GeV Rapid Cycling Synchrotron Research Articles

J-PARC linac and RCS – operational status and upgrade plan to 2-MW

The linac and the 3 GeV rapid-cycling synchrotron (RCS) at the Japan Proton Accelerator Research Complex (J-PARC) were designed to provide 1-MW proton beams to the following facilities. Due to the improvement of the accelerator system, we accelerated a 1-MW beam with a small beam loss. The lack of anode current in the radiofrequency (RF) cavity, rather than beam loss, limits the RCS beam power. Recently, we developed a new acceleration cavity that can accelerate a beam with a low anode current. This new cavity enables us to reduce the requirement for the anode power supply and accelerate a beam of more than 1 MW. We considered how to achieve beam acceleration beyond 1 MW. So far, a beam of up to 1.5 MW is expected to be accelerated after replacing the RF cavity. We also studied to achieve an up to 2-MW beam in J-PARC RCS.

High Intensity Beam Operation of J-PARC RCS With Minimum Beam Loss

The 3-GeV RCS (Rapid Cycling Synchrotron) of J-PARC (Japan Proton Accelerator Research Complex) at present operates at a high intensity beam near to 1 MW beam power. The beam loss and the corresponding residual radiation are key issues for beam intensity ramp up. Based on detail numerical simulations and systematic beam studies the beam loss has been well mitigated to a minimum level. The residual beam loss at 1 MW beam power is mostly due to unavoidable foil scattering of the circulating beam during injection. We have identified almost all major beam loss sources and optimized to minimize the beam loss for achieving a stable operation at 800 kW beam power since April 2022.

Development of new synchronized data system for J-PARC RCS

In J-PARC 3 GeV Rapid Cycling Synchrotron, the synchronized data system with reflective memory was constructed. However, this system has been operated for more than 10 years, it is essential to take countermeasures against deterioration over time. In addition, this system is difficult to support the large data sizes that have been recently requested. Therefore, we proposed a new synchronized data generation method. The test bench for a new synchronized data system that implements the new method was configured and its performance was verified. This result leads to the development of a new synchronous data system based on data transfer via LAN. In this paper, we describe the outline of the new synchronized data generation method and the results of performance tests.

Demonstration of a kicker impedance reduction scheme with diode stack and resistors by operating the 3-GeV rapid cycling synchrotron of the Japan Proton Accelerator Research Complex

Demonstration of a kicker impedance reduction scheme with diode stack and resistors by operating the 3-GeV rapid cycling synchrotron of the Japan Proton Accelerator Research Complex

Recent results of beam loss mitigation and extremely low beam loss operation of J-PARC RCS

In the 3-GeV RCS (Rapid Cycling Synchrotron) at J-PARC (Japan Proton Accelerator Research Complex), multi-turn H− charge-exchange injection is performed by using a thin stripped foil. The residual radiation at the injection area caused by the uncontrolled beam loss occurred by foil scattering of the circulating beam is a serious issue for regular maintenance works. In addition, the beam loss at the collimator section and its downstream caused for a large emittance beam also should be reduced, especially at high intensity operation. For that purpose we have minimized injection beam size and implemented a smaller size stripper foil. The circulating beam hitting rate is reduced by using a smaller foil, while an optimized vertical angle of the smaller injection beam for vertical transverse painting also gave a reduction of the circulating beam emittances and resulted a further significant beam loss mitigation at the collimator section and its downstream. As a result, the residual radiation after user operation at 700 kW beam power was also measured to be significantly reduced.

Design studies on a high-power wide-band RF combiner for consolidation of the driver amplifier of the J-PARC RCS

A power upgrade of the existing 8-kW solid-state driver amplifier is required for the acceleration of high intensity proton beams on the J-PARC 3-GeV Rapid Cycling Synchrotron. The development of a 25-kW amplifier with gallium nitride (GaN) HEMTs, based on 6.4-kW modules is ongoing. The combiner is a key component to achieve such a high output power over the wide bandwidth required for multi-harmonic RF operation. This paper presents the preliminary design of the combiner. The circuit simulation setup and results, including the realistic magnetic core characteristics and frequency response of the cable, are reported.

Development of the novel and superior adaptive beam-loading compensation system calculated in the frequency domain for the J-PARC Linac

The Japan Proton Accelerator Research Complex (J-PARC) is one of the highest intensity proton accelerator facilities in the world. Its accelerator consists of a 400-MeV linac (LINAC), a 3-GeV rapid-cycling synchrotron (RCS), and a 30-GeV main ring (MR) and its beam is provided for wide-ranging applications. The peak current of the beam at LINAC had been increased from 30 mA to the design value of 50 mA in 2018. Therefore, the performance of the beam-loading compensation implementing in the low-level radio frequency (LLRF) system has been more important to satisfy the stability of the accelerating gradient. Although the iterative learning control (ILC) scheme with adaptive ability was demonstrated, the practical use of ILC was not convenient for large accelerators such as the J-PARC LINAC with forty-nine RF stations. Therefore, we developed at novel and superior adaptive beam-loading compensation system that was calculated in the frequency domain. Compared to the scheme of the previous ILC, the newly developed system is useful because it does not require parameter adjustment using the beam. In the experimental results utilizing this system, the optimum tables of FF_BEAM were able to be obtained as a smaller number of iterations. The peak-to-peak stability of amplitude was achieved to ± 0.23% and the peak-to-peak stability of phase was improved to ± 0.036°. In addition, errors such as white noise did not accumulate for the table of FF_BEAM and this system solved the problem of the divergence when the number of iterations was increased. This implementation of the adaptive beam-loading compensation system calculated in the frequency domain will potentially contribute to the improvement of the J-PARC LINAC LLRF, and this system may lead to a stable user operation. This system is so simple in principle and effective that it could be applied to other linear accelerators with the pulsed beam.

Design and actual performance of J-PARC 3 GeV rapid cycling synchrotron for high-intensity operation

ABSTRACT In the Japan Proton Accelerator Research Complex, the purpose of the 3 GeV rapid cycling synchrotron (RCS) is to accelerate a 1 MW, high-intensity proton beam. To achieve beam operation at a repetition rate of 25 Hz at high intensities, the RCS was elaborately designed. After starting the RCS operation, we carefully verified the validity of its design and made certain improvements to establish a reliable operation at higher power as possible. Consequently, we demonstrated beam operation at a high power, namely, 1 MW. We then summarized the design, actual performance, and improvements of the RCS to achieve a 1 MW beam.

Dependence of charge-exchange efficiency on cooling water temperature of a beam transport line

The 3-GeV Rapid Cycling Synchrotron at the Japan Proton Accelerator Research Complex supplies a high-intensity proton beam for neutron experiments and to the Main Ring synchrotron. Various parameters are monitored to achieve a stable operation, and it was found that the oscillations of the charge-exchange efficiency and cooling water temperature were synchronized. We evaluated the orbit fluctuations at the injection point using a beam current of the injection dump, which is proportional to the number of particles that miss the foil and fail in the charge exchange, and profile of the injection beam. The total width of the fluctuations was approximately 0.072 mm. This value is negligible from the user operation viewpoint as our existing beam position monitors cannot detect such a small signal deviation. This displacement corresponds to a 1.63 × 10− 5 variation in the dipole magnetic field. Conversely, the magnetic field variation in the L3BT dipole magnet, which was estimated by the temperature change directly, is 4.08 × 10− 5. This result suggested that the change in the cooling water temperature is one of the major causes of the efficiency fluctuation.

The machine protection system for CSNS

BackgroundThe China Spallation Neutron Source (CSNS) accelerator consists of an 80 MeV H- LINAC, a 1.6 GeV rapid cycling synchrotron (RCS) and two beam transport lines. The uncontrolled beam may permanently damage the components or lead to very high residual radiation dose along the beam line. So the equipment protection must be deliberately designed and implemented.PurposeThe machine protection system (MPS) protects components from being damaged by the beam. The response time requirement for the CSNS MPS is less than 20 ms, so the PLC (programmable logic controller) was adopted to implement the interlock logic.MethodsThe MPS was implemented as a two-tier architecture system, and developed through utilizing PLC and Experimental Physics and Industrial Control System (EPICS) software toolkits. The application logic was taken into careful consideration during the implementation stage. An embedded CPU module can function as an IOC accessing PLC I/O modules through the sequence CPU, with an embedded Linux operation system.ResultsThe interlock logic and heartbeat functions were tested with all functions ok. Time consumption has been measured thoroughly since the important requirement, which is around 15 ms to stop the beam.ConclusionsMPS was completed in Sep. 2017 and then put into operation. It has been operating smoothly for more than 3 years. MPS has played an important role in every stage of CSNS’s commissioning and operation and achieved high reliability during the user’s experiment operation. The accelerator recently runs stably with low equipment failure.

J-PARC 3-GeV RCS: 1-MW beam operation and beyond

The J-PARC 3-GeV rapid cycling synchrotron (RCS) has recently achieved a 1-MW beam operation with considerably low fractional beam loss of a couple of 10−3 as a result of continuous efforts iterating experiments and numerical simulations. This success of the 1-MW beam operation opened a door to further beam power ramp-up beyond 1 MW; we are now promoting 1.2∼1.5-MW-equivalent high-intensity beam tests looking ahead to future upgrades at J-PARC. In this article, we first review the current status of beam loss in the 1-MW beam operation, then presenting the recent results of the 1.2-MW beam tests with particular emphasis on our approaches to beam loss issues. The beam intensity limit of the RCS is also discussed with well-established numerical simulations.

Effects of the Montague resonance on the formation of the beam distribution during multiturn injection painting in a high-intensity proton ring

The ``Montague resonance'' is a familiar issue in high-intensity proton rings, which causes emittance exchange between the two transverse planes, having a significant influence on their high-intensity performance. In this paper, we discuss the characteristic effects of this resonance on the formation of the beam distribution during multiturn injection painting that are measured experimentally at the 3-GeV rapid cycling synchrotron in the Japan Proton Accelerator Research Complex. In addition, we discuss an optimization methodology for injection painting for the case involving emittance exchange.

J-PARC H- ion source and space-charge neutralized LEBT for 100-mA high energy and high duty factor LINACs.

In July 2019, a design beam of 8.3 × 1013 protons/pulse, whose 25 Hz operation produced the design beam power of 1 MW, was accelerated for 10.5 h by using the J-PARC 3 GeV rapid cycling synchrotron. During the operation, a J-PARC H- ion source and a 400 MeV linear accelerator (LINAC) were operated with the design beam duty factor (BDF) of 1.25% (0.5 ms × 25 Hz) and ejected beam intensities of 58 mA and 50 mA, respectively. Furthermore, as expected from the transverse emittances measured in an H- ion source test-stand, they were successfully operated with the BDF of 1.5% (0.6 ms × 25 Hz) and ejected beam intensities of 72 mA and 60 mA, respectively. In the operation, the beam pulse accelerated by the J-PARC radio-frequency quadrupole LINAC (RFQ) had a rapid rise-time of about 10 µs and an excellent flatness with a slow variation of ±0.2%. A flat beam pulse was produced by the predicted 100% space-charge neutralization (SCN) in the upstream half of the J-PARC low-energy beam transport (LEBT) with a vacuum pressure of 3.6 × 10-4 Pa and the unpredicted high and almost constant SCN of about 69% in the downstream half of the LEBT with a vacuum pressure of 2.8 × 10-5 Pa. The rapid rise-time was produced by the preformed 100% SCN with a preceding 100 µs 40 keV beam, which was not accelerated by the RFQ due to the low energy outside the RFQ acceptance. In the test-stand operated with the terminal voltage of 62 kV and BDF of 5% (1 ms × 50 Hz), the transverse emittances of a 100-mA beam were also measured to be suitable for the RFQs of high energy LINACs. A 100-mA high energy and high duty factor LINAC could be realized with this source since the transverse emittances were further improved by about 8% with the shortest beam extractor in the test-stand.

Progress status in fabrication of HBC stripper foil for 3-GeV RCS at J-PARC in Tokai site

In the 3-GeV Rapid Cycling Synchrotron (RCS) at Japan Proton Accelerator Research Complex (J-PARC), we adopted thick Hybrid type Boron-doped Carbon (HBC) stripper foil for multi-turn H- charge-exchange injection. The HBC stripper foil developed at KEK has demonstrably improved the foil lifetime significantly. In addition, Graphite Thin Films (GTF) developed by KANEKA corp. was attempted to use for user operation. The GTF is a multilayer graphene sheet and it is expected to be a new candidate for highly durable charge stripping foil. HBC and GTF foils can be both employed the J-PARC RCS for long-term user operation. Early manufacturing of the stripper foil for the J-PARC was carried out according to the following two steps: foil fabrication at the KEK Tsukuba site and foil preparation at the JAEA Tokai site. Recently, the HBC foil deposition apparatus was relocated from KEK to JAEA, and new HBC foils were fabricated at the Tokai site. The performance of the new HBC foil was verified to be equivalent to the original HBC foil with offline beam irradiation tests. Furthermore, the use of the new HBC foils was successfully demonstrated during RCS user beam operation for one week.

New Design of Vacuum Chambers for Radiation Shield Installation at Beam Injection Area of J-PARC RCS

One of the issues in the J-PARC 3 GeV rapid cycling synchrotron is the high residual radiation dose around the beam injection point. A radiation shield is necessary to reduce radiation exposure of workers when maintenance is performed there. A space to install the radiation shield should be secured by newly designing a structure of the vacuum chamber at the injection point and the alumina ceramics beam pipes for the shift bump magnets. To make the space for the shield, the chamber is lengthened along the beam line and the cross-sectional shape is changed from circle to rectangle. The displacement and inner stress of the vacuum chamber due to atmospheric pressure were evaluated to be enough small by the calculation. For the ceramics beam pipe’s rf-shield, the damping resistor was effective to reduce the induced modulation voltages by the pulsed magnetic field.

Energy measurement and correction for stable operation in J-PARC

In Japan Proton Accelerator Research Complex (J-PARC), the beam accelerated up to 400MeV in the Linac is injected to 3 GeV rapid cycling synchrotron (RCS), and we realize the high intensity beam by using multi-turn injection. During a user operation, we rarely detected the beam loss at the high dispersion area in the RCS or the beam collimator section in the extraction beam transport line. These incidents indicate that the beam loss is caused by the momentum shift of RCS injection beam according to the experimental and simulated data. In the beam commissioning, we check the Linac beam momentum just before a user operation of the RCS. However, we could not previously measure the Linac beam momentum during the user operation because we adopt the multi-turn injection with synchrotron oscillation for longitudinal plane. Therefore, we measured the beam momentum in the beam injection line of the RCS. Because the Linac-to-3-GeV-RCS Beam Transport line (L3BT) has the high dispersion areas, we estimated the RCS-injection momentum from the beam orbit data by the Beam Position Monitors (BPMs). We measured the beam position data by these BPMs, and estimated the momentum shift by using the data and beam simulation. As a result, we found the momentum fluctuation during the user operation, and the fluctuation ∆p/p was shifted up to 0.1% from the reference. In addition, to suppress this beam loss induced by the momentum fluctuation and shift, we developed the momentum correction system. The fluctuation was achieved less than ±0.02 % with this system. Finally, the beam loss incidents induced by the beam momentum shift does not occur, and we successfully achieved the more stable user operation in J-PARC.

J-PARC RCS: high-order field components inherent in the injection bump magnets and their effects on the circulating beam during multi-turn injection

We investigated the cause of the residual beam loss during multi-turn injection of the J-PARC 3-GeV rapid cycling synchrotron (RCS). In the RCS, four sets of injection bump magnets (pulsed dipole magnets) are employed for multi-turn injection. Numerical simulations considering the actual magnetic field profiles of the injection bump magnets well reproduced the empirical beam loss, and pointed that a 3rd-order random betatron resonance driven by a sextupole field component inherent in the injection bump magnets is the major source of the beam loss. In this paper, we describe the detailed mechanism of emittance growth and beam loss caused by such a high-order field component of the injection bump magnets including their correction scenario.

Longitudinal Measurements and Beam Tuning in the J-PARC Linac MEBT1

The Japan Proton Accelerator Research Complex (J-PARC) linac is operated with design peak current of 50 mA from 2018. For operation with such a high beam current, it is important to understand transverse and longitudinal beam properties especially in low-velocity region. A medium energy beam transport (MEBT1) line between the 3-MeV radio-frequency quadrupole linac (RFQ) and the 50-MeV drift-tube linac (DTL) is a 3-m-long transport line to match the beam to the DTL and produces a macro pulse configuration for a 3-GeV rapid-cycling synchrotron (RCS). In this paper, recent measurements and beam tuning results in MEBT1 will be presented.

Iterative learning control-based adaptive beam loading compensation implementations in the J-PARC LINAC

Abstract The Japan Proton Accelerator Research Complex (J-PARC) is a multi-purpose high-intensity proton accelerator facility that consists of a 400 MeV linear accelerator (LINAC), a 3 GeV rapid-cycling synchrotron (RCS), a 30 GeV main ring synchrotron (MR), and experimental facilities. In 2018, to achieve the goal of a 1 MW beam power at the RCS, the beam current of the LINAC was increased from 30 to 50 mA. Based on the beam loading effect, such a strong beam current can cause a significant drop in the accelerating gradients. Although both feedback and normal static feedforward control schemes were used in the low-level radio frequency (LLRF) system to suppress the beam loading effect, the peak-to-peak stability of the RF field still does not meet the requirements of the LINAC (i.e., ± 0.5% amplitude and ± 0 . 5 ° phase). To solve this problem, an iterative learning control (ILC) scheme was studied and implemented in the J-PARC LINAC. The beam loading compensation experiments demonstrate that the inclusion of the ILC controller improves the performance of the control system significantly. As the number of iterations increase, the tracking error of the system decreases monotonously. For the accelerating field with beam operation, compared to the performance with static feedforward control, the peak-to-peak stability of amplitude improves from greater than ± 1% to less than ± 0.4%, and the peak-to-peak stability of phase improves from ± 1°to ± 0 . 2 ° .

ORBIT Simulation, Measurement and Mitigation of Transverse Beam Instability in the Presence of Strong Space Charge in the 3-GeV RCS OF J-PARC

The transverse impedance of eight extraction pulse kicker magnets (KM) is a strong beam instability source in the 3-GeV RCS (Rapid Cycling Synchrotron) at J-PARC (Japan Proton Accelerator Research Complex). Significant beam instability occurs even at a half of the designed 1 MW beam power when the chromaticity (ξ) is fully corrected for the entire acceleration cycle up to 3 GeV, but no beam instability occurs if the ξ is fully corrected only at the injection energy of 0.4 GeV. To realize the designed 1 MW beam power, collective beam dynamics with including the space charge effect for the coupled bunch instabilities excited by the KM impedance and associated measures were studied by incorporating all realistic time-dependent machine parameters in the ORBIT 3-D particle tracking code. The simulation results for systematic beam instability studies and its mitigation measures were found to be very consistent with measurements and, as a consequence, an acceleration of 1 MW beam power has been successfully achieved.