Low Energy Beam Transport Research Articles

Lebt of the Heavy Ion Linear Accelerator

At the NRC “Kurchatov Institute” (Kurchatov Complex for Theoretical and Experimental Physics), the pulsed linear resonant heavy ion accelerator is being developed. The Low Energy Beam Transport (LEBT) channel transports the beam from a laser-plasma source of multi-charged ions with an A/Z ratio from 4 to 8 (up to Bi27+) to the RFQ. This paper shares the results of the beam dynamics simulation of the LEBT, which ensures the separation of the working fraction of the ion beam and its matching with the RFQ.

Characterization of the LEBT based neutron source

Neutron generation by implantation and subsequent beam interaction of 40 keV deuterons at Soreq Applied Research Accelerator Facility (SARAF) low energy beam transport (LEBT) section was measured and characterized. The generation of 2.45 MeV neutrons by a deuteron beam of several mA was verified by a neutron spectrometer. Relative neutron yields were studied as a function of beam energy and beam spot size using two types of available implantation surfaces. The buildup of neutron yield was studied at long and short time scales. Absolute neutron yield was measured via activation at several conditions. The maximum neutron yield that could be obtained at the SARAF LEBT is of the order of 107 n/s, which presents a convenient source for testing neutron instrumentation in DC or pulsed mode.

Phase space reconstruction technique for beam optimization in the Low Energy High Intensity Proton Accelerator (LEHIPA)

The Low Energy High Intensity Proton Accelerator (LEHIPA) has been commissioned to the design energy of 20 MeV at BARC, India. The low energy beam transport (LEBT) channel of LEHIPA consists of two solenoids and drift spaces for matching the 50 keV proton beam from the ECR ion source (ECR-IS) to the RFQ. The ion beam extracted from the ECR-IS also contains molecular species like H2 + and H3 +. Proton fraction in the beam is found to degrade slowly with time due to surface contamination of the plasma chamber and this reduction in proton beam current has implications for longitudinal and transverse beam dynamics. Hence, it becomes important to characterise the beam at different proton fraction levels to understand the end-to-end beam dynamics of LEHIPA. Computed Tomography (CT) technique has been used for the beam phase-space reconstruction in LEHIPA, using a Python program, incorporating the feature of filtering secondary species from the beam profiles measured using slit scanners in the LEBT. Simultaneous Algebraic Reconstruction Technique (SART) is used in the reconstruction since it is identified to be a better technique for a limited number of projections. The reconstruction program is benchmarked with the TraceWin beam dynamics code and implemented on the measured beam profiles to recreate the phase space distribution at the beginning of LEBT. Further, the tomographic reconstruction method is compared with the solenoid scan method and the rms emittance values are found to be in good agreement. The measured tomographic phase space distribution has then been used as TraceWin input for LEHIPA end-end beam dynamics simulations and the LEHIPA beam line parameters are re-optimized for minimum beam emittance growth. This paper presents the simulations of CT technique, benchmarking simulations with TraceWin, phase space reconstruction with measured beam profiles and beam dynamics studies of LEHIPA using the reconstructed beam distributions.

Operational Status and Future Plan of Proton Linear Accelerator at KOMAC

Since the second half of 2013, Korea Multi-purpose Accelerator Complex (KOMAC) has been supporting user beam service by using a 100-MeV proton linac and several beam line facilities. Proton beam service fields include various applications and research programs, such as material science, bio-medical science, semiconductor applications as well as nuclear physics and basic science. The 100-MeV linac is composed of an injector based on a 50-keV microwave ion source and two-solenoid LEBT (low energy beam transport), a 3-MeV RFQ with four-vane structure and conventional drift tube linac (DTL), where proton beam is accelerated from 3 MeV to 100 MeV. As the operation period of the proton accelerator exceeds 10 years and the cumulative operating time surpasses 30,000 hours, we judge that it is an opportune time to establish a long-term plan to prepare for the aging of the accelerator. To replace the currently operating RFQ, which shows degradation in performance (especially the beam transmission), we design a new RFQ with some modifications. For DTL, we are supposed to change the quadrupole magnet inside each drift tube from electromagnet type to permanent magnet type because the electromagnet has shown some trouble in view of long term stability. To leap forward in device and utilization technologies, we complete the construction of new facility of a Beam Test Stand (BTS) with a structure similar to the beam injection system (ion source, LEBT, RFQ) of the 100 MeV linear accelerator. We plan to actively conduct beam physics and accelerator research using this facility. Moreover, we are supposed to upgrade the proton linac to 1 GeV for spallation neutron source applications, which will be a long-term plan. In short term, we take phased approach with focusing the first phase at 200 MeV energy upgrade.

Design improvements to the SNS ion source and diagnostics

The U.S. Spallation Neutron Source (SNS) is a state-of-the-art neutron scattering facility delivering the world’s most intense pulsed-neutron beams to a wide array of instruments which are used to conduct investigations in many fields of science and engineering. The accelerator system is fed by an RF-driven, multicusp, H− ion source which nominally provides pulsed beam currents of 50-60 mA (1ms, 60Hz). This report provides a discussion of ongoing design improvements to the SNS ion source and Low Energy Beam Transport (LEBT) as well as diagnostic upgrades undertaken since the previous ICIS conference. These improvements include (i) simple mechanical modifications to the source outlet aperture which resulted in dramatically increased extracted beam current and comparable or lower emittance at similar beam currents, (ii) design improvements to the LEBT chopper target which will enable full power beam-dumping during physics studies, (iii) refinement of the SNS Allison emittance scanner that has enabled the first reliable LEBT beam measurements at full beam power (65kV, 50-100mA, 1ms, 60Hz) on the SNS ion source test stand and (iv) the implementation of a thermal imaging camera for the monitoring the LEBT electrode temperatures. (v) The design of an advanced Cs system, capable of more efficient Cs utilization with significantly lower Cs losses from the source is also presented. Mechanical details, computational simulations and experimental results are discussed within the context of these improvements.

Design and beam dynamics simulation of an 8 MeV compact accelerator-driven neutron source

A compact accelerator-driven neutron source is proposed at Sino-French Institute of Nuclear Engineering and Technology, Sun Yat-Sen University, called Sun Yat-Sen University Proton Accelerator Facility (SYSU-PAFA). The proton accelerator is composed of a proton electron cyclotron resonance source, a four-vane radio frequency quadrupole (RFQ), and an alternative phase focusing drift tube linac (APF-DTL). It can accelerate 10 mA proton beam to 8 MeV. Due to the high current, beam matching is particularly important. In order to achieve beam matching between various components, beam transport sections are needed. The beam transport line is divided into three segments. The Low Energy Beam Transport (LEBT) ensures that the beam parameters are matched before entering the RFQ. The Medium Energy Beam Transport (MEBT) segment efficiently transfers the beam between the RFQ and DTL. The High Energy Beam Transport (HEBT) focuses on transporting the beam to the targets. The design goal of beam transport line is as short as possible while ensuring high efficiency of beam transportation. SYSU-PAFA has an overall transmission efficiency of 99%, with optimal transverse matching conditions between beam transport and RFQ or DTL accelerators. The efficient use of solenoids and magnets allows for a compact transmission section, resulting in a total length of 13.6 meters, shorter than most accelerators at the same beam energy. This paper will provide the detailed beam dynamics of the compact accelerator.

Permanent magnet ECR ion source and LEBT dipole for single-ended heavy ion ToF-ERDA facility

We present the status of the ion source and low energy beam transport prototyping for a single-ended heavy ion time-of-flight elastic recoil detection analysis equipment. The environmentally friendly concept is based on a permanent magnet ECR ion source and dipole magnet on a 500 kV platform without SF6 insulation, producing high charge state noble gas ion beams, e.g. 3–6 MeV argon. The ion fluxes of Ar6+–Ar12+ achieved with the CUBE-ECRIS permanent magnet minimum-B quadrupole ion source exceed 1-10 particle nA required for the low energy ToF-ERDA application. The CUBE-ECRIS can produce over 1 particle nA krypton and xenon beams up to charge states Kr19+ and Xe24+, which enables extending the scope of the ToF-ERDA application. The integration of an adjustable-field permanent magnet dipole into the CUBE-ECRIS test stand at the JYFL accelerator laboratory is described briefly.

Recent advancements with the H− injector performance for the Spallation Neutron Source operation and upgrade

The Spallation Neutron Source (SNS) located at the Oak Ridge National Laboratory is an accelerator-based, pulsed neutron facility utilized for a broad range of scientific research and industrial applications. In the past 5 years, the facility has reliably been operated at its baseline design beam power of 1.4 MW, and it is currently undertaking an upgrade to double its power to 2.8 MW. A 65-keV H− injector, which comprises an rf-driven H− ion source and an electrostatic low energy beam transport, delivers the required high-current, time-structured H− beam to the accelerator. The H− injector can reliably provide 50-60 mA beam current at 6% duty-factor (1 ms, 60 Hz) for a 3-4 month service cycle. To ensure sufficient operational margins for the SNS routine operations and ongoing upgrade requirements, the injector system has been continuously improved on a R&D test stand. This paper presents the operational status and recent advancements with the injector system performance including the enhanced ion source beam output capability up to ∼110 mA, the improved ion source plasma ignition reliability using a 27.12-MHz RF system, and the upgraded LEBT beam chopper system etc.

Space-Charge Effects on Transverse Emittance in the Extraction Region of the RIKEN 28-GHz ECRIS

To confirm the significance of space-charge effects (SCEs) on the emittance growth in the “extraction region” of the RIKEN 28-GHz electron-cyclotron-resonance ion source (ECRIS), we reconstructed the phase-space distribution of argon (Ar) beams traveling through high-intensity nitrogen (N) beams and reaching at the end of “extraction region”. Here, the “extraction region” is defined as the low-energy beam transport region between the ECRIS puller electrode and a magnetic analyzer. The transverse phase-space distribution (PSD) of the Ar beams, which were exposed to the SCEs due to the high-intensity N beams, was measured after magnetic analysis using the pepper-pot emittance meter (PPEM). Because we suppressed each Ar beam current below 50 µA, the expansion in the transverse phase-space distribution due to the SCEs after the magnetic analyzer could be sufficiently reduced. Sufficient angular resolution was achieved by improving the image analysis of PPEM measurements with the “optical flow method”. Therefore, we obtained a transverse PSD at the endpoint of the extraction region of the ECRIS using the three dimensional backtracking. The obtained rms emittance of the Ar10,11,13+ were found to increas as a function of the extraction current I ext, while those of Ar16+ were found to be nearly constant. The reconstructed PSD at the end of the “extraction region” shows that the smaller the M/Q, in other words, the larger the charge state Q, the smaller both the positional and angular distribution for each I ext. To reveal the space charge effect on the beam trajectory passing though the “extraction region”, further experimental measurements and analyses are underway, including detailed trajectory simulation.

Low-energy ion beam diagnostics: an integrated solution

High gradient accelerator injectors have been widely studied throughout the world-leading accelerator facilities. The demand for high frequency cavities has led the Detector, Accelerator and instrumentation laboratory (KAHVELab) in Istanbul to deploy a four-vane Radio Frequency Quadrupole (RFQ) operating at 800 MHz to accelerate 20 keV protons to 2 MeV. The protons from the microwave discharge ion source are transversely matched to the RFQ via an optimized Low Energy Beam Transport (LEBT) line which also contains an integrated measurement station, called measurement station (MBOX). The MBOX is used to measure the proton beam's current along with pulse length duration, profile as well as the beam emittance upstream of the RFQ. It contains a number of home-built diagnostic tools: a Faraday cup, a scintillator screen and a pepper pot plate (PP). The analysis software is also locally developed and tested for the PP photo analysis. In this note, the design, construction and tests of the integrated measurement station are discussed. The results from various measurements, especially on beam profile and charge, are compared to the simulation predictions.

An integrated tool for ion linac design

The initial design phase of an ion linac's front end often requires the use of several software programs, each dedicated to a specific component. These components typically include the ion source, a low-energy beam transmission line (LEBT) equipped with electromagnets, a measurement station, and finally the Radio Frequency Quadrupole (RFQ). Unfortunately, many of the legacy and proven software tools in this field lack user-friendly GUIs and have significant learning curves. In this paper, we present a novel approach: a unified software solution that offers a cohesive GUI and integrates with existing legacy software. This single-software approach not only simplifies the design process but also significantly reduces the time required for design and optimization. Our method has been successfully applied to various design configurations, demonstrating its efficiency in both the learning and design phases, compared to the traditional multi-software approach. In addition, we present DemirciPRO as an illustrative implementation of our unified software approach. This software tool showcases real-world scenarios and comparisons drawn from an ongoing proton linac project. DemirciPRO offers a cohesive user interface for designing an ion source, a Low-Energy Beam Transport (LEBT) line, and, ultimately, a Radio-Frequency Quadrupole (RFQ). Each module is capable of utilizing the output from the preceding one along the beamline. Furthermore, it possesses the capability to trace the trajectories of beam particles through the LEBT line using relevant transport matrices and through the RFQ using the leap-frog method.

Overview of neutral beam injectors for plasma heating and diagnostics developed at Budker INP

An overview of the neutral beam injectors developed at the Budker Institute of Nuclear Physics in Novosibirsk during the last 10 years is presented. These neutral injectors are used for plasma diagnostics, heating and current drive in modern fusion devices with magnetic confinement. An arc or a radio-frequency (RF) discharge generates a plasma in the ion sources of the injectors, and a positive hydrogen or deuterium ion beam is extracted and accelerated by a multiaperture ion-optical system (IOS). The accelerated ion beam is converted into a neutral one in a gas target. The precision multiaperture IOS with spherically concave electrodes provides ballistic focusing of the neutral beam. The high-energy, high-power beam injector based on negative ions, which is currently under development, is described as well. It comprises a RF negative ion source and a wide-aperture electrostatic accelerator separated from the source by a low-energy beam transport line, thereby improving the injector reliability.

Design of the gradient dipole magnet for LLICTF

The Lanzhou Light Ion Cancer Therapy Facility (LLICTF) is a compact medical accelerator currently under construction. It is designed to treat cancer using a 230 MeV, 30 mA H+ beam and a 85 MeV/u, 1 mA 3He2+ beam. The facility comprises two ion sources, a low-energy beam-transport (LEBT), a Radio Frequency Quadrupole (RFQ), a medium-energy beam-transport (MEBT), and the main ring accelerating structure. Due to the presence of two ion sources, it is necessary to introduce a dipole magnet which is symmetrically focused as much as possible to meet the focusing requirements of the LEBT beam. Therefore, a gradient dipole magnet has been designed to achieve this symmetrical focusing. This paper discusses the theoretical and simulated symmetric focusing of the gradient dipole magnet. It also analyzes the effect of fringe fields and space charge. Additionally, this paper presents the results of the model design with CST and the multi-particle simulation results with TraceWin.

Design and experiments of a compact electrostatic low energy beam transport with a double Einzel-lens for a transportable neutron source.

A transportable, compact, accelerator-based neutron source is under development at Xian Jiaotong University. An electrostatic low energy beam transport (LEBT) structure with a double Einzel-lens setup was adopted due to its short length and low power consumption. It can transport a pulsed proton beam to the radio frequency quadrupole with a required beam current of 15 mA and an energy of 30keV. We performed detailed structure optimization and beam tracking to achieve beam matching and small emittance growth. In addition, the fast chopper, beam steering, and diagnostic devices are integrated into the LEBT. The fabrication and assembly of the proton injector have been completed, and beam commissioning was carried out to measure the beam current and Twiss parameters. The design strategy, beam simulation, and experimental results are presented and discussed in this paper.

Beam commissioning of the SARAF Injector and MEBT (protons)

The SARAF Phase II cryogenic linear accelerator (linac) is currently under construction and will be commissioned through collaborative efforts between SNRC and CEA. The linac will accelerate a 5 mA pulsed/continuous wave (CW) proton and deuteron beam, reaching energies of up to 35 MeV and 40 MeV, respectively. The linac injector consists of Phase I components, including an ECR ion source, a Low-Energy Beam Transport (LEBT) line, and a 4-rod Radio Frequency Quadruple (RFQ). Additionally, a new Medium Energy Beam Transport (MEBT) line has been installed and integrated into the injector infrastructure. The MEBT includes three rebuncher resonators, magneto-optical elements, and beam diagnostics. The MEBT beam diagnostics, as well as the Phase I D-plate installed downstream, were used for beam characterization. The downstream-installed Temporary Beam Line (TBL) and a prototype of the Gallium Indium Liquid Target (GALIT) were used for commissioning, operating at high beam duty cycles, including CW mode. The report describes the proton beam commissioning process of the injector prior to the delivery of the cryomodules, scheduled for the second half of 2023.

Development of Allison scanner to measure transverse emittance at low energy beam transport of rare-isotope accelerator complex for ON-line experiments

The Rare-isotope Accelerator complex for ON-line experiments is a heavy-ion accelerator facility that accelerates a stable or rare isotope beam up to 400 kW with an energy of 200 MeV/u. Various heavy-ion beams are generated from the Electron Cyclotron Resonance Ion Source, with an energy of 10 keV/u and separated according to A/Q at the first dipole magnet (DM). To measure beam transverse emittance at the Low Energy Beam Transport section, two Allison scanners are installed behind the DM for the X and Y directions. It consist of a servo motor for driving, a Faraday cup for current measurement, deflection plates, and electronic device. The measurable range of beam angle in of the Allison scanner is determined by the structure of the deflection plate and designed based on mathematical calculations. Experimental Physics and Industrial Control System (EPICS) is adopted to integrate and control a variety of devices. To control the complex measurement sequence of the Allison scanner, an EPICS sequencer module was used. Normalized emittance is calculated by python code with Pyepics module using phase space distribution data. In this paper, we present the detailed design of the Allison scanner, the configuration of the control system, and the experimental results using an Ar9+ 30 μA beam.

Deep neural network-based prediction for low-energy beam transport tuning

Deep neural network-based prediction for low-energy beam transport tuning

Improvement of multi-harmonic buncher’s quality factor for RAON

The high-intensity rare-isotope accelerator RAON, a component of the Rare Isotope Science Project, was developed to accelerate heavy ions from elements ranging from proton to uranium. The injector line consists of an Electron Cyclotron Resonance Ion Source, a Low Energy Beam Transport line, a Radio Frequency Quadrupole (RFQ), and a Medium Energy Beam Transport line. To improve beam quality, a multi-harmonic buncher (MHB) was proposed for inclusion before the RFQ. The MHB is needed to efficiently utilize two beams with different mass-to-charge (A/q) ratios. The fundamental frequency of the MHB is half the frequency of the RFQ; as such, a harmonic synthesis is effectively bunching a beam. Electric field simulations of the MHB were conducted using the CST Microwave Studio (MWS). The electrodes were designed as cone- type electrodes so that the electric field can be concentrated between the electrodes through which the beam passes. The electric field was optimized to account for structural changes such as gap length between electrodes, resonator position and other design details. The model optimized in the simulation tool was engineered through the 3D Inventor program.

Commissioning results of single bunch selection system for the RAON heavy-ion accelerator facility

To enable neutron time-of-flight experiments at the RAON heavy-ion accelerator facility, we tested a single bunch beam selection method by combining an RF chopper and a double gap buncher in the low-energy beam transport section. The RF chopper converts a CW beam into a hundreds-nanosecond pulsed beam. Then, the double gap buncher performs bunching to shorten the pulse length to less than one radio frequency quadrupole (RFQ) cycle. Ideally, a single isolated bunch can be achieved after the RFQ. In this study, we discuss the design concept of the single bunch selection system and present initial beam commissioning results.

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.