Low Energy Beam Transport System Research Articles

Multi-purpose low energy beam transport system for light heavy-ion beam accelerator

The bore diameters of magnets and envelopes of beams in a low energy beam transport (LEBT) system should be large. The large diameter of magnet expands the fringe field as the fringe field distribution depends on the aperture size of the magnet. To avoid magnetic field interference and prevent damage, we investigate the fringe field distribution of a magnet. Further, we present two beam dynamics case studies, wherein all the requirements of a multi-purpose application system using different acceleration modes for neutron generation and implantation are satisfied. Providing energies between a few tens to hundreds of kiloelectronvolts, is an essential apparatus for material science studies in the low energy-region. Considering the fringe field effect of the developed magnets, the LEBT system has been re-designed to satisfy these requirements. We describe the magnetic field distributions in terms of beam dynamics parameters, and discuss it with regard to the two operation modes.

A Low Energy Beam Transport to Match a Multicusp Ion Source to an RFQ

The RadioFrequency Quadrupole Direct Injection Project (RFQ-DIP) uses a filament-driven multicusp ion source to produce . A Low Energy Beam Transport (LEBT) injects the beam from the ion source into the RFQ. The LEBT shapes the beam to the optimum input Twiss parameters for transmission through the RFQ while minimizing the emittance. The LEBT system has been designed using the accelerator codes IBSimu and Warp. To ensure the accuracy of the simulations, a series of diagnostic tools to assess the beam quality have been integrated into the LEBT design. The LEBT also integrates a beam chopper for machine protection and duty factor control, as well as steering capability to compensate for small misalignments. Presented here are the beam dynamics simulations and the design of the LEBT and matching to the RFQ.

Design study of compact medical accelerator using superconducting rf quadrupole for boron neutron capture therapy

We investigated the feasibility on the application of a superconducting radio frequency (SRF) niobium cavity to an accelerator-based neutron source for boron neutron capture therapy (BNCT). Neutron source is the key component of BNCT and adopting rf-linac based neutron source realizes a medical care system sufficient to be compact, which can be installed in a hospital and to generate intensive neutron yields that the BNCT requires. However, it is still desirable to improve the efficiency of input power on neutron yields and the achievable accelerate field gradient. SRF accelerator technology potentially allows us to enhance the performance because of its prominent lower ohmic loss and higher sustainable accelerating fields. This paper presents a first feasibility study on the application of a SRF niobium cavity to an accelerator-based neutron source for BNCT, assuming that a superconducting radio frequency quadrupole (SC-RFQ) composed of pure bulk niobium at 4.2 K accelerates the proton/deuteron beams to a beryllium or lithium target for the neutron production of BNCT via $^{7}\mathrm{Li}(\mathrm{p},\mathrm{n})^{7}\mathrm{Be}$, $^{9}\mathrm{Be}(\mathrm{p},\mathrm{n})^{9}\mathrm{B}$, or $^{9}\mathrm{Be}(\mathrm{d},\mathrm{n})^{10}\mathrm{B}$. The following beam parameters were used: beam energy of 2.5 MeV (for Li target)/5 MeV (for Be target), ion source current (50 keV, CW 30 mA), normalized beam emittance of 0.02 cm mrad, and resonance frequency of 325 MHz (for proton)/162.5 MHz (for deuteron). Based on these conditions, we evaluated the feasibility on the following three criteria: comparison of the cooling capacity of the refrigerator to the amount of heat, power consumption of AC, and size of the BNCT system. First, we evaluated the amount of heat generated in a cryomodule by adding the ohmic loss of SC-RFQ ${Q}_{\mathrm{rf}}$, beam losses in SC-RFQ ${Q}_{\mathrm{b}}$, heat penetration into the cryomodule ${Q}_{\mathrm{ext}}$, and beam losses of molecular ion beams and poor quality beams emitted from the ion-source at/near the RFQ entrance ${Q}_{\mathrm{emit}}$. In this study, we typically regarded ${Q}_{\mathrm{ext}}$ as 20 W at 4.2 K and considered a new low-energy beam transport system that can suppress ${Q}_{\mathrm{emit}}$ to 0. In addition, ${Q}_{\mathrm{rf}}$ and ${Q}_{\mathrm{b}}$ were numerically evaluated by beam simulation and electromagnetic calculation. The obtained results revealed that the sum of the heat amounts could be sufficiently suppressed below the typical cooling capacity of a commercially available helium refrigerator. Second, we compared the ac power consumption of BNCT between a conventional and SC-BNCT systems, which indicated that the BNCT system adopting the SRF cavity effectively reduced the ac power consumption of SC-BNCT by almost $1/4$ times. Third, the length of the SC-RFQ could be shortened by adjusting the peak surface E-field, as compared to conventional existing RFQs such as J-PARC, SNS, and IFMIF. Eventually, this study demonstrated that the application of the SRF cavity for the rf-linac-based neutron source of BNCT is feasible, and thus provides a foundation for the future development of design for next-generation BNCT systems.

Effects of linear quadrupole fringe field overlap on transverse matching to an radio frequency quadrupole

Along many low energy beam transport (LEBT) systems transverse hadron beam matching to a subsequent radio frequency quadrupole (RFQ) is performed by magnetic quadrupole multiplets. Large apertures combined with short distances between the quadrupoles lead to overlap of individual singlet fields and significantly impact on the effective beam optics. Systematic measurements of beam transmission through an RFQ have been done and compared to beam dynamics simulations. For the latter, simplified hard-edge quadrupole fields were replaced by measured field data. It turned out that the hard-edge model is not sufficiently accurate to achieve acceptable agreement between calculated and measured beam properties.

Coherent Smith-Purcell radiation for minimally invasive bunch length measurement at the subpicosecond time scale

We have designed a tool to measure the bunch length of an electron beam in a minimally invasive way by means of coherent Smith-Purcell radiation (SPR). The technique has been employed successfully at a test apparatus for the Mainz Energy-recovery Superconducting Accelerator MESA, demonstrating it is possible to determine the bunch length while losing less than 0.6% of the electron beam. The impact of the space charge on the bunch length can be reduced while tuning the longitudinal bunch preparation system during a live measurement at beam currents up to 1 mA. Doing so, RMS bunch lengths of $70\text{ }\text{ }\ensuremath{\mu}\mathrm{m}$ can be achieved in a typical operating mode of the low-energy beam transport system of MESA. In addition to the bunch length measurements, typical properties of the generated SPR are demonstrated.

Design of compact accelerator system for high flux accelerator based neutron source.

Accelerator Based Neutron Sources (ABNS) have been studied for their utility in materials research as well as for boron neutron captured therapy. By making significant efforts to study the (p,n) and (d,n) nuclear reactions, the specifications of the accelerator system have been determined. In this paper, we compare the design results for two types of radio frequency quadrupole (RFQ) accelerators to provide proton and deuteron beams, respectively. Both systems consist of an electron cyclotron resonance (ECR) ion source, a low-energy beam transport system, an RFQ accelerator, a medium-energy beam transport system, a Be target, and a moderator system. In order to achieve a compact accelerator system at a reasonable cost, different requirements must be applied to the design of RFQ accelerators. The proton RFQ has been designed with an operation frequency of 352 MHz, up to 4 MeV acceleration, 10 mA beam intensity, and a continuous-wave (CW) operation mode to achieve 0.84 × 109 n/(s/cm2) of neutron production. However, the deuteron RFQ has been designed with an operation frequency of 200 MHz, up to 2.5 MeV acceleration, 15 mA of beam intensity, and a CW operation mode to achieve 1.02 × 109 n/(s/cm2) of neutron production. In this paper, we describe the merit of the deuteron based neutron source by comparing two types of the RFQ accelerators for proton and deuteron beams including the common system of the ECR ion source and Be target in detail.

Status of high intensity proton injector for Facility for Antiproton and Ion Research.

The high intensity proton injector for the international accelerator Facility for Antiproton and Ion Research located at GSI-Darmstadt in Germany consists of a pulsed 2.45 GHz microwave ion source, a Low Energy Beam Transport (LEBT), and an electrostatic chopper matching the proton beam to the radio frequency quadrupole. The ion source is based on electron cyclotron resonance plasma production and it has to provide a proton beam at 95 keV energy and up to 100 mA current. The LEBT system with two short solenoids each including two magnetic steerers will transport the proton beam into the compact proton linac, accelerating it to the energy of 68 MeV and serving as the injector of the upgraded heavy ion synchrotron (SIS18). This paper describes the commissioning of the proton injector including beam characterization measurements that have been done at CEA/Saclay in France and is currently at the final commissioning stage.

Low-energy beam transport system for MESA

An important part of the new accelerator MESA (Mainz Energy-recovering Superconducting Accelerator) is the low-energy beam transport system connecting the 100 keV electron source with the injector. The present setup includes the chopper and bunching system. The devices are of highest importance in order to achieve sufficient bunch compression, particularly at higher bunch charges and currents. With the circularly deflecting cavity of the chopper system it is possible to measure the longitudinal profile of the bunches upstream of the buncher, whereas downstream the longitudinal size will be measured by Smith-Purcell radiation. Based on experimental results obtained from this setup, we will discuss the beam parameters and compare them with simulations of the beamline.

Beam thermalization in a large gas catcher

Thermalization of fast ions in a buffer gas provides a method to transform the high-energy, exotic beams produced by projectile fragmentation at the National Superconducting Cyclotron Laboratory (NSCL) into low-energy beams. The process includes slowing down the fast exotic beams in solid degraders combined with momentum compression and removal of the remaining kinetic energy by collisions with a buffer gas. The original beam thermalization area for mass measurements at the NSCL was reconfigured to accommodate a new momentum compression beam line, a large radio-frequency (RF) gas catcher constructed by Argonne National Lab and a low-energy beam transport system. A large variety of exotic isotopes produced by projectile fragmentation and selected by the A1900 fragment separator was thermalized in the 1.2 m long gas catcher filled with helium at approximately 100 mbar. The ions were guided to an extraction nozzle with a combination of electrostatic and RF potentials and ejected by the gas flow. A novel RF ion guide was used in a differential pumping system to remove the helium and transport the ions into ultrahigh vacuum. Finally, the ions were accelerated to 30 kV for transport to various experiments. The distribution of the thermalized ions among chemical adducts is one of the operational challenges. The important steps implemented to minimize the production of the chemical adducts in the gas catcher are discussed. The operational status of the facility and some example results from characterization of the gas catcher operation with 37K and 47K beams are presented.

Development of 2.45 GHz ECR ion sources at IMP

The Ion Source Group at IMP has been undertaking a series of high intensity ion beam R&D projects. The first project is the development of the intense proton source and its low energy beam transport system (LEBT) for China Initiative Accelerator Driven Sub-Critical reactor (CiADS). The specific characteristics of the proton source are long-term reliability and flexible beam manipulation for the commissioning need of the Superconducting radio-frequency (SRF) accelerators. The LEBT is used to deliver 35 keV H+ beam to the entrance of a 2.1 MeV RFQ . And then the 2.1 MeV proton beam is further accelerated by the superconducting cavities to 25 MeV and eventually goes into a high power beam dumper. Another project is the development of the intense ion source for Jinping Underground Nuclear Astrophysics experiments (JUNA). The ion source was expected to provide 10 emA H+, 10 emA He+ or 2.5 emA He2+ beams for the study of (p, γ), (p, α), (α, p) and (α, γ) reactions in the first phase of the JUNA project. The main challenges of the ion source for JUNA project are production of intense He2+ beam, control of the beam contaminations and beam commissioning a wide beam energy range (70∼800 keV) . In this paper, the studies of these intense beam injector systems, for instance, beam intensities, species and ratio, beam transmission efficiency in the LEBT and also the beam optics matching to the downstream accelerator systems will be presented.

Record productions establish RF-driven sources as the standard for generating high-duty-factor, high-current H- beams for accelerators (Winner of the ICIS 2017 Brightness Award).

The Spallation Neutron Source operates reliably at 1.2 MW and will gradually ramp to 1.4 MW. This paper briefly recalls some of the struggles when the unprecedented project was started and ramped to 1 MW over a 3½ year period. This was challenging, especially for the H- ion source and the low-energy beam transport system, which make up the H- injector. It took several more years to push the H- injector to the 1.4 MW requirements, and even longer to reach close to 100% injector availability. An additional breakthrough was the carefully staged, successful extension of the H- source service cycle so that disruptive source changes became rare events. More than 7 A·h of extracted H- ions have been demonstrated with a single source without maintenance, more than twice the single-source quantity of ions produced by any other high-current H- accelerator facility. Achieving the 1.4 MW requirements with close to 100% availability and record-breaking source service cycles were the basis for the 2017 Brightness Award.

Start-to-end simulation with rare isotope beam for post accelerator of the RAON accelerator

The RAON accelerator of the Rare Isotope Science Project (RISP) has been developed to create and accelerate various kinds of stable heavy ion beams and rare isotope beams for a wide range of the science applications. In the RAON accelerator, the rare isotope beams generated by the Isotope Separation On-Line (ISOL) system will be transported through the post accelerator, namely, from the post Low Energy Beam Transport (LEBT) system and the post Radio Frequency Quadrupole (RFQ) to the superconducting linac (SCL3). The accelerated beams will be put to use in the low energy experimental hall or accelerated again by the superconducting linac (SCL2) in order to be used in the high energy experimental hall. In this paper, we will describe the results of the start-to-end simulations with the rare isotope beams generated by the ISOL system in the post accelerator of the RAON accelerator. In addition, the error analysis and correction at the superconducting linac SCL3 will be presented.

Design of an intense ion source and LEBT for Jinping Underground Nuclear Astrophysics experiments

The ongoing Jinping Underground Nuclear Astrophysics experiment (JUNA) will take the advantage of the ultralow background in China Jinping Underground Laboratory (CJPL), high current accelerator driven by on an ECR source and highly sensitive detector to study directly a number of important reactions for the first time within their relevant stellar energy range. A 2.45GHz ECR ion source is one of its key components to provide 10emA H+, 10emA He+ and 2.0emA He2+ beams for the study of (p,γ), (p,α), (α,p) and (α,γ) reactions in the first phase of the JUNA project. Ion beam is extracted from the source with energies up to 50kV/q. The following low energy beam transport (LEBT) system transports and matches the ion beam from the exit of ion source to the acceleration tube (AT). The design status of the ECR ion source and LEBT system for the JUNA project are presented. The potential risks of the ion source are also discussed and analysed.

Transport of intense proton beam in the presence of subdominant species in a low energy beam transport system

The dynamics of space-charge-dominated low energy proton beam in the presence of H2+ and H3+ beams has been studied in a solenoid based transport system using particle-in-cell (PIC) simulation method. Multispecies envelope equation and random search technique have been used to transport and match the primary beam considering two options. The PIC simulation shows the formation of hollow distribution of H2+ and H3+ beams around the proton beam in the first case where the waist of the proton beam is formed in between the solenoids and it is absent in the second case where the beam size is kept large in between the solenoids. Separation of hollow distribution appears more distinct as the proton fraction is increased and is almost independent of the combination of H2+ and H3+ beams for a given proton fraction. This effect helps to reject the unwanted species more effectively. The evolution of rms size and emittance of the proton beam has been studied in the presence of a circular aperture using KV and Gaussian distributions for the species in both the cases.

First results of 28 GHz superconducting electron cyclotron resonance ion source for KBSI accelerator.

The 28 GHz superconducting electron cyclotron resonance (ECR) ion source has been developed to produce a high current heavy ion for the linear accelerator at KBSI (Korea Basic Science Institute). The objective of this study is to generate fast neutrons with a proton target via a p(Li,n)Be reaction. The design and fabrication of the essential components of the ECR ion source, which include a superconducting magnet with a liquid helium re-condensed cryostat and a 10 kW high-power microwave, were completed. The waveguide components were connected with a plasma chamber including a gas supply system. The plasma chamber was inserted into the warm bore of the superconducting magnet. A high voltage system was also installed for the ion beam extraction. After the installation of the ECR ion source, we reported the results for ECR plasma ignition at ECRIS 2014 in Russia. Following plasma ignition, we successfully extracted multi-charged ions and obtained the first results in terms of ion beam spectra from various species. This was verified by a beam diagnostic system for a low energy beam transport system. In this article, we present the first results and report on the current status of the KBSI accelerator project.

A high intensity H2+ multicusp ion source for the isotope decay-at-rest experiment, IsoDAR

The Isotope Decay-At-Rest (IsoDAR) experimental program aims to decisively test the sterile neutrino hypothesis. In essence, it is a novel cyclotron based neutrino factory that will improve the frontiers in both high-intensity cyclotrons and electron flavor anti-neutrino sources. By using a source in which the usual H(-) ions are replaced with the more tightly bound H2(+) ions, we can negate the effects of Lorentz stripping in a cyclotron, reduce the overall perveance due to the space-charge effect, and deliver twice the number of protons per nuclei on target. To produce the H2(+), we are currently developing a dedicated multicusp ion source, MIST-1 (generation-1 Multicusp Ion Source Technologies at MIT), and a low-energy beam transport system for the IsoDAR cyclotron. This will increase the overall H2(+) current leading up to the cyclotron and improve the emittance of the beam injected into the cyclotron.

Simulation study of LEBT for transversely coupled beam from an ECR ion source.

A Low-Energy intense-highly charged ion Accelerator Facility (LEAF) program has been launched at Institute of Modern Physics. This accelerator facility consists of a superconducting Electron Cyclotron Resonance (ECR) ion source, a Low Energy Beam Transport (LEBT) system, and a Radio Frequency Quadrupole (RFQ). It is especially of interest for the extracted ion beam from the ECR ion source, which is transversely coupled, and this property will significantly affect the beam transmission in the LEBT line and the matching with the downstream RFQ. In the beam transport design of LEAF, beam decoupling in the LEBT is considered to lower down the projection emittances and the feasibility of the design has been verified by beam simulation with a transversely coupled beam from the ECR ion source.

Status of intense permanent magnet proton source for China-accelerator driven sub-critical system Linac.

Two compact intense 2.45 GHz permanent magnet proton sources and their corresponding low energy beam transport (LEBT) system were developed successfully for China accelerator driven sub-critical system in 2014. Both the proton sources operate at 35 kV potential. The beams extracted from the ion source are transported by the LEBT, which is composed of two identical solenoids, to the 2.1 MeV Radio-Frequency Quadrupole (RFQ). In order to ensure the safety of the superconducting cavities during commissioning, an electrostatic-chopper has been designed and installed in the LEBT line that can chop the continuous wave beam into a pulsed one. The minimum width of the pulse is less than 10 μs and the fall/rise time of the chopper is about 20 ns. The performance of the proton source and the LEBT, such as beam current, beam profile, emittance and the impact to RFQ injection will be presented.

Designing a test facility LEBT for RISP

Raon, the rare isotope accelerator of the Rare Isotope Science Project (RISP) in Daejeon, South Korea, is being designed to accelerate multiple-charge-state beams simultaneously. Using an Electron Cyclotron Resonance (ECR) Ion Source to produce the ions, Raon will transport the beam through two 90-degree bending magnets and a Low Energy Beam Transport (LEBT) system to a Radio Frequency Quadrupole (RFQ). A test facility is under development to test the components of the injector and LEBT system. A new LEBT, based upon the LEBT of the main driver linac, is being designed to fit within the test facility’s restrictive space requirements. This work will briefly review the main driver linac LEBT design, and then discuss the current status of the test facility LEBT design.

The IsoDAR high intensity H2+ transport and injection tests

This technical report reviews the tests performed at the Best Cyclotron Systems, Inc. facility in regards to developing a cost effective ion source, beam line transport system, and acceleration system capable of high H2+ current output for the IsoDAR (Isotope Decay At Rest) experiment. We begin by outlining the requirements for the IsoDAR experiment then provide overviews of the Versatile Ion Source (VIS), Low Energy Beam Transport (LEBT) system, spiral inflector, and cyclotron. The experimental measurements are then discussed and the results are compared with a thorough set of simulation studies. Of particular importance we note that the VIS proved to be a reliable ion source capable of generating a large amount of H2+ current. The results suggest that with further upgrades, the VIS could potentially be a suitable candidate for IsoDAR. The conclusion outlines the key results from our tests and introduces the forthcoming work this technical report has motivated.