China Spallation Neutron Source Accelerator Research Articles

Performance and painting scheme considerations for the CSNS injection

The accelerator complex of China Spallation Neutron Source (CSNS) consists of an 80 MeV H- Linac and a 1.6 GeV proton rapid cycling synchrotron (RCS). The beam injection is one of the most important issues for the CSNS accelerator complex. In this paper, the injection methods have been comprehensively studied, including phase space painting and H- stripping. By using the design scheme of the anti-correlated painting, the beam power has successfully reached 50 kW. However, some difficulties have been found in the higher power beam commissioning. In order to solve these key problems, flexibility in the CSNS design has been exploited to implement the correlated painting by using the rising current curve of the pulse power supply. The effectiveness of the new method has been verified in the simulation and beam commissioning. By using the new method, the beam power on the target has successfully risen to the design value. Secondly, according to the CSNS beam commissioning experience, based on the present design of the injection system, a new idea is proposed to perform both correlated and anti-correlated painting in the CSNS. By adopting an additional vertical shift bump generated by four additional alternating current (AC) magnets in the injection region, the local orbit can be manipulated to meet the requirement of correlated painting. The new method can not only perform the correlated painting, but also optimize the anti-correlated painting. The simulation study shows that the new method works well, and both correlated and anti-correlated painting methods are well performed.

Development of μSR apparatuses for a pulsed muon source at China Spallation Neutron Source

Muon spin rotation/relaxation/resonance (μSR) spectroscopy uses highly polarized muons to study the microscopic magnetic structure and dynamics of condensed matter. In addition to the five existing muon facilities, the first Chinese muon source, the Muon station for sciEnce technoLOgy and inDustrY (MELODY), is planned to be constructed in Phase II of the China Spallation Neutron Source (CSNS). It aims to provide intense and pulsed muon beams to conduct μSR applications in multiple disciplines. The group from the University of Science and Technology of China (USTC) participated in the collaboration with the CSNS accelerator group for the construction of the muon source. The USTC group led the research and development (R&D) of the first-generation photomultiplier tube (PMT)-based μSR spectrometer, and the design of the second-generation silicon photomultiplier (SiPM)-based spectrometer. The PMT-based spectrometer is a 128-channel prototype to demonstrate and develop key detector and electronics technologies for the planned MELODY. After several iterative designs and updates of detectors and electronics, the spectrometer prototype achieved a 7-ns dead time, which can record more than 12 positrons per channel per pulse according to the ISIS running experience. Based on the technologies developed from the first-generation spectrometer, the second-generation spectrometer will use SiPMs to accommodate over 2500 detector units to make better use of muons in MELODY. The two generation developments of Chinese μSR spectrometers will greatly advance the construction of MELODY, and provide high-quality data for users to interpret material properties in the near future.

Prototype of an early warning system based on deep learning for the CSNS accelerator

To send out early warnings before some failures of the China Spallation Neutron Source (CSNS) accelerator, the feature models of the CSNS accelerator vacuums and drift tube linac (DTL) temperatures have been established based on deep learning, and a prototype of an early warning system has been developed. This prototype of an early warning system was built based on the experimental physics and industrial control system (EPICS) architecture, and it is mainly composed of three parts: training, recognition and information release. Python was adopted for program design and development, and functions such as training samples acquisition, deep learning networks design and training, online recognition and information release have been realized. The test results show that the accuracy of this prototype can reach 98.4% for the test set generated based on the historical data of the CSNS accelerator vacuums and DTL temperatures, and the anomalies of the CSNS accelerator vacuums and DTL temperatures can be recognized based on the real-time data, and the early warnings can be sent out, which proves its feasibility and effectiveness.

Beam commissioning and beam loss control for CSNS accelerators

The China Spallation Neutron Source (CSNS) accelerators consist of an 80 MeV H− linac and a 1.6 GeV proton rapid cycling synchrotron (RCS), which provides 1.6 GeV proton beam to the target at a repetition rate of 25 Hz. The beam commissioning of CSNS accelerators had been started since April 2017, and to the end of February 2020, the CSNS reached the design beam power of 100 kW. The most important issue in high-power beam commissioning is the beam loss control, as well as the control of induced activities, to meet the requirement of manual maintenance. A series of beam loss optimization work had been done to reduce the uncontrolled beam loss. Transverse and longitudinal matching in the MEBT was performed. For RCS commissioning, the orbit and lattice correction, the matching between the rf frequency and the dipole field, the tuning of the injection beam were performed. Many efforts have beam made to depress the effects of space charge and collective instability for beam loss control, such as injection optimization, longitudinal beam dynamics optimization, tune optimization. The beam commissioning procedure and results for CSNS accelerators are introduced in this paper.

Electronics of Time-of-Flight Measurement for Back-n at CSNS

Back-n is a white neutron experimental facility at China Spallation Neutron Source (CSNS). The time structure of the primary proton beam make it fully applicable to use TOF (time-of-flight) method for neutron energy measuring. We implement the electronics of TOF measurement on the general-purpose readout electronics designed for all of the seven detectors in Back-n. The electronics is based on PXIe (Peripheral Component Interconnect Express eXtensions for Instrumentation) platform, which is composed of FDM (Field Digitizer Modules), TCM (Trigger and Clock Module), and SCM (Signal Conditioning Module). T0 signal synchronous to the CSNS accelerator represents the neutron emission from the target. It is the start of time stamp. The trigger and clock module (TCM) receives, synchronizes and distributes the T0 signal to each FDM based on the PXIe backplane bus. Meantime, detector signals after being conditioned are fed into FDMs for waveform digitizing. First sample point of the signal is the stop of time stamp. According to the start, stop time stamp and the time of signal over threshold, the total TOF can be obtained. FPGA-based (Field Programmable Gate Array) TDC is implemented on TCM to accurately acquire the time interval between the asynchronous T0 signal and the global synchronous clock phase. There is also an FPGA-based TDC on FDM to accurately acquire the time interval between T0 arriving at FDM and the first sample point of the detector signal, the over threshold time of signal is obtained offline. This method for TOF measurement is efficient and not needed for additional modules. Test result shows the accuracy of TOF is sub-nanosecond and can meet the requirement for Back-n at CSNS.

The run management system for CSNS

The 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 designed proton beam power is 100 kW in Phase-I. The CSNS accelerator can operate in different beam modes and beam destinations, and for each beam destination, the beam power must be strictly restricted; meanwhile, the linac and the RCS may operate independently during the commissioning stage. To satisfy these operation requirements, the run management system (RMS) was designed and deployed for CSNS. The run management system, including a hardware layer and a software layer, operates on the top level of the global control system. RMS coordinates the machine protection system, personnel protection system, timing system and other systems, to set and publish the machine states and machine modes, to verify beam parameters and to permit the beam extraction from ion source. The RMS has been operating for more than one and half years and has played an important role during the commissioning and operation of CSNS facility. This paper will introduce the design and implementation of the RMS for CSNS.

The design and construction of CSNS drift tube linac

The China Spallation Neutron Source (CSNS) is an accelerator-based multidisciplinary user facility constructed in Dongguan, Guangdong, China. The injector of the CSNS accelerator consists of 4 conventional Alvarez DTL tanks, and it accelerates an H- beam from 3 MeV to 80 MeV. There is a series of accelerator physics and technology challenges in the DTL design and construction. The transverse focusing is arranged in a FFDD lattice utilizing a newly developed electromagnetic quadrupole magnets. The DTL cavity is copper-plated to enhance the electrical conductivity of the tank inner RF surface. There is not any space for steering magnet installing in the 36 m long DTL section, which leads to a rather high precision requirements for fabrication, installation and RF tuning. Benefited from the advanced fabrication technology and optimized tuning strategy, the CSNS DTL shows an excellent performance in the beam commissioning. The beam is successfully accelerated to 80 MeV with nearly 100% transmissions. The detailed physics and cavity design are described, construction and beam commissioning results are also shown.

Status of AC Magnets for CSNS RCS

China spallation neutron source accelerators include a 80-MeV Linac, 1.6-GeV rapid cycling synchrotron (RCS), and two beam transport lines. There are 24 direct current (dc)-biased 25-Hz alternating current (ac) dipole magnets, 48 dc-biased 25-Hz ac quadrupole magnets, 16 dc sextupole magnets, 34 ac correcting magnets, and 23 injection and extraction magnets for the RCS. In this paper, the status of RCS ac magnets will be presented and the key technical issues for the ac magnet performance, such as eddy current effect, high voltage, vibration, field nonlinearity, and fringe field interference will be thoroughly discussed.

Production target and muon collection studies for an experimental muon source at CSNS

Intense muon beams have very important applications by using μSR techniques and other methods. An experimental muon source (EMuS) as a parasitic facility at China Spallation Neutron Source (CSNS) is proposed. EMuS makes use of a small portion of the high power proton beam from the CSNS accelerator complex. It will provide an excellent platform for muon beam based multidisciplinary research, and will also serve as the development base for a future full-scale muon source at CSNS. The available proton beam power of 4kW at 1.6GeV can produce intense muon flux with a thick production target. The muon yields with different target materials and shapes, and the muon collection efficiency have been simulated by using the FLUKA code. It is found that the graphite target of about 10–12cm in thickness and rectangular in cross-section is a good choice, and that the collection at 90° from the beam direction is the best for surface muons. It is found that 4-D emittance volume instead of two independent 2-D emittances should be used to define the relation between the optimal muon intensity and the muon channel acceptance, due to the asymmetry between the distributions in the two transverse phase planes. The collected muon intensities for both surface muons and cloud muons with different emittances have also been studied, which are important for designing the muon beam transport line. The intensities of positive and negative muons are in the orders of 105μ+/s and 104μ−/s, respectively.

Design and experiment results of the LEBT pre-chopper for CSNS

In a high intensity proton accelerator complex comprising a linac and a ring, a beam chopper is often necessary in order to reduce the beam loss during injection from the linac to the ring. The China Spallation Neutron Source (CSNS) front end incorporates a pre-chopper in the Low Energy Beam Transport line (LEBT) that will remove a 530 ns section of beam at approximately 1 MHz rate. Physical design of the pre-chopper is presented in this paper. The distinguished feature of this electrostatic beam chopper is the novel design of deflecting structure, and the theoretic fast beam rise/fall time, which is an essential requirement for CSNS accelerator to avoid radioactivity induced by the lost particles due to insufficient chopping during the transient time; Taking advantage of the existing LEBT of the Accelerator Driven Subcritical System (ADS), the beam study of a similar chopper system was successfully performed and the achieved rise/fall time was less than 20 ns, which is the fastest one compared to other similar pre-choppers. This type of pre-chopper will be used in the CSNS LEBT, which is under construction.

Introduction to the overall physics design of CSNS accelerators

The China Spallation Neutron Source (CSNS) is an accelerator-based facility. The accelerator of CSNS consists of a low energy linac, a Rapid Cycling Synchrotron (RCS) and two beam transport lines. The overall physics design of CSNS accelerator is described, including the design principle, the choice of the main parameters and design of each part of accelerators. The key problems of the physics design, such as beam loss and control, are also discussed. The interface between the different parts of accelerator, as well as between accelerator and target, are introduced.

Characteristics and Potential Applications of the Proton Beams at the CSNS

The China Spallation Neutron Source (CSNS) is a large scientific research facility mainly serving the multidisciplinary research on material structure by using the neutron scattering technique. The accelerators can provide a proton beam of 120 kW with a repetition rate of 25 Hz, and can be upgraded to 240 kW (CSNS-II) or 500 kW (CSNS-IF). Besides as a driving source for the spallation target, the proton beams can be exploited for various applications both in fundamental research and in applications. The utilization of the CSNS proton beams can be in two different modes: the parasitic mode and the dedicated mode. The former one does not affect the normal operation of the spallation neutron source, and the latter can provide the full potential of the CSNS accelerators. Applications using the CSNS proton beams will be in two separate areas, utilizing the beams from the linac and from the RCS, respectively. Some of the CSNS proton beam applications are space single event effect and space radiology studies, white neutron source, proton therapy on ocular melanomas and low-depth cancers, fast neutron therapy, and borium capture neutron therapy. Other applications, such as testing studies of particle detectors, non-space radio-biological studies, radiation material studies, and nuclear physics, are also under consideration.