Rapid Cycling Synchrotron Research Articles

World's Strongest Pulsed Muon Beam Achieved at J-PARC MUSE

The muon science facility (MUSE, abbreviation of MUon Science Establishment), along with the neutron, hadron, and neutrino facilities, is under construction at the Japan Proton Accelerator Research Complex (J-PARC) in Tokai. The MUSE facility is located in the Materials and Life Science Experimental Facility (MLF), which is a building integrating both neutron and muon science programs. About 85% of the 3 GeV, 333 μA (1 MW) beam from the Rapid Cycle Synchrotron (RCS) is sent to the MLF for the production of intense pulsed neutron and muon beams, while the remaining 15% is sent to the 50 GeV ring for further acceleration for the kaon and neutrino physics programs.

中国散裂中子源/快循环质子同步加速器射频同步相位环路的数字化控制

中国散裂中子源/快循环质子同步加速器射频同步相位环路的数字化控制

Design Study on Slow Beam Extraction in the 1 GeV Rapid Cycling Synchrotron at the PEFP

in a slow extraction system for a future 1-GeV proton synchrotron the Proton Engineering Frontier Project. This paper describes the properties of the optics design and optimizations for slow extraction in the synchrotron. The eects of the thirdinteger resonance in Rapid Cycle Synchrotron were investigated. We performed beam tracking simulations to observe the motions of particles in phase space by using the Methodical Accelerator Design 8 program. Finally, we performed beam trace simulations at the designed slow extraction line and showed that the proton beam could be stably extracted by using the RCS.

Studies of dual-harmonic acceleration at CSNS- II

The Rapid Cycling Synchrotron RCS) of the China Spallation Neutron Source (CSNS) complex is designed to provide 1.56×1013 protons per pulse (ppp) during the initial stage, and it is upgradeable to 3.12×1013 ppp during the second stage and 6.24×1013 ppp during the ultimate stage. The high beam intensity in the RCS requires alleviation of space charge effects to reduce beam losses, which is key in such high beam power accelerators. With higher intensities in the upgrading phases, a dual-harmonic RF system is planned to produce flat-topped bunches that are useful to reduce the space charge effects. We have studied different schemes to apply the dual-harmonic acceleration in CSNS- II, and have calculated the main parameters of the RF systems, which are presented in this paper.

The origin of magnetic alloy core buckling in J-PARC 3 GeV RCS

We have been operating ten RF cavities loaded with magnetic alloy (MA) cores with a high field gradient of more than 20 kV/m in Japan Proton Accelerator Research Complex (J-PARC) 3 GeV Rapid Cycling Synchrotron (RCS) since September 2007. During 3 years operation, we detected three times the impedance reductions of RF cavities resulting from the buckling of MA cores. To find out the origin of the MA core buckling, we evaluated the thermal stress inside the MA cores in operation and studied the relationship between the MA core buckling and core structure. We figured out that the MA core buckling was caused by the thermal stress that was enhanced due to the impregnation with low viscosity epoxy resin. We improved the MA cores without the low viscosity epoxy resin impregnation and replaced all the cores in one RF cavity with them in March 2010. Up to now we operated the RF cavity loaded with the improved MA cores for 1500 h, it showed no impedance reduction and no buckling.

Beam Collimation in PEFP RCS

This work is related with the beam collimation in the injection period of the proton engineering frontier project (PEFP) rapid cycling synchrotron (RCS).The two-stage collimation scheme was used with two rectangular collimators. We studied the collimation efficiency in various collimator conditions and optimized the collimation systemin order to minimize the uncontrolled beam losses.

Dynamic Measurement System for Dipoles of RCS for CS

A dynamic measurement system was developed by the Institute of Modern Physics (IMP) for the dipole prototype of Rapid Cycle Synchrotron (RCS) of China Spallation Neutron Source (CSNS). The repetition frequency of RCS is 25 Hz. The probe is a moving arc searching-coil, and the data acquisition system is based on the dynamic analysis modular of National Instrument. To get the error of high order harmonics of the field at basic frequency, the hardware integrator is replaced by a high speed ADC with software filter and integrator. A series of harmonic coefficients of field are used to express the varieties of dynamic fields in space and time simultaneously. The measurement system has been tested in Institute of High Energy Physics (IHEP), and the property of the dipole prototype of RCS has been measured. Some measurement results and the repeatability of system are illustrated in this paper.

Field Measurement and Machinery Placement of the J-PARC RCS Magnets

The 3 GeV synchrotron in the Japan Proton Accelerator Research Complex (J-PARC) is a rapid-cycling synchrotron (RCS), which accelerates a high-intensity proton beam from 400 MeV to 3 GeV at a repetition rate of 25 Hz. RCS is composed of 24 dipole magnets, 60 quadrupole magnets and 18 sextupole magnets. Field measurement was performed for all magnets and adequate results were obtained. In this paper, we will report the results of field measurement and machinery placement of the magnets performed based on those results.

Design and Circuit Simulation of a Magnetic Switching System for Kicker Magnet Power Supply of 3 GeV RCS in J-PARC

A magnetic switching system replacing thyratron of the kicker magnet power supply in the J-PARC 3 GeV rapid cycling synchrotron (RCS) was studied for stable operation. The core of the magnetic switch is required to have a square B-H loop as an ideal switch. Nano-crystalline alloy (Finemet; FT-1H) was selected for the magnetic core. B-H curves at high magnetization rate (dB/dt) were measured. Magnetization rate dependence of magnetic field and permeability were evaluated based on magnetic domain models. We speculate that the magnetization progress is dominated by the bar-domain mode in the range of magnetization rate we measured. Low leakage current of the magnetic core before saturation flows to the kicker magnets. Closed orbit distortion, , in the RCS caused by the leakage current was evaluated. Calculated results show that the can be suppressed sufficiently. A circuit of the magnetic switching system was designed. A Spice model of the magnetic switching system is described and the simulation results are shown.

Design and Prototype Test of CSNS/RCS Injection and Extraction Magnets

The China Spallation Neutron Source (CSNS) accelerator consists of a linear accelerator (Linac), a rapid cycle synchrotron (RCS) and two beam transport lines. The injection and extraction systems of the RCS play an important role in connecting these four parts of accelerator. The injection system consists of three sets of bump magnets and two septum magnets, and the extraction system is composed of ten fast kicker magnets and a Lambertson magnet. The design of all these magnets is carefully considered. To prove the design concepts, a prototype bump magnet and a prototype kicker magnet have been successfully developed and tested.

Simulation of longitudinal beam manipulation during multi-turn injection in J-PARC RCS

In a high intensity proton synchrotron the longitudinal beam emittance should be controlled to alleviate space charge effects at the injection. At the rapid cycling synchrotron in J-PARC our goal is to obtain and keep a high bunching factor during and after multi-turn injection. We have investigated the dependence of the bunching factor on second harmonic rf content, momentum offset, and second harmonic phase sweep. We found an optimum condition of the combination of these longitudinal rf manipulations that results in a flat bunch shape after injection.

J-PARC muon facility, MUSE

The muon science facility (MUSE, abbreviation of MUon Science Establishment), along with the neutron, hadron, and neutrino facilities, is one of the experimental areas of the J-PARC project, which was approved for construction in a period from 2001 to 2008. The MUSE facility is located in the Materials and Life Science Facility (MLF), which is a building integrated to include both neutron and muon science programs. Construction of the MLF building was started in the beginning of 2004, and was completed at the end of the 2006 fiscal year. For Phase 1, we managed to install one super-conducting decay/surface muon channel with a modest-acceptance (about 45 mSr) pion injector in the summer of 2008. Finally, on September 19th, 2008, the 20 mm thick edge-cooled, non-rotating graphite target, which is surrounded by a copper frame, was, for the first time, placed into the 3GeV proton beam obtained from the rapid cycling synchrotron (RCS). The nuclear reactions between the 3 GeV proton beam and the nucleus of carbon produce both positively (π+) and negatively (π−) charged pions. On September 26th, 2008, we finally succeeded to extract? surface muons (μ+), which are obtained from the decay of π+ near the surface of the pion production target in the proton beam line. First, we commissioned the secondary muon beam line optics by tuning the superconducting magnet, the quadrupole and bending magnets, and the DC separator in order to optimize the transport of the surface muon beam and to eliminate the e+ contamination. Then, on December 25th, 2008, we also succeeded in the extraction of the "decay muons (μ+/μ-)", which are obtained through the in-flight decay of π+/π−

Development of an H− ion source for Japan Proton Accelerator Research Complex upgrade

A cesium (Cs) free H(-) ion source driven with a lanthanum hexaboride (LaB(6)) filament was adopted as an ion source for the first stage of the Japan Proton Accelerator Research Complex (J-PARC). At present, the maximum H(-) ion current produced by the ion source is 38 mA, using which J-PARC can produce a proton beam power of 0.6 MW by accelerating it with the 181 MeV linac and the 3 GeV rapid cycling synchrotron. In order to satisfy the beam power of 1 MW required for the second stage of the J-PARC in the near future, we have to increase the ion current to more than 60 mA. Therefore, we have started to develop a Cs-seeded ion source by adding an external Cs-seeding system to a J-PARC test ion source that has a structure similar to that of the J-PARC ion source except for the fact that the plasma chamber is slightly larger. As a result, a H(-) ion current of more than 70 mA was obtained from the ion source using a tungsten filament instead of a LaB(6) filament with a low arc discharge power of 15 kW (100 V, 150 A).

Current Status and Performance of the J-PARC Accelerators

J-PARC (Japan Proton Accelerator Research Complex) is a multi-purpose research facility for materials and life sciences, nuclear and particle physics, and nuclear engineering with extremely high power proton beams of 1 MW. The accelerator complex consists of a 400-MeV linac, a 3-GeV Rapid Cycling Synchrotron (RCS), and a 50-GeV Main Ring synchrotron (MR). Its goals are to provide MW-class beams at 3 GeV and at several 10 GeV, while it is a challenge to localize and suppress beam loss to the level to allow hands-on maintenance of accelerator components. The RCS scheme is adopted to realize them, which is advantageous over conventional Accumulation Ring (AR) regarding less beam loss problems due to lower beam current and easier construction and operation of a linac. RCS, however, required various challenging technologies such as ceramic ducts to reduce eddy current effects, high field Radio Frequency (RF) system, and paint injection technique (an injection scheme to reduce phase space density of the beam) to reduce space charge effects. The linac has also unique technologies to minimize beam loss, such as compact electromagnet Drift Tube Quadrupoles (DTQ’s) to control beam envelopes precisely, and a fast beam suspending system in Machine Protection System (MPS) with Radio Frequency Quadrupole linac (RFQ). The beam commissioning of the linac started in Nov. 2006, and its design energy of 181 MeV in the first construction phase was achieved in Jan. 2007. RCS beam commissioning started in Sep. 2007 and the beam was accelerated to the designed energy of 3 GeV in Oct. 2007. MR beam commissioning started in May 2008, and the beam acceleration to 30 GeV was established in Dec. 2008. The first neutron and muon beams were produced in May and Sep. 2008, respectively, at Materials and Life science experimental Facility (MLF). The linac commissioning has resulted in very stable beam with short down time. RCS commissioning quickly achieved beam acceleration and extraction, and paint injections are being studied intensively. RCS recorded the highest beam power of 0.21 MW in Sep. 2008 with beam loss well localized at the collimators. The linac beam energy will be upgraded to 400 MeV with Annular Coupled Structure linac (ACS) in order to increase the beam power to 1 MW. In the second construction phase, upgrade of the linac with 600-MeV Super-Conducting Linac (SCL) for Accelerator-Driven nuclear waste transmutation System (ADS) and upgrade of MR energy from 30 to 50 GeV are planned.Copyright © 2009 by ASME

Estimation of Eddy Current Loss for a Turbo-molecular Pump in the J-PARC Rapid Cycling Synchrotron

Magnetically suspended turbo-molecular pumps (TMPs) have been widely used in nuclear fusion devices and sometimes used in particle accelerators, because it is much easier for the TMPs with dry backing pumps to achieve and maintain UHV without oil contamination. In these devices the TMPs are influenced by a quasi static magnetic field; the eddy current is induced on the rotating rotor and then forces the rotor to thermally expand. In order to use the TMPs safely we attempted to establish a standard procedure for determining the influence of magnetic fields on TMPs. First of all, this influence was investigated in detail through the experiment with a rather small TMP. As a result, the following are found. (1) The parallel magnetic field has no influence, on the other hand, the driving power and the rotor temperature are greatly affected by the vertical magnetic fields. (2) The eddy current loss is formulated and well estimated with a model where a localized magnetic field and current flow exist within the rotor into the region down to a substantial skin depth δ from the surface. This time we applied the above conclusions to the TMPs with high radioactive resistance which were employed in the 3-GeV rapid cycling synchrotron (RCS) in J-PARC (Japan Proton Accelerator Research Complex). With the evaluation equation of eddy current loss established through the experiment in a uniform magnetic field, the rise of rotor temperature is estimated to be ∼100°C even in the orthogonal magnetic field of 0.003 T. Thus, we concluded that the TMPs are safely operated in the RCS, as the leakage magnetic field at the floor where the TMPs are set is less than 0.001 T.

The Development of a Pirani Vacuum Gauge with a Platinum Wire in the J-PARC 3-GeV Rapid Cycling Synchrotron

The back pressure of Turbo-Molecular Pumps (TMPs) is constantly monitored using Pirani gauges at J-PARC (Japan Proton Accelerator Complex) RCS (3-GeV Rapid Cycling Synchrotron) where they are used not only in rough pumping but also evacuations during beam operations. The gauge head needs to be very resistant to vibration and abrupt air inlet etc. in minimizing exposure to radiation during maintenance and hence a 50 μm in diameter W wire was adopted as the filament. This type of Pirani gauge has worked well in monitoring the back pressure of the TMP but it has become difficult to measure the low pressure of less than several Pa with the gauge, which may have been due to changes in the emissivity of the W surface. An attempt was therefore made to develop a gauge head made of Pt wire in allowing pressures as low as 0.1 Pa to be measured. Platinum is one of the best possible materials to use because it is very stable against oxidization. However, ordinary Pt gauge heads are rather weak when it comes to vibrations and abrupt air inlet due to its low tensile strength. In order to improve its toughness the filament was composed of twelve 100 μm in diameter Pt wires that were 65 mm long, resulting in it being capable of enduring a force of 25 N. All the wires were welded in series on metal poles in two separate glass plates, with the poles being electrically insulated. This resulted in the filament, 78 cm long and about 10 Ω at room temperature, being containable in a 5 cm in diameter and 10 cm long cylindrical envelope. The output from the gauge head was then examined as a function of pressure under constant current as the plan was for it to be controlled using the constant current method. Confirmation then took place that the pressures of 0.1 Pa up to 103 Pa were measurable with the gauge using current control in such way that the set value increased with pressure increases in three stages.

High-Intensity Proton Accelerators

The construction of the J-PARC facility [1] was started in 2001 as a joint venture between KEK (High Energy Accelerator Research Organization) and JAERI (Japan Atomic Energy Research Institute, which was reorganized as JAEA (Japan Atomic Energy Agency) in 2005). The J-PARC facility is composed of a 400 MeV linac [2], a 3 GeV rapid cycling synchrotron (RCS) [3], and a 50 GeV synchrotron (MR, the beam energy is at present 30 GeV) [4], a materials and life science experimental facility, a hadron experimental facility, and a neutrino experimental facility as shown in Figure 1. The neutrino facility sends a neutrino beam to Super KAMIOKANDE. The beam commissioning to the beam lines planned at the first step had been successfully achieved as shown in Figure 2.

Radiation Shielding of a Beta-Beam Rapid Cycling Synchrotron

In a future beta-beam facility, radioactive ions (namely, 6He and 18Ne) are produced, accelerated, and then stored in a large decay ring, where they eventually produce neutrino beams through beta decay. Radiation protection is of great concern for this facility because decay products are present at all energies along the accelerator chain.Experimental data on radioactivity produced by ion accelerators are still poor, and few Monte Carlo codes can transport ions. All present calculations are performed with the Monte Carlo code FLUKA. The radiation environment generated by ion beam losses is compared with the available experimental data. The attenuation length of radiation in concrete is calculated for 6He and 18Ne at four different energies, from 100 to 1650 MeV/u.A preliminary shielding design for the Rapid Cycling Synchrotron, purpose-designed for a beta-beam accelerator chain at CERN, is proposed.

China Spallation Neutron Source - an overview of application prospects

The China Spallation Neutron Source (CSNS) is an accelerator-based multidisciplinary user facility to be constructed in Dongguan, Guangdong, China. The CSNS complex consists of an H− linear accelerator, a rapid cycling synchrotron accelerating the beam to 1.6 GeV, a solid-tungsten target station, and instruments for spallation neutron applications. The facility operates at 25 Hz repetition rate with an initial design beam power of 120 kW and is upgradeable to 500 kW. Construction of the CSNS project will lay the foundation of a leading national research center based on advanced proton-accelerator technology, pulsed neutron-scattering technology, and related programs including muon, fast neutron, and proton applications as well as medical therapy and accelerator-driven subcritical reactor (ADS) applications to serve China's strategic needs in scientific research and technological innovation for the next 30 plus years.

Investigation of the vertical instability at the Argonne Intense Pulsed Neutron Source

The rapid cycling synchrotron of the intense pulsed neutron source at Argonne National Laboratory normally operates at an average beam current of 14 to 15 � A, accelerating protons from 50 to 450 MeV 30 times per second. The beam current is limited by a single-bunch vertical instability that occurs in the later part of the 14 ms acceleration cycle. By analyzing turn-by-turn beam position monitor data, two cases of vertical beam centroid oscillations were discovered. The oscillations start from the tail of the bunch, build up, and develop toward the head of the bunch. The development stops near the bunch center and oscillations remain localized in the tail for a relatively long time (2–4 ms, 1–2 � 10 4 turns). This vertical instability is identified as the cause of the beam loss. We compared this instability with a head-tail instability that was purposely induced by switching off sextupole magnets. It appears that the observed vertical instability is different from the classical head-tail instability.