Low Energy Beam Transport Line Research Articles

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.

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.

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.

Transverse emittance measurement in 2D and 4D performed on a Low Energy Beam Transport line: benchmarking and data analysis

2D and 4D transverse phase-space of a low-energy ion-beam is measured with two of the most common emittance scanners. The article covers the description of the installation, the setup, the settings, the experiment and the benchmark of the two emittance meters. We compare the results from three series of measurements and present the advantages and drawbacks of the two systems. Coupling between phase-space planes, correlations and mitigation of deleterious effects are discussed. The influence of background noise and aberrations of trace-space figures on emittance measurements and RMS calculations is highlighted, especially for low density beams and halos. A new data analysis method using noise reduction, filtering, and reconstruction of the emittance figure is described. Finally, some basic concepts of phase-space theory and application to beam transport are recalled.

Ion source and LEBT of KAHVELab proton beamline

The KAHVE Laboratory, at Boğaziçi University, Istanbul, Turkey is home to an educational proton linac project. The proton beam will originate from a 20 keV H+ source and will be delivered to a two module Radio Frequency Quadrupole (RFQ) operating at 800 MHz via a low energy beam transport (LEBT) line. Currently, the design phase being over, commissioning and stability tests are ongoing for the proton beamline which is already produced and installed except the RFQ which is being manufactured. This work summarizes the design, production and test phases of the ion source and LEBT line components.

Commissioning of the 7 MeV H[formula omitted] linac injector for a 200 MeV proton synchrotron

This paper describes the beam commissioning progress of the 7 MeV H− linac injector for the proton synchrotron of Xi’an 200 MeV Proton Application Facility (XiPAF). To fulfill a flux of 105∼108p/cm2/s with a uniformity better than 90% on a 3 cm × 3 cm sample size at the experimental station, the number of the accumulated protons in each cycle in the synchrotron is designed to be larger than 2 × 1011. The protons are acquired from the H− beam stripped by the carbon foil, which enables transverse space painting during injection. The maximum pulse length of the injected beam is 40μs. With an estimation of 40 for the intensity gain factor, the injected beam is required to have a peak current of higher than 1 mA, with the normalized transverse emittance of 90% particles less than 6 and 4 πmm mrad for the horizontal and vertical planes, respectively, and the momentum spread of 90% particles within ±0.45%. The injector mainly consists of an H− ion source, a low energy beam transport line (LEBT), a 3 MeV radio frequency quadrupole (RFQ) accelerator, a 7 MeV interdigital H-mode drift tube linac (IH-DTL), and an injection beam transport line. After several stages of beam commissioning, the linac injector has reached a pulsed peak current of 2.5 mA, with normalized emittance (90% particles) less than 4.4 and 2.2 πmm mrad, 90% momentum spread less than ±0.55%, which lays a good foundation for the beam commissioning of the synchrotron.

Beam based diagnostic and four dimensional transverse emittance measurement using solenoid scan for 100 keV thermionic electron gun at VECC, Kolkata

Solenoid in the low energy beam transport line used for focusing 100 keV electron beam has also been utilized as a beam diagnostic tool. 4D transverse emittance has been determined by analyzing the second moment beam distribution on a view screen placed downstream using solenoid scan technique which require no a-priori assumptions of the input beam. The measured transverse emittance is compared with the emittance tomographically reconstructed from the measured beam profiles corresponding to the same set of solenoidal fields in the solenoid scan.

Optimization of transverse emittance for RF-driven negative hydrogen ion source developed at China Spallation Neutron Source.

The China Spallation Neutron Source project Phase-II aims to deliver 500 kW beam power to the spallation target. To meet the beam power requirement, an RF-driven negative hydrogen ion source with an external-antenna has been developed. In order to optimize the beam transmission through the radio frequency quadrupole and the downstream linac, the low energy beam transport line needs to be carefully studied and the transverse emittance is focused in this paper. With computational simulation and experimental verification, the emittance growth caused by nonlinear magnetic fields of the solenoid and the residual magnetic fields at the measuring position has been carefully analyzed. The measurement uncertainty of the double-slit scanner has also been quantitatively estimated. Using the same plasma-beam boundary setting, the beam extraction system is also optimized with particle tracking simulation in CST PARTICLE STUDIO.

Beam dynamics simulation study for longitudinal bunch length measurement of RF modulated thermionic electron gun at VECC, Kolkata

A superconducting electron linac (e-linac) photo-fission driver is under construction at VECC for the upcoming rare isotope beam facility called ANURIB. Electron gun and straight low energy beam transport (LEBT) line has been installed and is operational at a test area, delivering electron beam of 100 keV. We discuss beam dynamics and analytical calculations leading to optimal parameters of analysing section of LEBT line and RF deflector cavity that will be used for measuring longitudinal characteristics for the low energy electron beam.

Production and transport of H2 + into the IMISC superconducting cyclotron

In the current study, the design of the ion beam required by the IMSIC, from the ion source to the beam transport line are reported. IMSIC is a four-spiral-sector cyclotron designed to accelerate protons in the form of H2 + particles up to 250 MeV. The required H2 + particles source was designed in the form of Electron Cyclotron Resonance Ion Source (ECRIS) externally feeding the cyclotron through a Low Energy Beam Transport (LEBT) line. For ECRIS, both plasma confining and extractor systems were modeled conceptually and optimized to produce the required particle beam. The extracted beam was coupled with the LEBT line. To model the LEBT line two set of forces were considered: (i) forces originating from the external fields and (ii) space-charge forces originating from the beam internal fields. The LEBT line was designed to separate the desired ions from the undesired contaminations as well as to modify the desired beam before feeding to the cyclotron.

Power control of CiADS core with the intensity of the proton beam

This paper reports the control method for the core power of the China initiative Accelerator Driven System (CiADS) facility. In the CiADS facility, an intense external neutron source provided by a proton accelerator coupled to a spallation target is used to drive a sub-critical reactor. Without any control rod inside the sub-critical reactor, the core power is controlled by adjusting the proton beam intensity. In order to continuously change the beam intensity, an adjustable aperture is considered to be used at the Low Energy Beam Transport (LEBT) line of the accelerator. The aperture size is adjusted based on the Proportional Integral Derivative (PID) controllers, by comparing either the setting beam intensity or the setting core power with the measured value. To evaluate the proposed control method, a CiADS core model is built based on the point reactor kinetics model with six delayed neutron groups. The simulations based on the CiADS core model have indicated that the core power can be controlled stably by adjusting the aperture size. The response time in the adjustment of the core power depends mainly on the adjustment time of the beam intensity.

ENGINEERING OF THE LOW-ENERGY BEAM TRANSPORT LINE IN THE Не⁺ IONS LINAC

The design of a low-energy beam transport line in the helium ions linear accelerator is proposed. For experiments with the low-energy helium ions the vacuum chamber in a transport line is in addition included for an irradiation of investigated materials. The mathematical modeling method investigates coordination variants of an injector beam output emittance with an accelerating structure acceptance with use of electromagnetic quadrupole lenses, electrostatic lenses and the focusing solenoid. It is shown that the optimal variant, ad hoc, is the focusing solenoid application. The calculated value of a current of the helium accelerated ions makes 4.5 mА.

Design study of multi-charge low energy beams transport for BISOL post accelerator

Beijing Isotope-Separation-On-Line Neutron-Rich Beam Facility (BISOL) post accelerator is designed to accelerate RIBs extracted from Isotope Separation On-Line (ISOL) ion source and the beam energy will be upto 150 MeV/u for Stannum. The accelerated RIBs will be served as projectile to produce isotopes far from stable line. Multi-charge state beams transport is adopted to increase beam current, a low energy beam transport (LEBT) line is desired for selecting charge states, bunching beam from continuous wave (CW) ISOL beams and match the beam into a CW 81.25 MHz radio frequency quadrupole (RFQ). This paper mainly presents the design study of BISOL multi-charge LEBT line. The detailed optics design and beam dynamics simulation are presented. Due to lower beam energy (3 keV/u) and higher transverse emittance (0.2n,rπmmmrad), the longitudinal nonlinear effect in the bunching system cannot be ignored compared to existing LEBT bunching systems, we have investigated two novel bunching and injection modes (180∘@20.3125 MHz, 270∘@20.3125 MHz) as well as the traditional mode (180∘@40.625 MHz) to optimize the output longitudinal emittance. The beam dynamics analysis indicates that the output longitudinal rms emittance can be lowered by nearly 33% with the bunching mode of 270∘@20.3125 MHz compared to traditional mode. The detailed results are presented in this paper.

一种用于C-ADS 低能束流传输线束流强度控制的新型可调限束光阑

A novel adjustable aperture is developed for the low energy beam transport line (LEBT) of the China Accelerator Driven Subcritical System (C-ADS). Two relatively rotating mirror-symmetry cores are adopted for the adjustable aperture to scrape unwanted outer particles, improve the beam quality and reduce the beam losses, and most of all, realize continuously tunable beam current and meet the requirement of round beam. The results of simulation and test show that the unwanted outer particles can be cut away and the beam current can be adjusted continuously online within the range of 0 to 10 mA. This device provides a convenient beam tuning method for the proton linear accelerator, which can satisfy the stable and reliable online operation of C-ADS linear accelerator.

Development and testing of radio frequency modulated electron Gun at VECC, Kolkata

A superconducting electron linac (e-Linac) photo-fission driver is under construction at VECC for the upcoming rare isotope beam facility called ANURIB. The first stage consists of an injector linac based on 1.3 GHz superconducting radio frequency technology designed for accelerating 10 MeV, 2 mA CW electron beam. An rf modulated thermionic electron gun (E-Gun) has been developed and tested for this injector linac. The E-Gun will allow continuous beam operation up to 300 keV with around 3 pC charge per pulse at 650 MHz. Electron beam with RF modulation is extracted from the gun and intensity, energy, size of the DC beam as well as trans-conductance of the electron source are measured. The design of some major components for the electron gun and low energy beam transport line is discussed and results of beam tests are presented.

Deuteron beam commissioning of the linear IFMIF prototype accelerator ion source and low energy beam transport

During the EVEDA (engineering validation and engineering design activities) phase of the International Fusion Materials Irradiation Facility (IFMIF) project, a 125 mA/9 MeV linear prototype accelerator (LIPAc) has to be built, tested and operated in Rokkasho-mura (Japan). Involved in this project for several years, CEA-Saclay designed the injector of this accelerator which is composed of an electron cyclotron resonance ion source, delivering a 140 mA deuteron beam at 100 keV, and a low energy beam transport (LEBT) line to match the beam for the injection into the radio-frequency quadrupole. In this paper, the components of the LIPAc injector are described.The commissioning of the ion source and LEBT with beam started in November 2014. The different phases of the commissioning are explained and some noticeable experimental results obtained with a beam at 100 keV are presented.

FPGA-based interlock system for the chopper of the Linear IFMIF prototype accelerator injector

The Linear IFMIF (International Fusion Materials Irradiation Facility) Prototype Accelerator (LIPAc) injector consists of a 140 mA proton/deuteron source, its associated low energy beam transport line (LEBT) as well as ancillaries such as water cooling skid, vacuum groups, High Voltage Power Supplies (HVPS), etc. A specific element, the beam “Chopper”, was included in the LEBT to generate short (˜ 100μs) and sharp-edged beam pulses (˜10μs) and allow the use of interceptive diagnostics in the high energy part of the LIPAc during commissioning phases of the Radio Frequency Quadrupole RFQ (5 MeV) and the Superconducting Radio Frequency SRF Linac (9 MeV). The chopper was designed to operate in pulsed mode with very sharp rise and fall times, meaning the chopper will be used to “cut” the long rise time of the source as well as the fall time of the beam pulse.The chopper thermal screen has not been designed to withstand very high beam power (i.e., beam length and duty cycle need to be monitored); in addition, the chopper HVPS needs to be monitored in real time to detect a possible trip and extract the beam before downstream devices are damaged. For these applications, standard PLC based interlocks are too slow; therefore, faster solutions are envisaged.The proposed solution for the required interlock system is based on COTS technology with XILINX FPGAs using RIO (Reconfigurable Input/Output) technology from National Instruments (CompactRIO platform). The paper discusses the implementation of the interlock system, the response times of the proposed architecture and the fitness of the technology. Additionally, the system can be integrated into the IFMIF control system using EPICS as a standalone solution.

Radio frequency measurement and tuning of a 13 MeV Alvarez-type drift tube linac for a compact pulsed hadron source.

This paper describes the radio frequency (RF) measurement and tuning result of a 13 MeV Alvarez-type drift tube linac (DTL) for a compact pulsed hadron source (CPHS) at Tsinghua University. The design, machining, assembly, and alignment of the DTL are presented for integrity. The CPHS project consists of a high-current proton linac (13 MeV, 16 kW, peak current of 50 mA, 0.5 ms pulse width at 50 Hz), a neutron target station, a small-angle neutron scattering instrument, and a neutron imaging/radiology station. The linac contains an electron cyclotron resonance ion source, a low energy beam transport line, a four-vane radio frequency quadrupole (RFQ) accelerator, an Alvarez-type DTL, a high energy beam transport line, and a RF power supply and distributor. Construction on the CPHS started in June 2009, and the CPHS has provided 2000 h since 2013 to users with the neutrons produced by the 3 MeV proton beam from the radio frequency quadrupole bombarding on the beryllium target as an achievement of its mid-term objective. Presently, the tuning of the assembled DTL cavity has been completed successfully. The 4.3-m-long DTL consists of 40 accelerating cells, among which 39 full-length drift tubes (DTs) are suspended inside the cavity, and two half-length DTs are mounted inside the two end flanges of the cavity. Each DT contains a permanent magnet quadrupole. Thirteen post couplers and nine tuners are available for the tuning of the field. The relative error of the field after tuning is within ±1.6%, with a tilt sensitivity within ±33%/MHz in all cells. The beam energy will reach its designed value of 13 MeV after the DTL is installed in the beam line downstream the 3 MeV RFQ accelerator.