High Intensity Proton Synchrotron Research Articles

Commissioning and operation of the transverse collimation system at the RCS of CSNS

In high-intensity proton synchrotrons, controlling beam loss during machine operation is crucial to prevent radiation damage. Uncontrolled beam loss poses a significant challenge in achieving higher beam intensity and power in these synchrotrons. The beam collimation system plays a vital role in removing halo particles and localizing beam loss, serving as a critical tool for controlling uncontrolled beam loss in high-intensity proton accelerators. To address the issue of uncontrolled beam loss, a two-stage transverse collimation system was designed at the rapid cycling synchrotron (RCS) of China Spallation Neutron Source (CSNS). However, during the beam commissioning, it was found that the collimation efficiency was compromised due to the small ratio of the physical acceptance to the collimator acceptance and insufficient phase advances between the primary and secondary collimators. To address this issue, the designed two-stage collimator was modified to a one-stage collimator. Through optimization of the collimation system, the beam loss was effectively localized within the collimator area. As a result, CSNS achieved the design power of 100 kW with minimal uncontrolled beam loss.

Development of dual-harmonic RF system for CSNS-II

The upgrade of the China Spallation Neutron Source (CSNS-II) encompasses the development of a dual harmonic RF system for the Rapid Cycling Synchrotron (RCS). The objective of this system is to achieve a maximum second harmonic voltage of 100 kV. To meet this requirement, a high gradient cavity is being used in place of the traditional ferrite loaded cavity. Magnetic alloy (MA) loaded cavities, which can attain very high field gradients, have demonstrated their suitability for high-intensity proton synchrotrons. As a result, designing an RF system with MA-loaded cavities has emerged as a primary focus. Over the past decade, substantial advancements have been made in the development of MA-loaded cavities at CSNS. This paper provides an overview of the RF system that incorporates the MA-loaded cavity and presents the high-power test and beam test results of the system.

Multifold bunch splitting in a high-intensity medium-energy proton synchrotron

Bunch splitting is an RF manipulation method of changing the bunch structure, bunch numbers and bunch intensity in a high-intensity synchrotron that serve as the injector for a particle collider. An efficient way to realize bunch splitting is to use the combination of different harmonic RF systems, such as the two-fold bunch splitting of a bunch with a combination of fundamental harmonic and higher harmonic RF systems. The two-fold bunch splitting and three-fold bunch splitting methods have been experimentally verified and successfully applied in the CERN PS. In this paper, a generalized multifold bunch splitting method is given. The five-fold bunch splitting method using specially designed multi-harmonic RF systems was studied and tentatively applied to the medium-stage synchrotron (MSS), the third accelerator of the injector chain of the Super Proton-Proton Collider (SPPC), to mitigate the pileup effects and collective instabilities of a single bunch in the SPPC. The results show that the five-fold bunch splitting is feasible and both the bunch population distribution and longitudinal emittance growth after the splitting are acceptable, e.g., a few percent in the population deviation and less than 10% in the total emittance growth. Intensity-related effects and beam feedback issues during the splitting process have also been addressed.

Multi-Ribbon Profile Monitor for high power proton beam at J-PARC MR Abort Line

Japan Proton Accelerator Research Complex (J-PARC) Main Ring (MR), the world-class high intensity proton synchrotron, provides proton beam to two experimental facilities with two extraction modes: Fast extraction (FX) and Slow extraction (SX). The number of protons per pulse (ppp) in MR recorded the world highest value of 2.7 × 1014 in the FX mode. Now we are planning to increase the ppp further up to 3.3 × 1014 in near future. The beam profile is one of the most important parameters to discuss the high intensity beam dynamics in MR. Monitors using multi-wires /ribbons are effective to measure the beam profile with good accuracy and wide dynamic range. However, they cause significant beam losses by interactions with high-intensity circulating beam in synchrotrons. Recently, we installed new multi-ribbon profile monitor (MRPM) in an abort line in MR. The abort line is one of the extracted beam lines of the FX system. It has a quadrupole doublet which is called Abort Q and transports extracted beam to a beam dump. The FX system can extract the circulating beam in MR with an arbitrary energy. Performing the single-pass measurement with MRPM and changing the transfer matrix by sweeping field strength of Abort Q, the emittance of the extracted beam can be measured. In this paper, we present the design, manufacturing, and results of the first beam test of newly installed MRPM system.

Capacitor bank of power supply for J-PARC MR main magnets

The main ring (MR) of the Japan Proton Accelerator Research Complex (J-PARC) is a high-intensity proton synchrotron that supplies proton beams for the long-baseline neutrino experiment, called the Tokai to Kamioka (T2K). To satisfy the experimental condition for the T2K, the increase in the present beam power of 450 kW to 750 kW and beyond is mandatory. The scheme of the high-repetition-rate operation is adopted for the MR upgrade. The repetition cycle is planned to be shortened from 2.48 s at present to 1.28 s in this scheme. This upgrade involves the increase in the power variation of the electrical system. To suppress the power variation, an energy storage that consists of capacitor banks (CBs) was developed and installed in the power supply of the main magnets, since the main magnets are the primary source of power variation. The CB was designed with a sufficient consideration to avoid serious failures. The number of fuses were installed in the CB to avoid energy concentration on a short-circuited capacitor. The scheme for the safe dissipation of the concentrated energy was also employed. A fuse arcing test was carried out to clearly show the fuse reliability since the CB safety is strongly dependent upon the fuses.

Secondary electron emission characteristics of graphene films with copper substrate**Supported by the National Natural Science Foundation of China (11475166) National Natural Science Foundation of China (11205155) and National Natural Science Foundation of China (11575214).

For modern and future circular accelerators, especially high-intensity proton synchrotrons or colliders, the electron cloud effect is a key issue. So, in order to reduce the electron cloud effect, exploring very low secondary electron yield (SEY) material or coating used in vacuum tubes becomes necessary. In this article, we studied the SEY characteristics of graphene films with different thicknesses which were deposited on copper substrates using chemical vapor deposition. The SEY tests were done at temperatures of 25 °C and vacuum pressure of (2 − 6) × 10−9 torr. The properties of the deposited graphene films were investigated by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The SEY curves show that the number of graphene layers has a great effect on the SEY of graphene films. The maximum SEY of graphene films decreases with the increase of the number of layers. The maximum SEY of 6–8 layers of graphene film is 1.25. These results have a great significance for next-generation particle accelerators.

Development and applications of a multi-purpose digital controller with a System-on-Chip FPGA for accelerators

J-PARC Main Ring (MR) is a high intensity proton synchrotron which accelerates protons from 3GeV to 30GeV. It has operated at a beam intensity of 390kW and an upgrade toward the megawatt rating is scheduled. For higher beam intensity, some of the accelerator components require more intelligent and complicated functions. To consolidate such functions among various components, we developed multi-purpose digital boards using a System-on-Chip Field-Programmable Gated Array (SoC FPGA). In this paper, we describe the details of our developed boards as well as their possible applications. As an application of the boards, we have successfully performed the measurement of the betatron amplitude function during beam acceleration in J-PARC MR. The experimental setup and results of the measurement are also described in detail.

Theoretical study of a dual harmonic system and its application to the CSNS/RCS**Supported by National Natural Science Foundation of China (11175193)

Dual harmonic systems have been widely used in high intensity proton synchrotrons to suppress the space charge effect, as well as reduce the beam loss. To investigate the longitudinal beam dynamics in a dual rf system, the potential well, the sub-buckets in the bunch and the multi-solutions of the phase equation are studied theoretically in this paper. Based on these theoretical studies, optimization of bunching factor and rf voltage waveform are made for the dual harmonic rf system in the upgrade phase of the China Spallation Neutron Source Rapid Cycling Synchrotron (CSNS/RCS). In the optimization process, the simulation with space charge effect is done using a newly developed code, C-SCSIM.

Study on the effects of chromaticity and magnetic field tracking errors at CSNS/RCS

The Rapid Cycling Synchrotron (RCS) is a key component of the China Spallation Neutron Source (CSNS). For this type of high intensity proton synchrotron, the chromaticity, space charge effects, and magnetic field tracking errors between the quadrupoles and the dipoles can induce beta function distortion and tune shift, and induce resonances. In this paper, the combined effects of chromaticity, magnetic field tracking errors and space charge on beam dynamics at CSNS/RCS are studied systemically. 3-D simulations with different magnetic field tracking errors are performed by using the code ORBIT, and the simulation results are compared with the case without tracking errors.

Rapid Cycling Synchrotrons and Accumulator Rings for High-Intensity Hadron Beams

Boosted by the needs in high-energy physics and nuclear physics and also multidisciplinary applications, high-intensity proton synchrotrons and accumulator rings have been developed quickly around the world over the last 30 years. New projects and plans are proposed with even higher beam power. The proton beam power has increased from less than 10 kW in the 1970s to about 1 MW level today, and the required beam power in the coming decade is a few MW. This article reviews the achievements in designing and constructing rapid cycling synchrotrons (RCSs) and accumulator rings (ARs) and the future development trends, principally on proton beams but also including heavy ion beams. It presents the evolution of RCS and AR machines, today's design philosophy, relevant accelerator physics, and also state-of-the-art accelerator technology.

Kaon experiments at J-PARC

The newly constructed high-intensity proton synchrotron, J-PARC ( J apan P roton A ccelerator R esearch C omplex), has completed its first stage of construction and started accelerator commissioning. Many experiments using slowly extracted proton beam are proposed and being prepared. Among them, two experiments to study Kaon decays, KOTO to search for a K L → π 0 ν ν ¯ decay and TREK for violation of Time-Reversal invariance, are under preparation. In this article, current status of the experiments is reported.

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.

Particle tracking study of the injection process with field interferences in a rapid cycling synchrotron

The large-bore magnets in the injection system of a high-intensity proton synchrotron are placed close to each other as compared to their bore sizes. In such cases, the magnetic cores interfere with the fringe fields of adjacent magnets. Moreover, the incoming beam passes through several kinds of time-varying fields along the injection line and the nonlinear field region of the ring quadrupole magnet. The beam behavior under these conditions is analyzed by using the Runge-Kutta method. Although the interference of the magnetic fields does not result in emittance growth, it produces a closed-orbit distortion. Field fluctuations of the time-varying field cause an emittance growth and the nonlinear field deforms the beam profile in phase space of the incoming beam. These effects lead to the modification of the injection scheme. This study focuses on the particle tracking with magnetic field interferences during the early stage of beam commissioning, when the space charge force is not important.

Lattice Design and Electron Cloud Instability in a High-Intensity Proton Synchrotron

Lattice Design and Electron Cloud Instability in a High-Intensity Proton Synchrotron Eun-San Kim Department of Physics, Kyungpook National University, Daegu 702-701 (Received 7 January 2008) The proton accelerators for the neutron spallation source and nuclear experiments usually consist of a high-intensity linac and a synchrotron. An important issue in such a high intensity accelerator is to keep particle losses by beam injection from the linac and beam instabilities in the synchrotron down to an acceptable level. We show the analysis results of optics design and beam dynamics for a 4-GeV high-intensity proton synchrotron. A lattice with a high transition gamma is chosen to avoid the beam loss at the transition crossing, and the stabilities on the lattice are also investigated by examining the e ects of machine errors. We investigate the characteristics of the electron cloud instability, which may limit the beam performance in the high-intensity proton synchrotron. We present the analysis on the beam dynamics in the proton synchrotron with a low injection energy of around 100 MeV. From these results, we present the results on the choice of injection beam energy and on the available beam power in terms of the space charge e ects and the electron cloud instability. PACS numbers: 29.27.Bd, 41.60.Ap, 29.17.+w

Ventilation en réanimation

The main ring (MR) of the Japan Proton Accelerator Research Complex (J-PARC) is a high-intensity proton synchrotron that supplies proton beams for the long-baseline neutrino experiment, called the Tokai to Kamioka (T2K). To satisfy the experimental condition for the T2K, the increase in the present beam power of 450 kW to 750 kW and beyond is mandatory. The scheme of the high-repetition-rate operation is adopted for the MR upgrade. The repetition cycle is planned to be shortened from 2.48 s at present to 1.28 s in this scheme. This upgrade involves the increase in the power variation of the electrical system. To suppress the power variation, an energy storage that consists of capacitor banks (CBs) was developed and installed in the power supply of the main magnets, since the main magnets are the primary source of power variation. The CB was designed with a sufficient consideration to avoid serious failures. The number of fuses were installed in the CB to avoid energy concentration on a short-circuited capacitor. The scheme for the safe dissipation of the concentrated energy was also employed. A fuse arcing test was carried out to clearly show the fuse reliability since the CB safety is strongly dependent upon the fuses.

Neutrino beamline for JHF-Kamioka long baseline experiment

The JHF-Kamioka neutrino project is a second generation long baseline neutrino oscillation experiment. A high intensity narrow-band neutrino beam is produced by secondary pions created by a high intensity proton synchrotron at JHF (JAERI). The neutrino energy is tuned to the oscillation maximum at ∼1 GeV for a baseline length of 295 km at the water Čerenkov detector, Super-Kamiokande. In this paper, the current design of the neutrino beam facility at JHF is described.

MeasuringCPviolation and mass ordering in joint long baseline experiments with superbeams

We propose to measure the $\mathrm{CP}$ phase ${\ensuremath{\delta}}_{\mathrm{CP}},$ the magnitude of the neutrino mixing matrix element $|{U}_{e3}|$ and the sign of the atmospheric scale mass-squared difference $\ensuremath{\Delta}{\mathrm{m}}_{31}^{2}$ with a superbeam by the joint analysis of two different long baseline neutrino oscillation experiments. One is a long baseline experiment (LBL) at 300 km and the other is a very long baseline (VLBL) experiment at 2100 km. We take the neutrino source to be the approved high intensity proton synchrotron, HIPA. The neutrino beam for the LBL is the 2-degree off-axis superbeam, and for the VLBL a narrowband superbeam. Taking into account all possible errors, we evaluate the event rates required and the sensitivities that can be attained for the determination of ${\ensuremath{\delta}}_{\mathrm{CP}}$ and the sign of $\ensuremath{\Delta}{m}_{31}^{2}.$ We arrive at a representative scenario for a reasonably precise probe of this part of neutrino physics.

Electron emission from ion bombarded stainless-steel surfaces coated and noncoated with TiN and its relevance to the design of high intensity storage rings

High intensity proton synchrotrons and proton storage rings are being designed with TiN coated vacuum components to reduce electron cloud buildup, which can lead to multipacting and instabilities. It has been established that when the surfaces are irradiated with energetic electrons, the TiN coatings reduce the electron cloud buildup because the TiN has a higher work function when compared to metallic surfaces. The present work investigates the electron emission from these coatings when the surface is bombarded with 28 MeV protons, 126 MeV oxygen ions, and 182 MeV gold ions. Understanding the electron emission from ion bombardment is important for the machine collimator regions, where the beam halo is removed.

An analytical formula for the band width of a strong nonstructure octupole resonance induced by a space charge

In a high intensity proton synchrotron nonstructure octupole resonances are excited by a space charge force when its designed periodicity is broken by quadrupole errors. This paper gives an analytical formula to calculate a band width of a nonstructure octupole resonance induced by a space charge force. Two kinds of modulations, beam envelope modulation and betatron-phase modulation are taken into account as perturbations. An approximated treatment shows that the phase modulation takes on a more important role. The formula is applied to the KEK-PS, at which the band widths of nonstructure octupole resonances induced by the space charge force are much larger than that produced by magnetic octupole errors.

Next generation antiproton facilities

Abstract A prospect for future antiproton facilities in the post-LEAR era is presented. The Antiproton Decelerator (AD) project, proposed as a reduced version of the LEAR complex, will be realized immediately after the scheduled closure of LEAR and regarded as the nearest intermediate step. In the long term scale a new antiproton facility will be created in connection with the proposed 50 GeV high-intensity proton synchrotron of the Japanese Hadron Project.