High Current Ion Source Research Articles

Status of the High-Current Electron-Beam Ion Source Charge Breeder for the Facility for Rare-Isotope Beams

The Reaccelerator (ReA) of the Facility for Rare-Isotope Beams (FRIB) employs an Electron-Beam Ion Trap (EBIT) as a charge breeder to reaccelerate rare-isotope beams up to 12 MeV/u. The ReA EBIT produces an electron current of 300 – 600 mA. The maximum trap capacity of the ReA EBIT is 1010 elementary charges. FRIB production rates are expected to exceed 1010 particles/s in some cases in the future. There is also a user demand for reaccelerated stable-isotope beams of more than 1010 pps. To handle these rates and provide redundancy, a High Current Electron-Beam Ion Source (HCEBIS) has been built and is now being commissioned. An electron-beam current of 2 A with a 50 % duty cycle has been transported through a 4-T field. An upcoming upgrade to increase the electron-beam current up to 4 A will allow for a maximum trap capacity of 2.4×1011 elementary charges. We present the status of the HCEBIS, including the results of the electron-beam commissioning and systematic studies.

High current positive ion source for Copernicus NBI based on a cold-cathode arc plasma generator

The NBI system based on positive ions to be applied for TAE’s next-generation field reversed configuration experiment, Copernicus, has been designed. The beamlines are longer in the new system, so the required beam divergence smaller relative to the NBI system on TAE’s current device. This requirement motivates a change from slot-shaped apertures to circular in the plasma grid. The influence of changing the aperture shape on the divergence and total beam current across the extraction area has been examined. When considering spatial uniformity in calculations, it is expected that a beam current value of 173 A and a beam divergence angle of 17 mrad will be achieved, exceeding the required values by 15%. An octagonal-shaped ion source has also been developed for a future upgrade targeting 2.5 s long pulse operation, and the estimation indicates 83% source plasma uniformity with concurrent suppression of thermal loads. The development of multiple plasma diagnostics for assessing uniformity and proton ratios has been completed to validate these estimations and optimize the ion source dimensions.

High-Current Capability and Upgrades of the EBIS/T Charge-Breeding System in the Reaccelerator at the Facility for Rare-Isotope Beams

The Reaccelerator (ReA) of the Facility for Rare-Isotope Beams (FRIB) at Michigan State University uses a Beam Cooler/Buncher (BCB) and an Electron-Beam Ion Trap (EBIT) as a charge-breeding injector system. The rare isotopes produced by In-flight Separation are selected by the Advanced Rare Isotope Separator (ARIS) and stopped in a helium gas cell. Long-lived and stable-isotope beams can also be extracted from a Batch-Mode Ion Source (BMIS). The continuous beams transported at low energy to ReA are injected into the BCB. The pulsed beams are then injected into the EBIT, charge bred, ejected, and accelerated by ReA’s LINAC. The EBIT electron current (300 - 600 mA) is a factor that limits its capacity to ∼2×1010 elementary charges, which restricts the maximum EBIT-extracted rates to less than 2×1010 particles per second for light ions. An upgrade of the EBIT electron gun is expected to provide 2 A in current. In parallel, a High-Current Electron-Beam Ion Source (HCEBIS) is being commissioned. The HCEBIS can presently provide an electron current of 2 A. An upgrade will increase the current to 4 A. The implementation of these two upgrades is expected to allow for maximum rates to be ∼1011 pps, compatible with FRIB projected rates and user demands. We review the high-current capabilities and upgrades of ReA’s charge-breeding system.

Characterization of a broad beam ion source converted into a high intensity deuterium beam

Avalanche Energy is developing deuterium ion beams for the Orbitron fusion device. For these and similar projects, modification of off-the-shelf high current ion sources enables affordable and rapidly accessible alternatives to custom-built systems. We have successfully operated the Veeco MARK I broad beam source on deuterium to create multi-keV energy ions. Directing this beam through a small aperture required carefully designed optics. Once a narrower beam was created, a faraday cup was used to measure the beam current and profile while a Thomson Parabola was developed to help understand the beam species and energy composition.

Modular NBI heating system with high current microwave ion source for fusion reactors

The neutral beam injection system is identified as one of the main options for plasma heating methods in nuclear fusion reactors. The heating system is useful for reaching the nuclear fusion reactions in a high-rate regime. In this regard, the size of the devices is an important challenge in the design and construction of these systems.In this paper, a modular neutral beam injection heating system is represented for the fusion reactors. This novel NBI system can produce an energetic neutral beam with a low divergence angle. A microwave plasma source is employed for the generation of the high-density plasma. It is found that the plasma source can provide a proper density of the plasma for the extraction of a positive ion beam with a high current. Using COMSOL software, the microwave plasma source with optimal frequency at a power of 500 W is designed and simulated for each heating module. In addition, an extractor system is designed and simulated to extract an ion beam with an optimal current of 190 mA from the plasma source in each module, where the three-electrode configuration is used in the extractor. It is found that to reach the positive ion beam current, 25 apertures with a radius of 1.5 mm are needed for electrodes. As a result, a beamlet with a minimum RMS divergence angle of about 20 mrad and maximum perveance of 1.2×10−8A/V3/2 can be extracted by each aperture. In this regard, the modular neutral beam injection system with the power of 30 KW (for a small size tokamak), a beam energy of 4.5 keV, a total cross-section of 385 cm2, and 40 heating modules is designed and simulated. This work indicates that; this modular heating system not only reduces power consumption but also solves the problem of space consumption.

Progress of the High-Current EBIS Charge Breeder for the FRIB

The ReA post-accelerator of the National Superconducting Cyclotron Laboratory employs an Electron-Beam Ion Trap (EBIT) as a charge breeder to reaccelerate rare-isotope beams to several MeV/u. The Facility for Rare-Isotope Beams (FRIB) is near completion and will provide RIB rates expected to exceed in some cases 1010 particles/s. The ReA EBIT operates with an electron current of 300 – 600 mA, corresponding to an electron current density of 170 – 340 A/cm2 and a maximum trap capacity of 1010 elementary charges, which can be insufficient to handle high FRIB rates. A High-Current Electron-Beam Ion Source (HCEBIS) has been constructed based on the backbones of the TEST EBIS from the Brookhaven National Laboratory. By using a 4-A electron beam, a current density of 298 A/cm2 and a maximum trap capacity of 2.4×10n elementary charges can be achieved. This paper presents the status of the HCEBIS. It also includes results of electron- and ion-beam simulations and discusses electron-beam commissioning plans.

Analysis of the chemical network in a volume-production high-current negative hydrogen ion source

Complex simulations (e.g. multi-dimensional fluid models) usually prevent the use of very large chemistry models. In this work, the important physicochemical processes in a volume-production high-current negative hydrogen ion source (HCNHIS) are identified for a pressure range of 1–100 Torr using a global model. The particle species include H2(υ = 0–14), H(n = 1–3), , , H+, H−, and electrons. The simulation results indicate that for the production of negative hydrogen ions through dissociative attachments, the high vibrational levels of hydrogen molecules are important at low pressures, and the ground state and low vibrational levels of hydrogen molecules play an increasingly important role with increasing pressure. The reactions involving the ground state, low vibrational levels, and neighboring levels of each level tend to dominate the production of vibrational levels and transitions between them in the volume-production HCNHIS. With increasing pressure, the electron energy dissipation shifts from dissociation of H2(υ = 0) and electron excitation of H2(υ = 0) through an indirect mechanism followed by radiative decay (the EV process) to electron excitation of H2(υ = 0) through a resonant mechanism (the eV process). A valuable subset of reactions provided by the simplified model is proposed in the investigated pressure range, which could be incorporated in more complex simulations. The results obtained with the simplified model under different simulation conditions are within an acceptable error margin of the results for the full model, which indicates that the robustness of the simplified model of chemical reactions is guaranteed to some extent.

A Band Rejection Filter of High Current Radio Frequency Ion Source for Neutral Beam Injector

As a promising ion source, the radio frequency (RF)–driven ion source is widely equipped in the neutral beam injector of magnetic-confinement fusion devices. In order to study the characteristics of the RF-driven ion source and plasma generation, a prototype RF negative ion source–based test facility has been developed at the Institute of Plasma Physics, Chinese Academy of Sciences. Many diagnostic tools have been developed for this test facility. The electrostatic sensors are a critical part of the diagnostic methods. Considering the electrostatic sensors to be used in the harsh RF environment, an improved RF compensation circuit [band rejection filter (BRF)] has been developed that effectively reduces RF interference and improves signal acquisition accuracy. The BRF has been successfully verified for frequency response characteristics in a magnitude plot.

Status of a point-like neutron generator development

In this paper we report on a high current density ion beam profile diagnostics with a slit-based system as a reliable method, capable of high thermal load applications. The task arose in frames of a point-like neutron source development for neutron radiography. In previous research, it was suggested to construct such a system as a D-D neutron generator based on the high current gasdynamic ion source, which utilises the plasma of electron cyclotron resonance discharge sustained by powerful millimeter wave gyrotron radiation. This device is able to produce focused D+ beams with a characteristic diameter of 1 mm, total current above 100 mA, and current density at a level of several A/cm2. Study of such intense beams profile to obtain the best focusing efficiency and minimize neutron producing area appeared to be a challenging task. The paper also demonstrates the possibility of fast neutron imaging with a point-like powerful neutron generator (neutron yield on the level of 1010 s−1).

LINAC developments for heavy ion operation at GSI and FAIR

The first cavity of a standalone superconducting (sc) continuous wave (cw) heavy ion Linac as a demonstration of the capability of 217 MHz multi gap Crossbar H-mode structures (CH) has been already commissioned at high acceleration gain. The worldwide first beam test with a superconducting multi gap CH-cavity was a milestone of the R&D work of HIM and GSI in collaboration with Goethe University Frankfurt (GUF) in preparation of the sc cw heavy ion Linac project, substituting GSI-UNILAC as a heavy ion high duty factor Linac. Recently the first two of four fully equipped cw-Linac cryomodules are in procurement. To meet the future FAIR science requirements higher beam intensity has to be achieved in the present GSI-accelerator complex. In the last years ion source developments, in particular for the high current Vacuum Arc Ion Sources (VARIS), were concentrated on heavy elements, as Bi and Pb, aiming for stable routine ion source operation at a sufficient rep. rate and high production efficiency. Stripping is a key technology for all heavy ion accelerators. After upgrade of the supersonic N2-gas jet implementation of high current foil stripping, recently a new H2gas cell, using a pulsed gas regime synchronized with arrival of the beam pulse has been developed. An enhanced stripper gas density as well as a simultaneously reduced gas load results in an increased stripping efficiency, while the beam emittance remains the same. A new record beam intensity (11.1 emA) for238U28+beams at 1.4 MeV/u has been achieved, applying the pulsed high density H2-stripper target to a high intensity238U4+beam from the VARIS ion source. Further ion source developments have been accomplished recently providing for sufficient heavy ion beam intensities at the High Current Injector Linac. A machine investigation program has been performed in 2020. The focus was to optimize the entire FAIR injector chain for high intensity heavy ion beam after the successful implementation of different upgrade measures. Besides a dedicated operation mode applying UNILAC, as a heavy ion Linac, at a synchronous phase significantly lower than 30 degrees for high intensity proton beam, could be established. Thus, UNILAC is able to deliver a sufficient proton beam intensity for the FAIR commissioning phase, when the FAIR-proton Linac is not yet available.

A slit-based method of a high-current ion beam transversal distribution diagnostic

This article presents the results of experimental studies that are part of the research aimed at the development of a point-like neutron source for fast neutron tomography. In frames of the used approach neutrons are produced in D-D fusion at the deuterium-loaded target bombarded with the focused deuterium ion beam. It was proposed to use a high-current ECR ion source to obtain the ultimate beam intensity at the target and maximize the neutron density yield. An important parameter of the neutron source is the size of the emitting region, which, in turn, is determined by the quality of the ion beam focusing. The presented work is dedicated to the development of the diagnostic system able to measure the ion beam transverse distribution. This system is based on the movable plates with orthogonal slits as an alternative to previously used scintillator-based method. The proposed system allows to determine the high-current deuterium ion beam size with an accuracy higher than 1 mm. This work presents verification of the previously obtained results of the high current focused deuterium ion beam formation by means of a slit-based method reliable in measuring beams of high intensity.

Magic Clusters PtMg2,3 H5 - Facilitated by Local σ-Aromaticity.

The concept of local aromaticity has been successfully utilized in understanding the stability of certain atomic clusters. However, all the skeleton atoms in these clusters are covered by at least one local aromatic feature, collectively making the multiple local aromaticities coexist globally. Herein we show the robustness of local aromaticity as a tool for the discovery of novel magic clusters: not all of the skeleton atoms need to be covered by an aromatic feature to make the cluster magic. In this study, the PtMg2,3 H5 - cluster anions are generated by a unique high-current pulsed discharge ion source and found to be magic numbers using mass spectrometry. Photoelectron spectroscopy and calculations confirm that only the PtH4 2- kernels in these clusters are locally aromatic. Based on these results, we propose that local aromaticity can be gainfully utilized as a new potential magic rule in the search for magic numbers.

A powerful pulsed “point-like” neutron source based on the high-current ECR ion source

The paper presents recent results of a "pointlike" neutron source development based on a D-D fusion in a D-loaded target caused by its bombardment with a sharply focused deuterium ion beam. These developments are undergoing at the Institute of Applied Physics of Russian Academy of Sciences in order to study a possibility to create an effective and compact device for fast-neutron radiography. The last experiments with a beam produced by a gasdynamic high-current ECR ion source and its focusing with a magnetic lens demonstrated that 60 mA of deuterium ions may be constricted to a transversal size of ∼1 mm at the focal plane. With a purpose to improve this result in terms of the beam current and its size, a combined electrostatic and magnetic focusing system is proposed and analyzed. It is shown that the combined system may enhance the total beam current and reduce its footprint down to 0.13 mm. All numerical analysis was performed using the IBSimu code.

Development of a regenerated Beryllium target and a thermal test facility for Compact Accelerator-based Neutron Sources

Recently, the possibility to use compact accelerators coupled to high current ion sources for the production of intense low energy proton or deuteron beams has motivated many research laboratories to develop accelerator based neutrons sources for several purposes, including Neutron Capture Therapy (NCT). The NCT needs a high flux, about 10 9 n.cm-2.s-1, of thermal neutrons (E<10 keV) at the tumour site. Up to now, the NCT required neutron flux was mainly delivered by nuclear reactors. However, the production of such neutron flux is now possible using proton or deuteron beams on specific targets able to stand a high pow er (~15- 30 kW) on a small area (~10 cm2). This specific target design, materials and supports, has to cope with extreme physical constraints . The LPSC team has conceived an original solution formed by a thin (8 μm) rotating beryllium target depos ited on a graphite wheel and coupled with a beryllium sputtering device for periodic 9Be layer restoration. By means of 9Be (d,n) 10B nuclear reaction, this target irradiated by a 10- -20 mA deuteron beam (1.45 MeV) should produce the required neutron flux. In order to validate the target design of the neutron flux production and the beryllium target thermal capabilities, we built a 30 cm diameter rotating Beryllium target prototype and a compact electron beam line able to deliver a power density of 3kW/cm2.

Structure design and analysis of RF ion source for negative ion source test facility.

A negative ion source acts as a critical part in a neutral beam injector (NBI). A high current ion source is required for the high-power NBI. In this paper, a prototype radio frequency (RF) ion source and its test facility are developed in the Institute of Plasma Physics, Chinese Academy of Sciences, to demonstrate the key technology of the high power negative ion source. The structure design of the RF negative ion source is presented, involving the designs of the ion source plasma generator and accelerator. The detailed structure design and analysis of the key parts of the ion source are also presented, such as the Faraday shield (FS) and accelerator grids. The fluid-thermal-structural coupling characteristics of the FS and grid are explored with different mechanisms of fluid pressure, RF power, and the structure type on the thermal stress. Then, the processing and manufacturing scheme of the FS and grids are also given. Finally, the results were presented with a manufactured three cooling channel FS. The experimental results prove that the developed structure design of the RF ion source is effective and reliable, and the correctness of finite element analysis is also verified by experimental data comparison.

High-Current Pulsed ECR Ion Sources

At the present time, some ECR ion sources use a high-frequency powerful microwave radiation of modern gyrotrons for plasma heating. Due to high radiation power, such systems mainly operate in a pulsed mode. This type of ECR ion sources was developed at the Institute of Applied Physics of the Russian Academy of Sciences (IAP RAS), and most experimental research was performed at the SMIS 37 facility, at which 37 gyrotrons with 37.5- and 75-GHz frequencies and 100- and 200-kW maximum powers, respectively, were used for plasma production. Such heating microwaves allow creating plasma with unique parameters: electron density >1013 cm–3, electron temperature of 50–300 eV, and ion temperature of about 1 eV. The principal difference between these systems and conventional ECR sources is a so-called quasi-gas-dynamic regime of plasma confinement. In accordance with the confinement regime, such sources have been called “gas-dynamic ECR sources.” Typically, plasma lifetime in such systems is about several tens of microseconds, which, in combination with the high plasma density, leads to the formation of plasma fluxes from a trap with a density of up to 1–10 A/cm2. The possibility of production of multiply charged ion beams (nitrogen, argon) and proton (or deuterium) beams with currents of up to a few hundred mA and normalized rms emittance of about 0.1π mm mrad was demonstrated. The next step in the research is a transition to continuous wave operation. For this purpose, a new experimental facility is under construction at the IAP RAS. A future source will utilize 28- and 37.5-GHz gyrotron radiation for plasma heating. An overview of the obtained results and the status of the new source development is presented.

Physical design and evaluation of a high-intensity accelerator-based D-D/D-T fusion neutron source

A high-intensity accelerator-based D-D/D-T fusion neutron source (ZF-400) with a thick adsorption target is designed with an intensity of $ 10^{13}$ n/s. A high-current microwave ion source is used to produce a large current deuteron beam, and neutrons are generated by irradiating the deuteron beam on a deuterium-adsorption target or tritium-adsorption target. According to the particle-in-cell (PIC) code, the length of the whole high-current D+ beam transport line is 500cm, the D+ beam transfer efficiency is up to 96%, and various components can match each other. On the rotating target, the D+ beam spot size is about 20.0 mm with energy of 450 keV. Based on the heat conduction theory, the thick adsorption rotating target with water-cooling can withstand the D+ ions beam with 450 kV/50 mA and ensure that the temperature is less than 200 °C. According to the multi-layer computing model, neutron energy spectra, angular distributions and yields for the thick target can be calculated with remarkable precision. The neutron energy spectra are non-mono-energetic neutrons for the ZF-400 neutron generator, the neutron angular distributions are anisotropic distributions, and they can provide neutrons with an intensity of $ 2.8\times 10^{11}$ n/s (D-D) and $ 1.4\times 10^{13}$ n/s (D-T), respectively, with the deuteron of 450 keV/50 mA.

Ion Angular and Initial Energy Distributions in Arc Discharge Deuterium Ion Source

Ion beams of hydrogen isotopes are of interest for accelerator and surface modification technologies. One of the methods of the generation of hydrogen-isotope ion beams is by using a high-current arc discharge ion source with hydrogen-saturated electrodes. The divergence of an ion beam is determined by the initial energy and angular distributions of ions. Some applications require ion beams with a divergence of 100 mrad or less. This paper analyzes the initial energy and angular distributions of ions in an ion source based on an arc discharge with a deuterated zirconium electrode. The analysis shows that the angular distribution of deuterium ions, compared to zirconium ions, is much broader and that the initial energy of zirconium ions in the ion beam is greater than the initial energy of deuterium ions.

Pulsed neutron generator with a point-like emission area based on a high-current ECR source of deuterium ions

The paper demonstrates a possibility of a high-power compact neutron generator creation with 1010 s−1 neutron yield and small emitting area (about 1mm) based on a high-current ECR ion source with a quasigasdynamic plasma confinement regime. Neutron generation is realized by D-D fusion at deuterium-loaded target bombarded by a sharp focused high-current (50 mA) deuterium ion beam with energy at the level of 80 keV.

Beam extraction characteristics of a low-energy, high-current pulsed ion source of a versatile experiment spherical torus neutral beam injector

A neutral beam (NB) ion source aimed to inject a 0.5-MW NB has been developed for Versatile Experiment Spherical Torus (VEST) plasma heating. Beam energy is generally limited to less than ∼20 keV to reduce particle orbit loss and beam shine-through. To meet this power demand, high-current ion beam extraction is important to achieve the required performance of the ion source. In this study, a 0.7-MW ion source was designed, fabricated, assembled, and optimized at the NB test stand in Korea Atomic Energy Research Institute (KAERI) considering the beam power losses in the beamline components. The ion source comprises a multicusped-bucket-type plasma generator and a multislot-triode-type ion accelerator with an extraction area of 12 cm × 46 cm. The characteristics of arc discharge and beam extraction were investigated using hydrogen gas to obtain the optimum operating parameters of the arc power, filament voltage, gas pressure, extraction voltage, and suppression voltage. The ion source was then conditioned and performance tests were primarily completed. Results of the experiments show that the ion source can extract sufficient ion beam power that is than 0.75 MW (50 A/15 keV) with 100-kW arc power. The arc efficiency and beam perveance were estimated to be 0.6 A/kW and 20–25 μP, respectively. Moreover, the design goal of delivering a 0.5-MW NB into the VEST plasma will be achievable based on the optimum operating conditions. This ion source has been installed in the VEST NB injection system at Seoul National University and its commissioning is ongoing.