CLIC Meetings 2008

We present highlights from our visit to KEK/ATF in December 2007, including ATF beam studies, the ILC-Damping Ring workshop, and the 5th ATF2 Project meeting.

The need for high accelerating gradient for CLIC imposes considerable constraints on the materials of the accelerating structures. The surfaces exposed to high pulsed RF currents are subject to cyclic thermal stresses possibly resulting in surface break-up by fatigue. Since "CLIC compatible" fatigue data does not exist in the literature, a comprehensive study was initiated. It is also likely that pure oxygen-free copper cannot meet the current CLIC parameters so a set of candidate materials were studied. A combination of three independent fatigue experiments are hoped to enable quantitative predictions for the required 20 years lifetime of the CLIC accelerating structures.

We present the status of the CTF3 Combiner Ring commissioning with the main focus on the optics measurements: tune, dispersion, response matrix, and closed orbit length.

The 8 GeV C-band electron linear accelerator is under construction at the SPring-8 site aiming at generating an FEL X-ray beam in 2010. C-band accelerator technology has been developed initially at KEK for the e+e- linear collider project, and employed at the XFEL project in Japan. Since C-band generates a high gradient acceleration field as high as 35 MV/m, the total length of the accelerator fits within 400 m, including the injector and three bunch compressors.
XFEL requires precise control of the rf intensity and phase for electron bunch compression. We know the largest source of the pulse-to-pulse instability (jitter) is the klystron voltage jitter. Therefore, we have been developed extremely stable klystron power supply.
The talk will cover the current status of the XFEL project and hardware development, focused on the klystron power supply.

The results of last years high-gradient experiments will be presented and summarized. The focus will be on 30 GHz results obtained in CTF3 but the experiments at SLAC will be mentioned as well.
Jan will present first results of his time resolved spectrometer and Alexey will review the improvements of the automatic conditioning system and the conditioning website. 

The observations made for structures tested last year will be presented. They concern the two disc structures pi/2 and 2pi/3 after test. Also observations on 30HDS thick structure before and after RF test will be presented, including the effects of chemical cleaning and heat treatment preparation for a new RF test. For 30CNSQ thick and 30HDS11 small structures only the characterization before testing will be shown.

Intrinsic and dynamic outgassing from beam pipe materials hinders the achievement of very low pressure. Both surfaces and bulk contributes to the total gas load that must be evacuated by appropriate and expensive pumps. To reduce this inconvenience, two lines of attack are generally considered: surface modification, either by chemical methods or coating, and thermal treatments. After a summary of the most prominent features of outgassing, I will focus the talk on chemical cleaning methods and on the main approaches for the evaluation of cleanliness. Thermal treatments, both in vacuum and in air, will be considered and the main equations for the evaluation of outgassing rate variation will be addressed. The benefits of coating will be underlined, in particular for NEG, and their limitations critically analyzed, mostly for polymeric substrates. Finally, I will elaborate on some subjects of  specific interest for the CLIC project regarding surface treatments and characterisation (for example low SEY materials, low activation temperature NEG, water outgassing in the RF cells, electropolishing, etc.).

After a consolidation phase that lasted several months, PLACET has reached its maturity. Also, its diffusion among several institutes improved portability, usability and reliability of the code. Several PLACET based studies are ongoing: study of the emittance growth in the CLIC Injector and the Booster Linacs, beam-based alignment of the CLIC Beam Delivery System, feedback system and static alignment of the ATF2 machine, start-to-end simulations of fast intratrain feedback in ILC, and crab cavity correction schemes in the ILC BDS. In this talk some of these results will be reviewed.

A short prototype of the SC wiggler for the CLIC damping ring is now under production at BINP, Novosibirsk.  In this report we describe the wiggler parameters, present status, magnetic measurement approach and time schedule. The problem of the SR power evacuation from the wiggler straight section (including software and illustrative results) is discussed.

Comprehensive analysis of high gradient  RF test results both at X-band and at 30 GHz will be given. An analytical model of  RF breakdown will be described.  A new  RF field quantity will be defined, which limits high gradient perfomance of accelerating structures. Implications for CLIC main linac accelerating structure design will be discussed.

The CTF3 tail-clipper must have a rise-time of 5ns or less in order to minimize uncontrolled beam loss; this is a technically challenging requirement. This talk reviews the design of the tail-clipper, presents measurement data and gives an update of the status of this fast kicker. 

The tailclipper collimator in the TL2 transfer line will have a double functionality. At first, it will serve, in combination with the tail-clipper kicker, to adjust the bunch train length arriving from the combiner ring. In addition, when required, it will operate as an internal beam dump. The need of combining these two functionalities together with the beam parameters imposes strict constraints on the design of the collimator. This presentation will cover the design of the Tailclipper collimator, the key issues during its operation and the status of the production.

The stabilization working group reports to the newly created CLIC Technical Committee. It regroups the labs collaborating on the subject. The first Stabilization day held in March was the opportunity to review the state-of-the-art and to elaborate a work plan in order to demonstrate the feasibility. This presentation will give hints on what's going-on and what we could expect to achieve in the next years.

Two photoinjectors are presently under construction at CERN. One of them will be the source of the CALIFES probe beam in CLEX, the other one is part of the PHIN joint research activity in CARE. The PHIN photoinjector is being installed on a stand-alone test bench in CTF2. The electron bunches in both photoinjectors are produced by illuminating Cs-Te photocathodes with energetic pulses of UV laser light. The laser system is, to a large extent, common to both photoinjectors. Preparation of photocathodes takes place "in situ" for the CALIFES photoinjector, while the photocathodes for PHIN are produced in the laboratory and transported to the photoinjector under vacuum.
In this CLIC meeting, the construction- and installation-status of the two RF guns is summarised. The present performance of the laser system is described in detail, and the status of the photocathode production is given.

The seminar will address the role of calorimetry at CLIC. Using the reports made at the EFCA linear collider workshop in Warsaw (June 9-12, 2008), the present status of the calorimetry performance simulations and hardware R&D for the three ILC detector concepts will be summarised. The ILC calorimetry studies will then be addressed in the light of their validity for a CLIC experiment. As a result, a first draft calorimetry working plan for the CLIC detector study team will be presented for discussion.  

The general goals of the series of the ILCDR Workshops are to identify R&D specific topics for the damping rings, review their present status and understanding through technical presentations and discussions, and lay out an R&D plan. The ILCDR08 at the Cornell University has focused on the subjects of Electron Cloud and Low Emitttance Tuning, by bringing together world experts to provide guidance and suggestions for the CESR-TA program, which will be carried out over 2 years of flexible experimental operations.
The scope of this presentation will be to give a general overview on the results presented in the ILCDR08 Electron Cloud sessions, and the relative discussions. The four dedicated EC Working Sessions included the review of recent experimental results, simulation codes, mitigation techniques and future experimental planning. The main charge of the EC Working Group was to ultimately identify a set of e-cloud experimental tests that could be scheduled as part of the CesrTA program. These tests should be finalized to the validation of electron cloud modelling tools (both build-up and instability simulations), where possible in a parameter range relevant for the ILC (CLIC) damping rings, and to the demonstration of the techniques for mitigation of electron cloud effects, which would allow operation of the damping rings.

The Advanced Beam Dynamics Workshop NANOBEAM-2008, organized by the Budker Institute of Nuclear Physics, took place during the last week of May in the Russian city Novosibirsk, the so-called capital of Siberia. Two previous Nanobeam workshops took place at Lausanne (Switzerland) in 2002 and at Uji (Japan) in 2005. The topics covered by the workshop this year include Linear Colliders as well as Advanced Beam Science and Technology. The highlights from Nanobeam’08 are presented.

An overview of the status of the commissioning of two spectrometers, based on segmented dumps, used for time resolved energy measurements of the beam.

Within the framework of the second Joint Research Activity PHIN of the European CARE program, a new photo injector for the CTF3 drive beam has been designed and is now being constructed in collaboration between LAL, CCLRC and CERN. The laser driven rf photo injectors are recent candidates for high-brightness, low-emittance electron sources motivating the research on emittance compensation theory and precise emittance measurement techniques.
Beam dynamics simulation results, obtained from PARMELA code, are presented. After summarizing the emittance growth mechanism for the photo injectors, the emittance measurement by the pepper-pot method, that will be implemented on the beamline, is discussed. Finally the pepper-pot measurement results from the PSI OBLA 500 kV test-stand are presented.

A study to improve CTF3 automatic steering is in progress, involving tests of dispersion-free steering as well as improved model identification routines (needed for model-based steering).  The  test-case for this study will be the CTF3 linac.  The presentation gives the status and outlooks of this work.

Installed just beyond the Delay Loop in CTF3 is an RF pick-up which measures the electromagnetic field frequency spectrum of the passing particles. The RF signals are split to be measured into four separate frequency bands and we can record the amplitude and phase of these signals and from there calculate the length of the particle bunches. It is important to monitor these lengths to ensure that ideal beam parameters are held through different structures in CTF3. I will present the work that has been done in both the online and offline analysis code to examine the signals and present results of a recent scan.

The CLIC pre-damping rings have to accommodate a large emittance beam, coming in particu lar from the positron target andreduce its size to low enough values for injection into the main damping rings. Linear lattice design options based on an analytical approach for minimum emittance cells are presented. In particular the parameterisation of the cells quadrupole strengths and optics function with respect to the emittance and drift lengths is derived. Complementary considerations regarding constraints imposed by polarized positron stacking are also considered.

Triggered by the RF frequency reduction of the CLIC main linac cavities, the damping ring parameters had to be re-evaluated and the ring's performance adapted to the new luminosity requirements. In particular, the ring's lattice is being re-designed in order for the magnet parameters to become less challenging. The progress in other areas such as wiggler design, radiation absorption non-linear dynamics and collective effects will be presented.  In view of a staged approach for reaching the ultimate CLIC energy, conservative output emittances are scaled from operating or approved synchrotron lattice source projects. To this end, the dependence output emittances is evaluated with respect to different beam parameters such as bunch population, beam energy and longitudinal beam characteristics.

The fatigue of the accelerating structures material due to cyclic heating arising from induced eddy currents is still considered as a critical issue. Until now it is unclear to which extent the fatigue impairs the performance of the structure through the lifetime. Recent experiments showed that surface roughness and even small surface cracks did not influence the Q-factor which is linked to the RF-performance. In terms of breakdown there are several theories how fatigue phenomena increase the breakdown rate.
An overview of four experiments to assess fatigue behavior is presented. Namely: conventional fatigue test, pulsed laser test, ultra sound swinger test and RF-fatigue test. The experimental results obtained so far will be discussed and interpreted with the help of material characterization techniques available at CERN and the Ruhr-University Bochum.

This talk will focus on the characterization of the beams of electrons and protons with energies above a few MeV produced in the interaction of an ultra-intense (~10^19 W.cm-2) laser beam with a 10 µm thick solid target.
The properties of these beams (transience, intensity and continuous energy distribution especially) make their characterization complex and leaded us to develop specific methods. I will present these ones along with experimental results obtained in different facilities for the study of the electron beams as a function of the target material.
I will also briefly discuss an experiment carried out with similar techniques to characterize the proton beam produced at an higher power laser facility. This experiment demonstrated the possibility to induce nuclear reaction in a plasma and to measure quantitatively the reaction rate in preparation. This opens the way to probing  of the perturbation of the nucleus-electronic shells coupling by a strong electromagnetic field.

The petawatt laser power was achieved as early as in 1997 based on chirped pulse amplification in Nd:glass. Many institutes are going to obtain this power level, but any substantial increase is limited in principle by the reasons mentioned below. All devices and projects now available may be classified into three types according to the gain medium they employ: 1) neodymium glass, 2) Ti:sapphire and 3) optical parametric amplifiers with KDP and DKDP crystals.
A narrow bandwidth of Nd glasses restricts typically the compressed pulse duration to about 500 fs. Small (10cm) aperture of Ti:sapphire crystals limits the pulse energy due to optical breakdown and self-focusing. Parametric amplifiers are free of above disadvantages. DKDP crystals have an aperture of 40 cm and more and the gain bandwidth corresponds to the 15 fs duration of the amplified pulse. Thus, using an optical parametric amplifier is one of the most promising ways of overcoming the petawatt power barrier.
We will discuss the petawatt laser facility in the Institute of Applied Physics of Russian Academy of Science (Nizhny Novgorod) and also the most promising applications of such lasers: electron and ion acceleration.

The CLIC Final Focus System has a chromaticity four times larger than the ILC and its scaled testbed ATF2. In order to prove the feasibility of CLIC-like systems we have proposed to reduce the ATF2 IP betas by a factor of four. This will also  serve to study the tuning difficulty versus IP spot size hoping to extrapolate to the smaller beam sizes of ILC and CLIC. Andrei Seryi's recent proposal of doubling the CLIC L* will  also be briefly discussed.

There is a strong request for high intensity polarised positron beams for e-/e+ linear colliders (ILC, CLIC). In order to fulfill this request, two schemes of polarised positron source have been studied: Undulator based and Compton based. I will present a brief introduction to Compton based polarised positron sources and will focus in particular on the capture section scheme, showing the design and simulation results of a capture section studied at LAL-Orsay for the ILC, and considering the changes necessary to fit the CLIC requirements.

Since 1995 research and development of permanent magnets has been done at Fermilab. The most important effort was the building of the Recycler ring for storage of anti protons. This is a 3.6 km in circumference ring made with 486 magnets all using strontium ferrite permanent magnets. Up to 450 x 10^10 anti protons are stored in this ring. Basic design parameters and assembly techniques used for the recycler will be discussed. In addition work done on adjustable quadrupole magnets will be discussed. These are high field (greater than 100 Tesla per meter gradient) quadrupoles with an adjustable gradient of 20% of full field.

Understanding slow and fast ground motion is important for the successful operation and design for present and future colliders. Since 2000 there have been several studies of ground motion at Fermilab. Several different types of hydro static water levels have been used to study slow ground motion (less than 1 Hertz) seismometers have been used for fast (greater than 1 Hertz) motions. Data have been taken at the surface and at locations 100 meters below the surface. Data and results of both slow and fast ground motion will be discussed in particular the effects of natural and cultural sources of motion.