Ion Source Requirements in High-Intensity Linacs (Production of high intensity ion beams)

• Mohammad Eshraqi (ESS - European Spallation Source (SE))

High-intensity linear accelerators have a wide range of applications, including driver for accelerator-driven sub-critical reactors, transmutation of nuclear waste, injectors for colliders, and spallation neutron sources. High-intensity linacs are designed to minimize the losses to increase component longevity and allow hands-on maintenance. Depending on the application, emittance growth and control of the final emittance are major parameters to have under control during the design of the accelerator. Even though the losses are present along the entire linac, and the design of the linac governs how the emittance evolves, the ion source is undoubtedly the single component with the highest impact on defining the beam behavior along the linac. In this paper, by using the European Spallation Source as an example, we discuss how the requirements of the linac dictate the parameters of the ion source, from the extraction energy to the jitter on the extracted current.

New Commissioning Results of the MIST-1 Multicusp Ion Source (Production of high intensity ion beams)

• Daniel Winklehner (Massachusetts Institute of Technology)

For the sterile neutrino experiment IsoDAR (Isotope Decay-At-Rest), we have developed a compact particle accelerator system delivering a 10 mA, continuous wave (cw) proton beam at 60 MeV to a neutrino production target. The accelerator comprises a compact isochronous cyclotron, an RFQ embedded in the cyclotron yoke, and an ion source. To reduce space charge effects during injection and acceleration, we are accelerating H₂⁺ instead of protons. To produce the needed cw H₂⁺ beam current of 10 mA (nominal) at the required purity and quality, we have built a new filament driven, multicusp ion source (MIST-1). Here we report commissioning results for long-time running at reduced power, demonstrating the feasibility of the design. Highlights include an H₂⁺ beam current density of 12 mA/cm², > 80 % H₂⁺ fraction, and emittances of 0.05 π-mm-mrad (RMS, normalized) after extraction. We also present high fidelity simulations that are in good qualitative and quantitative agreement with emittance measurements in our test beam line.

High Intensity High Reliability Laser Ion Source Development at IMP (Production of high intensity ion beams)

• Huanyu Zhao (Institute of Modern Physics, Chinese Academy of Sciences)

The capability of the high intensity high charge state ion pulse production from light to medium-mass elements had been demonstrated by the laser ion source developed at IMP. Especially in terms of C6+ yield, the laser ion source can meet the requirements of cancer therapy facilities for filling the synchrotrons in a single turn injection mode. But for practical applications, the capability of long-term, continuous operation, repeatability and stability of the ion source is also what one must concern with. With the help of a new-developed control system and customized targets, the continuous operation of the laser ion source with the repetition rate below 1 Hz for tens of hours has been realized. The shot-to-shot fluctuations of the main ion pulse parameters, total charge quantity, pulse duration (FWHM) and peak current, were 5%, 8% and 11.5%, respectively, which are comparable with those obtained in single-shot operation mode and acceptable for the applications of laser ion sources.

High Power Operation of Superconducting ECR ion Sources (Production of highly charged ion beams)

• Liangting Sun (Institute of Modern Physics, CAS)

Third generation ECR (Electron Cyclotron Resonance) ion sources developed with high field, high frequency and high power technologies are aiming to produce intense highly charged ion beams for accelerators. Operating at 24~28 GHz, those ion sources have the potentials to be heated with microwave power of ~10 kW which is essential for the production of very high charge state ion beams. Scientific researches and accelerator operation at IMP inquire the superconducting ECR ion sources capable of running at the conditions close to their peak performances. Recently, ~300 eμA Kr26+, ~200 eμA Xe32+ and ~6 eμA Ar18+ beams have been continuously delivered by the ion sources SECRAL-II and SECRAL-I. This paper will present the status of the ion sources routinely operated at high power up to 8 kW. Challenges and critical issues for long-term high power operation will be discussed.

Development and Status of the FRIB 28 GHz SC ECRIS (Production of highly charged ion beams)

• Haitao Ren (FRIB)

To meet a beam power requirement of 400 kW for heavy ions, a high intensity 28 GHz superconducting ECR ion source is under development at the Facility for Rare Isotope Beams (FRIB) in collaboration with Lawrence Berkeley National Laboratory (LBNL). The magnet was built and tested at LBNL and integrated into the ion source cryostat on the FRIB high voltage platform. Magnet cooldown to 4.2K was completed successfully in December of 2020. The static heat load at 4.2K has been measured to be around 1.2 W, in good agreement with the design value. The heat load is managed through 2 GM-JT cryocoolers that have been in operation for several months. Magnet energization and field mapping are schedule in July of 2021. Warm components preparation and assembly test are ongoing in parallel. 18 GHz Klystron amplifier has been tested with a dummy load. The ion source commissioning with 18 GHz Klystron shall start in October of 2021. Details of the ion source development, status, and commissioning plan will be presented in the paper.

High B-min Quasi-Stable Operation Regime of an Electron Cyclotron Resonance Ion Source (Production of highly charged ion beams)

• Ivan Izotov (IAP RAS)

Fundamental studies of excitation and non-linear evolution of kinetic instabilities of strongly non-equlibrium hot plasmas confined in open magnetic traps suggest new opportunities for fine-tuning of conventional electron cyclotron resonance ion sources (ECRIS) widely used for generation of high charge state ions. We report on experiments with a 14 GHz ECRIS , in which adopting the new approach allows to shift the charge state distribution and increase the current of extracted high charge state ions up to two times, achieving, in particular, 95 $\mu$A of O$^{7+}$ with a modest heating power of 280 W/11.56 GHz. A theoretical model supporting and explaining the experimental findings is proposed. The implications on the commonly used semi-empirical scaling laws for ECRISes are discussed.

The AISHa Source for the CNAO Facility (Production of highly charged ion beams)

• Luigi Celona

AISHa is an ECR ion source operating at INFN-LNS designed taking into account the typical requirements of hospital facilities, where the key issues are the source reliability optimization and fast maintenance operations together with low ripple, high stability and high reproducibility of the beams produced. In the framework of the IRPT and INSpIRIT projects and in collaboration with CNAO, further upgrades are underway to produce high intensity beams of Oxygen, Helium and Lithium, new candidates for their better lateral dose distribution compared to protons and lower biological efficacy compared to Carbon ions. In particular the AISHa source will be equipped with a dedicated oven which will expand the potential of CNAO in the research field, with a longer-term goal of introducing into clinical practice new ionic species more effective for tumours treatment, and in industrial sector due to the capability of producing metal beams of interest in the aerospace field.

Duoplasmatron Type Molecular Carbon Ion Source (Applications and related technologies)

• Motoi Wada (Doshisha University)

A duoplasmatron ion source with the carbon plasma electrode has successfully produced poly-atomic carbon ions up to C$_6^+$. The intermediate electrode has six holes to guide cathode plasma to the carbon discharge anode performing as the plasma electrode. A 1 mm diameter extraction hole is opened at the center of the carbon plasma electrode, where is no exposure to the plasma from the cathode region. The ion source maintains a stable discharge with both H$_2$ and Ar as discharge support gas, but works better at lower pressure with Ar. A hydrogen plasma produced molecular ions of hydrocarbons while Ar plasma delivered a beam with the mass peak corresponding to Ar$_2^+$ with the intensity about one-eighth of Ar$^+$ peak. With 150 W discharge power, the source produced about 1 micro-ampere of mass separated C$_6^+$ ion current.

First Injector Commissioning Results with Helium Beam at MedAustron Ion Therapy Center (Applications and related technologies)

• Nadia Gambino (MedAustron)

MedAustron is a synchrotron-based Particle Therapy Accelerator located in lower Austria which delivers clinical proton and carbon beams in the range of 62-252.7 MeV/u and 120-400 MeV/u respectively in two treatment rooms. A proton Gantry was recently commissioned in a third clinical treatment room and a fourth experimental beamline is dedicated to non-clinical research activities. Within the latter, the injector commissioning has recently started for He2+ beam generation. The long-term goal is to use helium for cancer treatment due to its favourable physical and biological properties. The MedAustron injector features three identical Electron Cyclotron Resonance Ion Sources (ECRIS) from Pantechnik, providing each a 8 keV/u beam. Two sources are respectively used for proton and carbon beams production. The third source is the test bench for helium beam generation. In this work the first He2+ beam commissioning results at the injector level are presented. The helium beam properties from the source up to injection further downstream into the accelerator, i.e. from the Low Energy Beamline to the Linear Accelerator are discussed in terms of beam emittance, intensity and transmission efficiency. A comparison with simulated data is also presented.

Laser-Driven Ion Acceleration and Multidisciplinary Applications at ELI (Production of high intensity ion beams)

• Daniele Margarone (Institute of Physics o the Czech Academy of Sciences)

Recently the ELIMAIA (ELI Multidisciplinary Applications of laser-Ion Acceleration) beamline has been installed at ELI-Beamlines in the Czech Republic. The main goal of ELIMAIA is to offer short ion bunches accelerated by lasers with high repetition rate to users from different fields (physics, biology, material science, medicine, chemistry, archaeology) and, at the same time, to demonstrate that this source can be delivered through innovative and compact approaches. In fact, ELIMAIA will provide stable, fully characterized and tuneable particle beams accelerated by PW-class lasers and will offer them to a broad community of users for multidisciplinary applied research, as well as fundamental science investigations. ELIMAIA will also enable to use laser-driven proton/ion beams for medical research thanks to the reliability and accuracy of its particle beam transport and dose monitoring devices. The current status of commissioning of the ELIMAIA beamline, along with experimental results on innovative targetry and diagnostics for laser-driven particle acceleration is presented and discussed, including preliminary tests carried out during the ramp up phase of the HAPLS (L3), PW-class, 10 Hz laser system at ELI-beamlines.

Design and Operation of a Penning Ion Trap Source for the CHIP-TRAP Mass Spectrometer (Applications and related technologies)

• Madhawa Horana Gamage (Central Michigan University)

The CMU High Precision Trap (CHIP-TRAP) mass spectrometer at Central Michigan University will be used to perform precise mass measurements on stable and long-lived radioactive isotopes. As part of this project, we have developed a Penning Ion Trap (PIT) source capable of producing singly-charged, low intensity, ion bunches (~ 100s to 1000s of ions) from gaseous species with pulse widths of ~1 µs. The PIT Source is similar to a PIG type ion source, but consists of a miniature cylindrical Penning trap, comprised of two end caps and a center ring with a trap volume of about 0.8 cm$^3$, housed inside a permanent neodymium ring magnet. Gas enters the trap through a hole in the end cap with the flow controlled by a precision leak valve. Gas is ionized by an ~1 µA electron beam from a thermal tungsten emitter applied for ~1 µs. After a short confinement period, ions are released from the trap by dropping the voltage on one of the end caps and extracted into the beamline. In this presentation, I will describe the design, operation and recent calibration results of the PIT source.

Radioactive and Stable Ion Beam Production at GANIL-SPIRAL 1&2 (Radioactive ion beams, charge breeders and polarized beams)

• Mickael DUBOIS (CNRS)

GANIL Facility delivers ion beams from Proton to Uranium up to 95MeV/A. The cyclotron facility provide stable (since 1983) and Radioactive Ion Beams (RIB) (since 2001) for Physics experiments. R&D of new stable and RIB beams are steadily under progress matching physicist requirements. The SPIRAL1 facility was upgraded to extend its capabilities to RIB of condensable elements. After a new RIB produced in 2019, off-line R&D’s were done on the Target Ions Source System and Charge Breeder to improve efficiencies and achieve an operational and reliable facility. The commissioning of the LINAC-SPIRAL2 accelerator started in 2019 with a Proton beam. In 2020, a 16 kW proton beam was obtained and delivered for the first time on the NFS physic area, and a 4 mA beam of 4He2+ was produced with the PhoenixV3 ECR ion source. An overview of Ion sources, beam properties and future developments will be described for a long-term operation mode.

Measurement of Ionization, Charge Exchange and ion Confinement Times in Charge Breeder ECR Ion Sources with Short Pulse 1+ Injection of Metal Ions (Fundamental processes)

• Miha Luntinen (University of Jyväskylä, Department of Physics)

The Consecutive Transients (CT) method has been developed to calculate the characteristic times of ionization, charge exchange and ion confinement within highly charged plasma of a Charge Breeder Electron Cyclotron Resonance Ion Source (CB-ECRIS). In the CT-method, 1+ ions are injected into the plasma in pulsed mode and fits are made to the resultant high charge state extraction current transients. An optimization procedure is then used to determine the plasma parameters from the fitting coefficients. Results obtained with the CT-method are compared in two different CB-ECRIS operating configurations. It is shown that the differences in CB efficiencies between the two configurations (e.g. 8.9% and 20.4% for K9+) are explicable through the change in the characteristic times, which are themselves compatible with the nested-layer model of the spatial distribution of ions and electrostatic ion confinement.

Improvement of Velocity Distribution Function of Hydrogen Atoms in Ion Source Discharges (Fundamental processes)

• Tatsuhiro Tokai (Doshisha University)

A negative hydrogen ion source is operated by injecting Cs to reduce the amount of coextracted electron current while maintaining large extraction current of negative hydrogen (H-) ions. The production efficiency of H- ions from the low work function Cs covered plasma grid (PG) surface should be heavily dependent upon the velocity distribution of hydrogen atoms (H0) striking the PG surface and an electron cyclotron resonance plasma source is studied the performance if it can efficiently produce high speed H0 without contaminating the cesiated PG surface. A system to measure the H0 velocity distribution functions has been designed and the performance is being improved. A pumping capacity of the H0 ionizer section of the system is increased so as to make the velocity distribution function measurement with enough signal to noise ratio.

Energy Distribution and Bremsstrahlung Spectra of Energetic Electrons Ecaping from the ECR Plasma with High Energy Input (Fundamental processes)

• Elena Kiseleva (Institute of Applied Physics of the Russian Academy of Sciences (IAP RAS))

Electron energy distribution function (EEDF) is an important parameter that defines the processes of plasma confinement and ionization. Understanding such processes is crucial for the tuning of ion sources. In the ECR plasma, the EEDF takes a significantly non-Maxwellian shape that still remains unknown. As the continuation of this problem solving, the energy distributions of the electrons lost from the magnetic mirror trap were directly measured in a wide range of neutral gas pressures and gyrotron powers along with bremsstrahlung spectra. A series of experiments was performed on the newly constructed Gasdynamic Ion Source for Multipurpose Operation (GISMO) facility allowing record-breaking specific energy input into the plasma. Obtained distributions showed unconventional behavior as the function of external parameters. The EEDF shape and the bremsstrahlung spectra showed a significant qualitative change with the gyrotron power as a result of the development of kinetic instabilities

Cutoff Limitation of Left-Hand Polarization Wave and Candidates for Further Enhanced Producing Multicharged Ions on ECRIS (Fundamental processes)

• Yushi Kato (Osaka Univ.)

Based on experimentally obtained plasma parameters in ECRIS and theoretical considerations, it turned out the essential factor that is currently presumed to define the increase in multicharged ion current in ECRIS is not simply the density limit of ordinary wave and right-hand cut-off, but is also higher density one of left-hand cutoff in magnetic field. There are two response guidelines that can be considered to make it possible to overcome limitations, except for the conventional simply increasing the frequency and the magnetic field strength. One is advanced high-frequency resonance, which is conversion from electromagnetic to electrostatic wave essentially without cut-off. The other is due to the introduction of lower frequency waves than ECR’s one, which has no density limit in a more essential sense. The latter is the introduction of lower hybrid resonance and ion cyclotron resonance. We will describe experimentally obtained plasma parameters, and will discuss these applications.

CANREB EBIS Commissioning at TRIUMF (Radioactive ion beams, charge breeders and polarized beams)

• Brad Schultz (TRIUMF)

The Canadian Rare isotope facility with Electron Beam ion source (CANREB) is an essential part of the Advanced Rare IsotopE Laboratory (ARIEL) presently under construction. CANREB was recently commissioned at TRIUMF and can accept stable or rare isotope beams from a variety of ion sources, delivering high purity beams of highly charged ions (HCI) to experiments. The injected beams are bunched using an RFQ cooler/buncher, and energy adjusted using a pulsed drift tube for injection into the Electron Beam Ion Source (EBIS) charge state breeder. The EBIS is designed for a maximum electron beam current of 500 mA and a maximum magnetic field strength of 6 Tesla. Ions with energies up to 14 keV can be injected and HCI with 3 < m/q < 7 can be charge bred and extracted. The HCI are m/q-selected using a Nier-type spectrometer, before being transported to the linac for post-acceleration. Results from CANREB beam commissioning with focus on the EBIS will be presented.

Optimization of Ion Transport in a Combined RFQ Cooler with Axial Magnetic Field (Radioactive ion beams, charge breeders and polarized beams)

• Marco Cavenago (INFN-LNL)

The accurate mass spectrometry (with resolution goal 1:20000) of exotic ions requests beams with low energy spread (goal is about 0.5 eVrms or lower) and low tranverse emittance; so it is necessary to cool ions produced by a spallation source of a factor from 5 to 10. In a radiofrequency (rf) quadrupole cooler (RFQC), collisions decrease ion kinetic energy, while rf and bias voltages confine and reaccelerate ions towards the extraction, where the cold ion beam is formed. Operation is based on carefully chosen voltage tunings, and among others: the dependence on ion species and gas pressure, which requests an adequate pumping system; the difficult design of an efficient ion extraction, which critically depends on residual ion speed. Progresses in the experimental setup are described. Indications from simple ion tracing, ion+collision tracing and some limited Monte Carlo simulations are compared. Results are applied to the comparison of triode and tetrode design of the extraction system.

Charge Breeder at GANIL: Metal Charge Bred Elements (Radioactive ion beams, charge breeders and polarized beams)

• Laurent MAUNOURY (CNRS)

The charge breeder of the SPIRAL1 (SP1CB) facility provided this year to physicists with new Radioactive Ion Beams (RIB) showing significantly improved performances. They were obtained thanks to studies conducted off-line with 1+ ion produced by FEBIAD and ECR ion sources. The SP1CB established its capability to boost efficiently condensable elements such as $^{19}\textsf{Fn}$+, $^{24}\textsf{Mgn}$+, $^{32}\textsf{Sn}$+ and $^{54}\textsf{Fen}$+. The charge breeding efficiencies have been investigated regarding several parameters. The deltaV curves of stable elements as well as radioactive ones were recorded for high charge states, trends will be discussed in more detail. Finally, as molecular beams provide some advantages compared to atomic ion beams for selecting isobaric species, one may wonder if the charge breeding efficiencies is still effective. The performances of the 1+/N+ process were investigated using SF6 molecules broken down into SFx1+ ions and compared to regular F1+ and S1+ ions. This contribution will deal with these topics.

Studies of Bemsstrahlung and Characteristic X-Ray Lines Using the VENUS ECR (Beam extraction, transport, and diagnostics)

• Janilee Benitez (Lawrence Berkeley National Laboratory)

Though known for their production of high currents of highly-charged ion beams, advanced electron cyclotron resonance (ECR) ion sources like VENUS at Lawrence Berkeley National Laboratory (LBNL) also generate significant numbers of x-rays. The LBNL ECR ion source group has spent many years studying the x-rays emitted from VENUS in order to gain a better understanding of the ECR plasma. Based on the emitted bremsstrahlung continuum, a spectral temperature Ts can be calculated which is a relative indication of the temperature of the plasma electrons. We will present correlations between Ts with respect to parameters such as magnetic fields. In addition to the bremsstrahlung continuum, the plasma ions emit characteristic x-rays. We will show that additional information can be gained by investigating spectral line shifts. A summary of this recent research using VENUS will be presented and discussed.

A New Extraction System Design with a Strongly Inhomogeneous Electric Field for a JYFL Electron Cyclotron Resonance Ion Source (Beam extraction, transport, and diagnostics)

• Sergey Vybin (IAP RAS)

A new ECR ion source extraction system has been designed. The design is based on the extraction conditions of the JYFL 14 GHz ECRIS, and its performance is compared to the existing extractor. The new design aims to improve the beam formation and beam quality of high intensity ion beams. The plasma and the puller electrodes shape was changed. The plasma electrode has a narrow tip extruding towards the puller. It causes the redistribution of the electric field in the extraction region. The extractor was developed with IBSimu. The initial beam parameters were taken from the experimental data. The calculations showed that the new extraction system allows to increase the total current without compromising the beam quality. The new design allows the beam formation optimization for lower extraction voltages overcoming the present space charge limit.

Tubular Electron String Ion Source Development (Production of highly charged ion beams)

• Alexey Boytsov (Joint Institute For Nuclear Research, Russia, Dubna)

Tubular Electron String Ion Source(TESIS) is being developed to significantly increase ion output. Tubular electron beam is generated in electron string mode. Such configuration should make it possible to increase the electron trap capacity and, accordingly, the ion output. Numerical results of modeling the motion of the beam for the design of electron optics are carried out. The experimental setup consists of the cryocooler based cryostat and the superconducting solenoid. The electron gun with the annular composite cathode, the electron reflector and drift tubes with the central rod have been designed and installed. The electron gun control system has been tested. The results on the accumulation of electrons in the electron string mode have been obtained. Ion motion control is discussed.

Operation Experience of LION and RHIC-EBIS for RHIC and NSRL (Production of highly charged ion beams)

• Takeshi Kanesue

LION is a laser ion source to provide singly charged heavy ions of various species for RHIC-EBIS. Ion beams are used for RHIC physics experiments and for NASA Space Radiation Laboratory (NSRL) quasi-simultaneously. The demands for beams are growing and more and more ion species are used due to unique capability of the sources. Ion species can be switched on a pulse-by-pulse basis not affected by previously used species. LION can produce ion beams from any solid material. We will present the performance and experience of LION and RHIC-EBIS.

A Picosecond Laser-Based Ion Source for Injection into a High Capacity EBIS in Both Accumulation and Single Pulsed Modes (Production of highly charged ion beams)

• Sergey Kondrashev (BNL)

Ps-lasers have advantages for generation of low charge state ions compared to ns-lasers because the influence of heat conductivity on a solid target is negligible in the case of ps-laser ablation for laser pulse durations shorter than 10 ps. By using a laser with high rep-rate, it is possible to produce quasi continuous 1+ ion beams for periods up to tens of milliseconds, making it possible to take advantage of the ability of the EBIS to trap 1+ ions in accumulation injection mode. We studied the properties of Al, Ti, Cu, Nb, and Ta plasmas generated by a ps-laser with 1.27 mJ energy within an 8 ps pulse to investigate feasibility and specify parameters of a laser ion source for RHIC EBIS using accumulation injection mode. It is shown that a both accumulation and single pulsed injection modes are accessible with a single ion source geometry and single injection line, providing the most attractive option for an ion source for external injection into RHIC EBIS trap based on a ps-laser.

Overview of Recent and Upcoming Activities at the BATMAN Upgrade Test Facility (Ion sources for fusion)

• Christian Wimmer (Max-Planck-Inst. f. Plasmaphysik)

The BATMAN Upgrade (BUG) test facility at IPP is contributing to the development of RF-driven H$^–$ sources towards the ITER neutral beam injection and beyond. BUG is equipped with an 1/8 size of the ITER NBI ion source and thus is highly flexible for setup changes or diagnostic access. The present strategy for BUG is aligned along two paths: (i) BUG is continued upgrading for long pulse operation (up to 1 hour, both in H and D) to identify measures for the stabilization of long pulses. For that, a Cs evaporation concept with evaporation close to the extraction system is being tested, showing a stabilization of co-extracted electrons in 100 s H pulses. (ii) BUG is used for investigations of whole beam and beamlet optics for which the beam diagnostics have been massively upgraded. A newly installed MITICA-like extraction system including asymmetric deflection compensation magnets shows a good compensation of the row-wise horizontal zig-zag deflection of the beam.

First Operations with Caesium of the Negative Ion Source SPIDER (Ion sources for fusion)

• emanuele sartori (unipd)

The negative-ion beam source SPIDER, which is the full-scale prototype source for the ITER neutral beam injector, recently started the operation with caesium. This experimental phase follows three years of volume operation, devoted to the commissioning of the plants and to the integrated test of the ion source and accelerator. The ion source, composed of eight RF drivers connected to a large plasma chamber from which the negative ions are extracted, was operated up to a RF power of 400kW, and beam energy up to 50kV, and plasma discharges limited to less than one minute This contribution will describe the main results of the first campaign with caesium in SPIDER. The repetition of short plasma and beam extraction blips with different injection rates was applied, to study the effect on plasma and beam parameters. The caesiation procedure adopted in SPIDER will be described (caesium injection rate, duty cycle of plasma-on, RF power, source gas pressure) together with the effects of the source parameters on the extracted beam and its uniformity. Even though the use of a much reduced number of beamlets was a strong limitation in terms of total accelerated current (a mask at the plasma grid covered 1252 apertures over 1280 to limit the gas load to the vacuum pumps), it provided advantages in the study of the caesium effect on the beam, such as the introduction of dedicated diagnostics for the single beamlets, and the identification of the beamlet current and optics.

Ion Source Development at IPP: on the Road Towards Achieving the ITER‐NBI Targets and Preparing Concepts for DEMO (Ion sources for fusion)

• Ursel Fantz (Max-Planck-Institut for Plasma Physics)

ITER’s neutral beam injection (NBI) systems are based on generation of negative hydrogen ions in a caesiated RF-driven ion source, their electrostatic acceleration and neutralisation in a hydrogen gas target. The large ion source (0.9 m×1.9 m) with 1280 apertures has to deliver 57 A D− for 3600 s (286 A/m2) and 66 A H− for 1000 s (329 A/m2). The RF ion source test facilities ELISE and BUG at IPP are aimed to demonstrate the ion source parameters, the homogeneity of the large beam (roughly 1 m×1 m) and its divergence. While the ITER parameters could be demonstrated in hydrogen, the achievement in deuterium for long pulses is still pending due to the large fraction of co-extracted electrons, their temporal dynamics and inhomogeneity in vertical direction, limiting the ion source performance. The contribution summarizes the achievements and challenges experienced in view of ITER and reports on the IPP contributions to an EU DEMO (DEMOnstration reactor) based on a similar source concept.

Inductive Coupling Between RF and Plasma: Insights and Consequences for H$^–$ Ion Sources (Ion sources for fusion)

• Stefan Briefi (Max-Planck-Institut für Plasmaphysik)

The plasma in RF driven negative hydrogen ion sources is sustained via inductive coupling with large power levels of up to 100 kW and low frequencies around 1 MHz. This leads to currents of around 100 A flowing over the RF coil and corresponding voltages in the kV range. The associated risk of arcing limits the reliability of the whole ion source. The required power level can be reduced via optimizing the RF power transfer efficiency, which is typically only in the range of 50 to 60%. For enabling a fundamental insight into the RF coupling mechanisms at the operational parameters of the ion sources, a self-consistent fluid model has been set up (details of the model are presented in the contribution to this conference by D. Zielke et al.). The model was successfully validated with experimental measurements at the BATMAN Upgrade test bed. Optimization studies revealed that the RF power transfer efficiency can be improved to 90% by increasing the driver length and the RF frequency.

Development of a Cs-Free Negative Hydrogen Ion Source System Using Multi-Pulsed Plasma Sources: Prospect and Challenges (Negative ion sources)

• Sung-Ryul Huh (Korea Atomic Energy Research Institute)

KAERI has recently developed a novel hydrogen ion source system for fusion and particle accelerator applications. The main feature of this system is the use of source pulsing based on the volume production mechanism to improve the efficiency. The pulsing is a method of modulating plasma power and so the electron energy, providing a favorable condition (the after-glow) for negative ion generation. Its only drawback is, however, that it is unable to continuously supply the negative ions to an extraction system because inherently transient. To remedy the drawback, we have introduced a multi-pulsing method. The system operates with alternating pulsing sequences corresponding to two plasma sources, thereby generates the after-glow states in an alternating manner. This enables the system to continuously supply the negative ions in terms of the whole. In this presentation, the concept, proof-of-concept results, and also prospect and challenges of the system will be presented and discussed.

Effect of Negative Ion Sheath on Beam Extraction in Negative Hydrogen Ion Sources (Negative ion sources)

• Katsuya Hayashi

The shape of a negative ion emitting surface (plasma meniscus) near the extraction aperture is important for the beam quality of the H$^-$ ion beams from H- ion sources. A lot of H$^-$ surface-production cause the ion-ion sheath, which can affect meniscus shape. In this study, effects of H$^-$ surface-production and the ion-ion sheath structure on the meniscus are numerically investigated by 3D PIC model KEIO-BFX code [1]. KEIO-BFX simulation has shown that with increasing in the surface-produced H-, the ion-ion sheath forms near the extraction aperture and it prevents the penetration of the extraction electric field. In the presentation, more detailed analysis, such as the dependence of the ratio nH$^-$/ne will be discussed. [1] S. Nishioka, et al., J. Appl. Phys. 119 (2016) 023302.

H-Ion Source Operational Performance and Latest Development at the Spallation Neutron Source (Negative ion sources)

• Baoxi Han (Oak Ridge National Laboratory)

The Spallation Neutron Source (SNS) at Oak Ridge National Laboratory is the world most powerful accelerator driven pulsed neutron source. A H- injector feeds the accelerator with the required high current (>50 mA) time structured (1ms, 60 Hz) H- beam. The injector consists of an RF-driven, Cs-enhanced H- ion source and an electrostatic low energy beam transport section. In the recent three run cycles, the H- source operated ~4 months for each run without intrusive maintenance. Post-service inspections revealed no significant wear or damage that would have limited further operation of the source. A single dose of cesiation conducted in the startup of a run maintained the beam current for the entire run period with just minor adjustments of operation parameters. Lately, we have tested a solid-state RF power system to replace the vacuum-tube type RF supply to further improve the ease of operation and system availability. Significant progress has also been made on the continued development of the external-antenna RF ion source including its plasma ignition scheme and stability.

Optimization of a Negative Ion Source for Accelerator Mass Spectrometry using Lorentz 2E (Negative ion sources)

• Collin Tiessen (Andre E. Lalonde Accelerator Mass Spectrometry Lab)

Accelerator mass spectrometry (AMS) is a highly sensitive technique used for the analysis of long-lived radioisotopes. Such measurements are useful in geology, archeology, environmental tracer studies, nuclear waste monitoring, and nuclear forensics. The cesium-sputter negative-ion source acts as a sample injector and, in the cases of carbon-14, aluminum-26, and iodine-129, an isobar suppressor. Integrated Engineering Software’s Lorentz 2E ion optics software has been used to model the electrodynamics within the ion sources at the A. E. Lalonde AMS laboratory. These simulations include and demonstrate the importance of space-charge effects from the positive cesium ion sputtering beam on the negative ion sample beam. This presentation will illustrate the use of Lorenz 2E to optimize the emittance of the outgoing negative ion beam, while simultaneously maintaining the focusing of the cesium ions on the sample material. These results will be compared with experimental observations.

Dynamics and Reactivity of Thermalized Ions in a Radiofrequency Quadrupole Gas-Reaction Cell Used for the Production of Radioactive Molecular Ions (Radioactive ion beams, charge breeders and polarized beams)

• Jean-Francois Alary (Isobarex Corp.)

Two-dimensional Radiofrequency Quadrupole (RFQ) ion guides are versatile tools that are used over a wide range of ion energies. Properly tuned, they can provide an ideal environment for ion-molecule chemistry to proceed by allowing thermalized ions to react on-line with gaseous reactants. We exploit this capability in the Ion Reaction Cell (IRC), an RFQ-based system designed to form radioactive molecular ions (RMIs) from radioactive ion beams (RIBs). Functionally, the IRC accepts a RIB produced upstream by the isotope separation on-line (ISOL) method, decelerates it to eV energies for production of the RMIs and then re-accelerates RMIs to their incident energy. This system promises to form a highly versatile source of complex inorganic or organic RMIs that can be used in fundamental symmetry studies or as precursors to new radiopharmaceuticals. We discuss the challenges of transferring ions from a RIB into a gas cell at room temperature while constraining ions within the RFQ energy well, and of reforming a beam from synthesized RMIs. Factors influencing ion dynamics and reactivity in thermal and non-thermal zones inside the IRC are considered, using results obtained recently with the Isobar Separator for Anions, an analogous RFQ technique used in Accelerator Mass Spectrometry, to illustrate key points.

A Cold Electron-Impact Ion Source Driven by Laser-Induced Electron Emission – New Opportunities for Radioactive Molecular Beams? (Radioactive ion beams, charge breeders and polarized beams)

• Jochen Ballof (CERN)

The thick-target ISOL (Isotope mass Separation OnLine) method provides beams of more than 1000 radionuclides of 74 elements. The method is well established for elements with sufficiently high volatility at up to ca. 2000 C. To extract elements with high melting or boiling points, the formation of a volatile molecule is required. While successful in some cases (e.g. carbon or boron), most of these elements are not yet available as ISOL beam. A variety of volatile carrier molecules has been proposed for all elements produced in the target material [1], but their probability of survival during the extraction and ionization process is often limited by the high temperatures required for isotope diffusion in the thick targets and for ion source operation [2]. While cold target concepts have already been proposed [3], the normal mode of operation of the typically used VADIS (Versatile Arc Discharge Ion Source) with a hot cathode [4] is not well suited. Here we report about first measurements with the electron-impact ion source operated at ambient temperature. Electrons were liberated from the cathode by a laser. While the mechanism of electron production was not yet identified, we propose design parameters for a future photocathode-driven ion source aiming at more than 1% efficiency for the model compound Mo(CO)6. [1] G. Herrmann, Ark Fys, 1967, 36, 111 [2] U. Köster et al, EPJ ST, 2007, 150, 285 [3] J.P. Ramos et al., NIMB, 2016, 376, 81 [4] L. Penescu et al, RSI, 2010, 81, 02A906

CERN’s Hadron Sources: Status and Innovation Overview (Key Technologies for Ion Sources)

• Fredrik John Carl Wenander (CERN)

The CERN accelerator complex is served by several different types of hadron sources, producing both high- and low-intensity negative H- beams, highly charged positive stable ions, but also transforming low-charge radioactive ions to higher charges before post-acceleration. Apart from the operational sources, research and development is carried out at dedicated test stands for H- production and pre-acceleration, ECRIS oven experiments and general EBIS development. In this paper, we will report on the performance and the latest development related to the sources. Efforts to enhance the theoretical understanding of the source physics will be briefly reviewed.

First Beams from the 1+ Source of the ADIGE Injector for the SPES Project (Radioactive ion beams, charge breeders and polarized beams)

• Alessio Galatà (INFN - National Institute for Nuclear Physics)

The ADIGE (Acceleratore Di Ioni a Grande carica Esotici) injector consists of an electrostatic 1+ beam line, equipped with ion sources able to produce a wide variety of beams, coupled to a magnetic beam line, where charge multiplication is accomplished by implementing an Electron Cyclotron Resonance (ECR) based charge breeder. The injector is totally integrated in the SPES (Selective Production of Exotic Species) beam line, to allow the post-acceleration of radioactive ions and is now in an advanced phase of installation. The electrostatic 1+beam line has been put into operation and is now producing beams from alkali metals. This contribution concerns the first results of the beam commissioning of this part of the injector, with the description of the initial debug phase and the solutions adopted to ensure a reliable and continuous operation. Preliminary results of the 1+ beam line characterization will be shown, with a comparison between simulated and measured emittances.

The Design of ITRIP and Progress of Experimental Setup (Production of high intensity ion beams)

• Wei Huang (Institute of Modern Physics)

Highly charged ion sources play an important role in the advancement of heavy-ion accelerators worldwide. Driven by the needs of 100 µs to ms pulsed highly-charged heavy ions for new and existing accelerators, the conceptual design of an Ion Trap for high-Intensity Pulsed beams (ITRIP) was proposed and the proof of principle test has been taken at IMP. The ITRIP is designed to accumulate and convert a CW ion beam into a high-intensity short-pulsed ion beam with suitable compression ratios. Preliminary simulations have been performed and promising results have been obtained. To validate this idea, a test bench has been set up. This paper will present the design of ITRIP. The proof of principle setup as well as the preliminary test results will be specially discussed.

Space Charged Based Residual Ion Beam Recovery for the Neutral Beam Injection (Ion sources for fusion)

• Vincenzo Variale (Universita e INFN, Bari (IT))

Energy recovery of residual ions may be needed to increase the energy efficiency of Neutral Beam (NB) injectors for fusion plants as DEMO while a deflection-based system has been proposed up to now to dump residual ions. As an alternative, a compact beam energy recovery system, based on space charge effects due to the residual ion deceleration into 2 Farady Cups (FC) with holes for D0 passage, can replace the Electrostatic Residual Ion Dump (ERID) designed for ITER and DDT projects to dump the residual D- and D+ before the NB injection in the tokamak plasma. All parameter tunings and simulation are here described, also providing the suppression of backstreaming to the ion source. Ion energy spread Ed and rectangular geometry are considered. Collection of ions at low energy (a few percent of the full neutral beam energy Ki) instead of Ki as in ERID gives advantages that will be discussed.

High Power Density Beam Measurement of the Single Beamlet Multi-Grid Prototype H- Negative Ion Accelerator (Negative ion sources)

• Glynnis Mae Saquilayan (National Institutes for Quantum and Radiological Science and Te)

This paper reports the first emittance measurement of the 160 MW/m2 high power density negative ion beam at target perveance condition of the ITER accelerator. Previously, the ITER requirement on grid heatloads at <5\% of the total acceleration power has been achieved but the aperture edges has been damaged limiting long pulse acceleration. To solve this issue, thermal imaging on 1D-CFC tiles was newly developed to simultaneously measure both profiles and emittances of high power density beams and investigate the overall beam parameters for a single-beamlet. As a result, unknown divergent components up to 10mrad comprise >2\% of the total beam current, which can scrape the electrode apertures, was experimentally identified for the first time. However, it was found that the divergent components were within the acceptance loads of the ITER beamline. These measurement results for the single beamlet contributes to future multiple-beam analysis and design of the ITER accelerator and beamline.

Research and Development of RF Based Negative Ion Source Prototype for CRAFT NNBI (Ion sources for fusion)

• yahong xie (chinese academy of sciences)

A radio frequency (RF) based negative ion source was designed for the The Comprehensive Research Facility for Fusion Technology (CRAFT) NNBI system. In order to understand the physics and pre-study the engineering problems, a prototype source with single driver and a three electrons accelerator was designed and developed. Furthermore, a negative ion source test facility were developed in the same time. On the test facility, the negative ion source prototype was tested with RF plasma generation, negative ion production, extraction and acceleration. The long pulse plasma generation with 1000 s was tested and achieved firstly. Then the negative ion production was tested without and with Cs injection. Finally, the long pulse of negative ion beam extracted and acceleration with 100s was tested successfully. It lays good foundation for the R&D of negative ion source for CRAFT NNBI system.

Redefining Plasma Chambers for ECR Ion Sources: the IRIS Structure (Production of highly charged ion beams)

• Giuseppe Torrisi (INFN - National Institute for Nuclear Physics)

One possible way to optimize microwave coupling and plasma confinement in ECR Ion Sources is a revolutionary design strategy of plasma chambers, breaking the cylindrical symmetry. This contribution reports about the design and numerical validation of an innovative resonant cavity playing as plasma chamber of ECR ​​ion sources. The new chamber, named IRIS (Innovative Resonators for Ion Sources), was argued starting from the 3D structure of the plasma and, therefore, fashioned to the twisting magnetic structure. The microwave launching scheme was radically changed as well, consisting of side-coupled slotted-waveguides with diffractive apertures smoothly matching the overall structure of the camera. This approach also enables a profound optimization of cooling systems and overall spaces in general (for gas feedings, oven systems, sputtering, etc.). Here we report on the conceptual study, electromagnetic design and PIC simulations of the electron heating in the novel resonant cavity, comparing results with those for standard (cylindrical) chamber, and also considering the impact of microwave feeding led by single aperture rectangular waveguides vs. waveguide-slotted antennas. Manufacture strategy, based on additive manufacturing techniques, will also be discussed.

Progress on the Development of Key Technologies for the 4th Generation ECR Ion Source FECR (Key Technologies for Ion Sources)

• Wang Lu

A 4th generation ECR ion source FECR is under development at IMP. Aiming to be operated with the microwave power of 20 kW at 45 GHz, FECR is equipped with a fully superconducting Nb3Sn magnet and conventional parts durable for high power ECR plasma heating and optimum for intense beam production and extraction. Breakthroughs on the Nb3Sn superconducting magnet, high power density plasma chamber, high temperature oven, and so on have been successfully demonstrated recently. The prototype Nb3Sn cold mass has been successfully tested. The plasma chamber with an innovative structure of micro-channel cooling structure has been tested which enables the SECRAL-II ion source operated continuously for more than 1,100 hours with ~300 eμA Kr26+ for routine operation. A high temperature inductive heating oven has also been developed and used for intense uranium beam production. This talk will present the recent progress on the development of key technologies for the 4th generation ECR ion source.

SEISM: 60 GHz ECR Ion Source for Future Accelerator (Production of high intensity ion beams)

• Thomas ANDRE (CNRS-LPSC)

SEISM is a unique ECR ion source operating at a frequency of $60~\textsf{GHz}$. The prototype is based on a simple magnetic geometry, the CUSP, allowing the use of polyhelix coils (developed with LNCMI, Grenoble) to generate the closed ECR surface at $2.1~\textsf{T}$. The plasma is sustained by a high intensity HF pulse (up to $300~\textsf{kW}$). Previous experiments at LNCMI have successfully demonstrated the establishment of the nominal magnetic field and the extraction of ion beams with a current density of up to ~ $1\textsf{A }/ \textsf{cm}^{2}$. The presence of "afterglow" peaks was also observed, proving the existence of ion confinement in a CUSP ECR source. An experimental campaign will be carried out in 2021 using a new transport line designed to improve the transmission of the beam to the new detectors. Recent experimental results as well as short and long-term research plans should be presented to transform this high current density into a high intensity ion beam that can be used for accelerators of the future.

Towards Uranium Intensities Required for FAIR (Production of high intensity ion beams)

• Aleksey Adonin (GSI Helmholtzzentrum für Schwerionenforschung GmbH)

The Facility for Antiproton and Ion Research (FAIR), which is currently under construction at GSI accelerator center (Darmstadt, Germany), will provide wide opportunities for various scientific research programs in different branches. One of the key-elements for future FAIR experiments is uranium. After a commissioning phase it will be required up to 5∙10¹¹ of U28+ ions per pulse at the energy of up to 2 GeV/u. For ion sources this requirement means that it will be necessary to provide 23 emA of U4+ ions at an energy of 2.2 keV/u inside an emittance of 220π mm∙mrad in front of the RFQ (Radio Frequency Quadrupole) with a repetition rate of 2.7 Hz. Vacuum arc ion source VARIS is used for production of high current uranium ion beams at GSI. Recent investigations on increasing of uranium beam brilliance and operational repetition rate of the VARIS as well as test results of various approaches will be described in this work. Another important aspect is high ion beam losses between the ion source and RFQ due to non-optimized post-acceleration system and a beam transport line. Recently these losses are above 75%. To reduce the beam losses for uranium as well as to increase availability of high current beams of other elements it is planned to construct a new ion source terminal dedicated for uranium operation (terminal West). It will be equipped with enhanced post-acceleration system as well as with dedicated straight beam transport line optimized for U4+ ion beams.

Improvement of LAPECR3 Reliability for HIMM Long Term Continuous Operation (Applications and related technologies)

• Jiaqing Li

LAPECR3 ion source had been developed as the ion injector of Heavy Ion Medical Machine (HIMM) accelerator facility since 2009 year. The first HIMM demo facility was built in Wuwei city in 2015, and the facility had been officially licensed to treat patients in early 2020. More than 300 patients have been treated after about one year. In order to further improve the reliability of LAPECR3 ion source for long term operation, continuous research and development work has been made. For instance, a moveable and small diameter bias disc was designed as a microwave tuner to optimize plasma status, a shield ring was adopted prevent main ceramic insulator contamination caused by secondary particles. Moreover, afterglow mode has been considered as the routine operation regime to obtain higher beam intensity at the synchrotron injection and to extend lifetime of the ion source. This paper will introduce the improvement of LAPECR3 ion source and present the latest results of LAPECR3 ion source.

A Few ECRIS Developments at LBNL (Production of highly charged ion beams)

• Daniel Xie (Lawrence Berkeley National Laboratory)

In addition to the ongoing investigation of bremsstrahlung radiation produced by energetic electrons in the superconducting ECR ion source VENUS, the LBNL ion source group has pursued several other research topics since 2015 to explore potential advancements of ECR ion sources. Three of these activities are investigations into the benefits of non-cylindrical plasma chambers, the development of new high-temperature ovens that will efficiently produce the intense, metallic ion beams necessary for superheavy element production at the 88-Inch Cyclotron facility, and the finalization of the conceptual and engineering design of the superconducting NbTi magnet structure for the 4th generation, 45 GHz ECR ion source MARS-D. This article summarizes and briefly discusses the highlights of these ECRIS developments.

Recent Developments and Results of the LPSC PHOENIX Type ECR Charge Breeder (Radioactive ion beams, charge breeders and polarized beams)

• Julien ANGOT (CNRS)

Four models of the PHOENIX ECR charge breeders were manufactured for ISOL application. Two are currently under operation at TRIUMF (ISAC) and GANIL (SPIRAL 1) while the SPES one is being installed on the facility. The last model is set on the LPSC 1+n+ test bench where a R&D program is ongoing to improve its performances. The last modifications consisted in improving the beam line vacuum and the devices alignment. Qualification experiments showed an improvement of the charge breeder performances for all the tested species. In parallel, the charge breeder plasma was studied injecting short pulses of 1+ ions and using a zero-dimension model to estimate some plasma parameters. Comparative measurements done in pulse mode before and after the upgrade allowed a better understanding of the performance improvement. The last R&D program step of the LPSC Charge Breeder together with the experimental results will be presented.

Cesium Balance of the ISIS H- Penning Ion Source (Negative ion sources)

• Olli Tarvainen (STFC Rutherford Appleton Laboratory)

The ISIS Penning ion source is a cesiated pulsed DC discharge surface plasma source delivering 55 mA beam of H$^-$ ions in 250 μs pulses at 50 Hz pulse repetition rate. The constant H$^-$ output, i.e. <5% change, at constant discharge current implies that the cathode work function remains nearly unchanged during the beam current pulse in a wide range of cesium pressures and electrode temperatures. We have developed a model predicting the equilibrium cesium coverage of the cathode (in eV) and the expected H$^-$ beam current (in arb. units). The model is based on semi-empirical expressions for the cathode work function, negative ion surface ionization yield, and cesium adsorption and desorption rates. We compare the model predictions to experimental data. It is concluded that the ISIS Penning ion source operates near the optimum cathode work function in a wide range of cesium pressures and cathode temperatures. The implications of the cesium balance on long pulse operation are discussed.

Plasma Commissioning in a High Power External Antenna RF-driven Volume-type H- Ion Source (Negative ion sources)

• Scott Lawrie (UKRI/STFC/RAL)

A high power, high duty cycle, negative hydrogen ion source is in development at ISIS. It will operate in pure volume-production mode and is driven by a 6½-turn solenoid antenna mounted external to the plasma chamber. A solid-state amplifier with a maximum output of 100 kW in 50 Hz, 1 ms pulses delivers RF power to the antenna via an impedance-matching network. The amplifier has a relatively wide bandwidth, able to deliver full power from 1.8-4.0 MHz. This flexibility allowed straightforward commissioning of the matching network into an inductively-coupled plasma. Striking of the pulsed plasma is facilitated by a compact microwave ignition cavity requiring only 10 W of power at 2.45 GHz to deliver 1 mA seed pulses of electrons. Experiments have shown that it is vital to encapsulate the RF antenna properly to mitigate high voltage sparking. In addition, the location of the antenna relative to the ion source’s permanent magnets has a critical effect on the ease of plasma ignition.

Sustainability Issues and Improvements in Long-Term Operations with Negative Hydrogen Ion Sources for Particle Accelerators (Negative ion sources)

• Robert Welton (Oak Ridge National Laboratory)

High brightness, negative hydrogen ion sources are used extensively in many scientific facilities operating worldwide. Negative hydrogen beams have become the preferred means of filling circular accelerators and storage rings. Several facilities now have long-term (>several years) experience with operating a variety of these sources (RF, filament, magnetron and penning) and have encountered, and in some cases solved, performance limiting issues. A representative list of such facilities includes, the US Spallation Neutron Source (SNS), Japan Proton Accelerator Complex (J-PARC), Rutherford Appleton Laboratory (RAL-ISIS), Los Alamos Neutron Science Center (LANSCE), Fermi National Accelerator Laboratory (FNAL), CERN LINAC-4 and numerous installations of D-Pace ion sources. This report summarizes key ion source sustainability issues encountered at these facilities and discusses how some of them are being addressed through recent source improvements.

Cesiation of RF-Driven Negative Hydrogen Ion Source for the Upgrade of China Spallation Neutron Source (Negative ion sources)

• Weidong Chen (Institute of high engery physics, Chinese academy of sciences.)

An RF driven negative hydrogen source is under development for the upgrade of China Spallation Neutron Source (CSNS), which requires an H$^-$ beam current more than 50 mA, and a duty factor of 1.5%$\sim$2%. The ion source produces an H$^-$ beam of 20 mA without cesium injection. After it is cesiated, more than 60 mA H$^-$ beam is extracted. The emittance of the ion beam is measured both with a double-slit scanner and a pepper-pot device. It gives a normalized root of mean square emittance of about 0.4 $\pi\cdot$mm$\cdot$mrad at a beam current of 40 mA, which is much lager than the acceptance of Radio-frequency Quadruple (RFQ) accelerator located downstream. To find the reason, the magnet field distribution of the extraction system is measured. Based on the measurement, the trajectories of the H$^-$ beam and the co-extracted electron beam are simulated with CST program.

Difference of Co-Extracted Electron Current and Beam Acceleration in a Negative Ion Source with Hydrogen-Isotope Ions (Ion sources for fusion)

• Katsunori Ikeda (National Institute for Fusion Science)

Improvement of the performance on a hydrogen/deuterium negative ion source for a nuclear fusion device are reported. In particular, the suppression of the co-extracted electron current, $I_{e}$, is an important issue to ensure the stable beam acceleration. Improvement of the $I_{e}$ has been confirmed by optimizing the magnetic field of the electron deflection magnet in the extraction grid. The mismatch of beam deflection angle will be verified in 2021. Other two methods for reduction of the $I_{e}$ were validated. First method is an outer iron yoke. The ratio of the $I_{e}$ to the deuterium negative ion current, approximately $I_{e}/I_{acc}$ decreased by 0.1 compared with that in hydrogen. Second method is an electron fence (EF) whose rods are set between the rows of apertures on the plasma grid. The $I_{e}/I_{acc}$ was greatly improved from 0.7 to 0.25 in deuterium. These attempts have improved the total deuterium injection beam power of 8.4 MW by three negative ion based NBIs.

Reverse Trajectory Analysis of the Hydrogen Negative Ion Beam in a Prototype Accelerator for ITER (Ion sources for fusion)

• Masashi Kisaki (National Institutes for Quantum and Radiological Science and Te)

The hollow meniscus shape in the multi-stage MeV-class accelerator for ITER was identified for the first time by the reverse trajectory calculation with the measured emittance. The molten traces due to the power deposition of the negative ion beam, which was not predicted by conventional particle tracking codes, were observed on the edge of a grounded grid after long pulse operation in a prototype accelerator for ITER. Because such unexpected damage to the grid is a critical issue for the ITER accelerator, a reconstruction of the beam trajectory has been tried by iteratively calculating the beam trajectory backward from the measured emittance profile to the meniscus. As a result, it was found that the negative ion is mainly extracted from the periphery of the extraction hole. This led to deformation of the meniscus and degradation of beam focusing, resulting in the local grid heat load by the negative ion beam. This finding contributes to the design optimization of the ITER accelerator.

Study of Negative Ion Based Injector Prototype at Budker Institute of Nuclear Physics (Ion sources for fusion)

• Oleg Sotnikov (Budker Institute of Nuclear Physics )

A high-voltage neutral beam injector, based on the acceleration of a negative hydrogen ion beam is under construction at the Institute of Nuclear Physics [1]. In contrast to the traditional scheme of the multiaperture negative ion source attached to the multiaperture accelerator tube it uses an original scheme with the single-aperture accelerator spaced apart from the multiaperture ion source. The vacuum tank with LEBT section, containing the beam bending magnets and vacuum pumps is introduced between the ion source and accelerator. It permits to purify the accelerated negative ion beam from the gas, secondary particles and residual cesium flows from the ion source to accelerator, and to prevent the ion source illumination by secondary particles from accelerator. The experiments on negative ion beam production, transport and acceleration were produced at the BINP HV test stand, consisting of ion source, LEBT tank, acceleration tube and HEBT with calorimeter. An efficient acceleration of negative ion beam to energy up to 330 keV were produced at the BINP test stand recently. The data on 1A negative ion beam production, its transport through the LEBT, acceleration with the single-aperture acceleration tube and following transport to the distance ~ 10 m from the source will be presented. The data on the beam transport to distances 2.5 m, 4.5m and 10m vs various source parameters will be described. [1]. A.A. Ivanov, et al. AIP Conf. Proc. 1515, 197 (2013)

Towards the Optimization of the Cs Evaporation Configuration for Long Pulse Operation of Negative Ion Sources (Ion sources for fusion)

• Alessandro Mimo (Max-Planck-Institut für Plasmaphysik)

Negative ion sources for neutral beam injection rely on surface production of negative ions on a caesiated low work-function surface (plasma grid). To maintain the low work function in long pulses (one hour) and the desired source performance (extracted H-/D- ions and limited co-extracted electrons), Cs needs to be constantly delivered onto the plasma grid. The CsFlow3D code was applied to the ELISE source to simulate the evaporation and the plasma-assisted redistribution of Cs. The Cs flux stability is investigated for consecutive one hour plasma pulses and compared with experiments. Three methods to optimize the Cs evaporation are simulated: by adjusting position and orientation of the Cs evaporator and by using a distributed Cs evaporation concept, either on the back-plate of the source or close to the plasma grid. An increase of the Cs flux occurs for all three methods, while the best control and lowest Cs consumption is obtained by the direct evaporation close to the plasma grid.

Effect of RF Electric Field on Beam Focusing in Negative Ion Source Plasma (Ion sources for fusion)

• Taiga Hamajima (Nagoya University)

Optimization for beam focusing of negative ions is one of the important issues for developing neutral beam injector (NBI) for ITER. Low beam divergence less than 5 mrad has been realized with Filament-Arc (FA) type negative ion sources. On the other hand, the divergence with Radiofrequency (RF) type sources is over 2 times larger than that obtained with FA sources, and the ITER requirement on the divergence less than 7 mrad has not been achieved so far. In this study, the beam focusing is investigated when the RF electric field is externally applied in the beam extraction region of the FA source (NIFS-RNIS). A RF antenna is installed in the beam extraction region, and the RF electric field with a frequency range of 4-8 MHz is applied. A beamlet shape is measured, and the responses of beamlet width and beamlet axis position to the RF field are experimentally observed. It is found that the beam focus of negative ions is deteriorated with the RF electric field.