic electron-proton telescope. Theses of reports at XVII conference on high energy physics and nuclear physics, 26-29 March 2019, KIPT, Kharkov, Ukraine, p. 103-104. The thesis is available in English in page 103 at:
https://www.kipt.kharkov.ua/conferences/ihepnp/2019/collection_of_theses_%D0%A5VII_hepnp.pdf
[3] A.V. Shchagin, N.F. Shul’ga, S.V. Trofymenko, R.M. Nazhmudinov, A.S. Kubankin. Semiconductor detector with smoothly tunable effective thickness for the study of ionization loss by moderately relativistic electrons. Nucl. Instrum. Methods B 387 (2016) 29–33.
[4] R.M. Nazhmudinov, A.S. Kubankin, A.V. Shchagin, N.F. Shul’ga, S.V. Trofymenko, G.I. Britvich, A.A. Durum, M.Yu. Kostin, V.A. Maisheev, Yu.A. Chesnokov, A.A. Yanovich. Study of 50 GeV proton ionization loss by semiconductor detector with smoothly tunable thickness. Nucl. Instrum. Methods B 391 (2017) 69–72.

Speaker: Dr Alexander Shchagin (Kharkov Institute of Physics and Technology)

51 Scintillation Signal Strong Enhancement in an Axially Oriented Lead Tungstate Crystal

The interaction between a 120 GeV/c electron beam and a 4 mm thick lead tungstate scintillator was investigated at H4 beamline of SPS, in CERN North Area. The high Z target material was chosen in order to provide intense fields (E≈10^11 V/cm). In the beam rest frame, the internal electric fields are enhanced by a Lorentz factor. Thus, the effective field perceived by electrons exceeded Schwinger critical field limit (E0≈1.32x10^16 V/cm). In this condition, the electromagnetic shower process is supposed to be accelerated inside the medium. In this experiment, evidences of faster shower development were probed by measurements of the scintillation light produced by the crystal. A reflective coating was applied to the sample, a SiPM was coupled to the base of the sample to collect signal intensity. Measures were performed in condition of alignment with [001] axis and in condition on misalignment with major crystallographic axes and planes. A clear enhancement of scintillation light intensity was measured in case of axial alignment. This effect could prove of great interest for future electromagnetic calorimeters with improved features of signal intensity and maximum measurable energy, provided a flux of incoming particles with small angular spread (i.e. forward physics, astrophysics sources)

Speaker: Marco Romagnoni (Universita e INFN, Ferrara (IT))

52 Manufacturing of Silicon Crystals for Steering of Ultra-High Energy Particle Beams

Physics of interaction between X-rays or gamma beams and crystals have been worldwide investigated at synchrotron where electrons with energy from tens of MeV to few GeV circulating in storage rings produces X-ray beams which are delivered to extracted lines.
Since the ’70, physics of interaction between bent crystals and heavy particles (protons or ions) is investigated at various worldwide particle accelerators, driven by the possibility to use bent crystals as optical elements for steering or focusing charged particle beams. Recent developments in crystal manufacturing, joined with a deeper understanding of the physics behind crystals-particle beams interaction lead to a discovery of numerous interactional effects.
Nowadays technology readiness level is mature enough to allow the use of crystals even in the Large Hadron Collider (LHC) of CERN, where crystals are being experimented as primary collimators of the protons or ions circulating beam and are suggested as core elements of fixed-target experiments. Given the extremely high intensity and energy reached in modern accelerators or in future planned ones (such as FCC, ILC, CLIC and CEPC), implementation of bent crystals at such facilities demands to face with various technological challenges.
In this contribution we describe manufacturing and characterization of crystals suitable for installation in the LHC as primary collimators of circulating beams. Successful development of such crystals is based on a merging of ultra-modern technologies used in microelectronics, X-ray science, ultra-precise optical and mechanical machining.

Speaker: andrea mazzolari (INFN Ferrara)

53 Angular anisotropy of multiple scattering in a crystal

Multiple Coulomb scattering in a crystal is anisotropic due to the presence of the coherent part in the Coulomb scattering cross section. This part depends on the crystal alignment and can be either increased or suppressed by the choice of the crystal alignment. As the result, the r.m.s. multiple scattering angle depends on the crystal orientation.

For the investigation of this process the experiment on Coulomb scattering of 855 MeV electrons was conducted at the Mainzer Mikrotron MAMI. Crystalline and amorphous silicon membranes both with a thickness of ~34 µm were used as targets. Multiple scattering angle was measured for the alignment of complete coherent scattering suppression, predicted by our model, as well as in a wide angular range. The experimental results were critically compared with our simulations and theoretical predictions.

We report the observation of the reduction of multiple Coulomb scattering in a crystal in comparison with the amorphous target. We demonstrate the maximal 7 % reduction of the r.m.s. multiple scattering angle at certain crystal alignment with the [100] crystal axes and partial reduction in a wide range of angles of alignment up to 15 degrees. Moreover, we observe the opposite effect, i.e. the increase of multiple Coulomb scattering at the orientation nearly parallel to the skew crystal planes.

Speaker: Alexei Sytov (Universita e INFN, Ferrara (IT))

19:00 Symposium Dinner

Friday 20 September

Parametric X-ray Radiation

54 Dynamical effect of asymmetry in the parametric X-rays radiation generated by relativistic electrons in a single-crystal target

The dynamic theory of coherent X-rays of a relativistic electron crossing a single-crystal target in the Laue scattering geometry is discussed. In [1] Expressions describing the spectral-angular characteristics of radiation in the direction of Bragg scattering are obtained and investigated by the author of the present work. The radiation is considered as a result of coherent addition of the contributions of two radiation mechanisms parametric X-ray (PXR) and diffracted transitional (DTR). The calculations showed that in the case when the diffracting atomic planes in the target are located relative to the target surface at an angle of, a noticeable difference is observed in the results of the calculation of the spectral-angular density of the PXR within the dynamical theory and the kinematical one (reflection asymmetry effect). The analysis showed that the main cause of this effect is the absent in the kinematic theory of the dependence of the width of the PRI spectrum on the asymmetry angle. In [2], good agreement between the developed dynamic theory and experiment [3], which was carried out under conditions of asymmetric reflection of the Coulomb field of an electron on a single-crystal target, was shown.
1.S.V. Blazhevich, G.A. Grazhdankin, R.A. Zagorodnyuk, A.V. Noskov //Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, Volume 355, 15 July 2015, Pages 170-174.
2.S.V. Blazhevich, A.V. Noskov, //Nuclear Inst, and Methods in Physics Research B 441 (2019) 119.
3.Y. Takabayashi, K.B. Korotchenko, Yu.L. Pivovarov, T.A. Tukhfatullin, //Nucl. Instr. Meth. B 402 (2017) 79.

Speaker: Prof. Sergey Blazhevich (Belgorod state university )

55 Diffraction of real and virtual photons in crystalline powders

The distance between crystallographic planes is of the same order as the X-ray wavelength. For this reason, crystals act as diffraction gratings for X-ray [1]. This interaction is referred as diffraction of real photons. On the other hand, Parametric X-ray Radiation (PXR) has been described as the diffraction of the charged particle Coulomb field in the crystal. This mechanism is referred as diffraction of pseudo, virtual or equivalent photons [2].
This experimental work presents the measurements of signals produced during the interaction of both 7 MeV electrons and X-rays with tungsten powders. The measurements correspond to the diffraction of virtual and real photons respectively. Tungsten powders were chosen because in the energy region between 2 and 7 keV the diffracted peaks from five crystallographic planes can be analysed without the influence of background peaks. The characteristics of both diffraction processes are analysed and compared. Parameters such diffraction peak yield, peak FWHM and peak to background ratio are discussed.
The work was supported by scholarship of the President of the Russian Federation for young scientists and graduate students SP-765.2019.2 and by project PIJ-16-03 of the Escuela Politécnica Nacional.
References
[1] R. James. The Optical Principles of the Diffraction of X-rays. (1948).
[2] X. Artru, P. Rullhusen. Nucl. Inst. Meth. B 145 (1998) 1-7.

Speakers: Esteban Irribarra (Escuela Politécnica Nacional), Ramazan Nazhmudinov (Belgorod National Research University)

SUMMARIES

56 “RREPS-19” Proceedings publication

Speaker: Pavel Karataev (Royal Holloway, University of London)

11:40 Coffe Break