The dynamic enhancement of symmetry-breaking effects in neutron-nucleus resonances provides a sensitive testing ground for Time-Reversal Invariance Violation (TRIV). Exploiting this mechanism, the Neutron Optics Parity and Time Reversal Experiment (NOPTREX) seeks to elucidate the origin of the universe’s baryon asymmetry. Critical to this effort is the precise measurement of Parity Violation (PV) asymmetries, which is essential to calibrate the nuclear parameters required for future TRIV experiments. To facilitate these studies, we developed an eV polarized neutron at the Back-n white neutron beamline of the China Spallation Neutron Source (CSNS). Neutron polarization is generated by an in-situ Spin-Exchange Optical Pumping (SEOP) 3He filter. Spin manipulation is performed by an adiabatic spin flipper, while spin polarization is preserved over the flight path by a vacuum transport system equipped with a solenoidal guide field. Experiments successfully measured an asymmetry of approximately 7.8

To enhance the reliability and availability of superconducting radio-frequency (SRF) linear accelerators (LINACs), this study proposes and validates a novel global compensation-rematch method for fault recovery. The proposed method prioritizes the smooth evolution of the longitudinal phase advance per meter as the core physical constraint. By enforcing this constraint and redistributing the lost accelerating voltage among operational cavities, the method aims to simultaneously restore the nominal beam energy and preserve its quality. Its effectiveness is demonstrated through comprehensive beam dynamics studies and beam experiments on a low-energy, high-intensity proton LINAC, including multiparticle simulations using TraceWin software. Multiparticle simulations indicate that the normalized root-mean-square emittance growth is negligible after compensating for a 50

Recent investigations suggest that in a fourth-generation light source, where both fundamental-frequency and harmonic RF cavities are commonly used for bunch lengthening, variations in radiation energy loss per turn ( U_0 ) could cause a significant variation in bunch length. It is therefore necessary to compensate for the U_0 variations caused by changes in the gaps of the insertion devices (IDs). In this paper, we investigate a scheme based on two horizontal or two vertical damping wigglers to simultaneously compensate for horizontal emittance and U_0 variations induced by IDs. A theoretical analysis and an application example are presented.

Understanding the evolution of transverse beam profiles in high-intensity proton synchrotrons is crucial for stable, high-power operation. A residual gas ionization profile monitor (IPM) has been developed and commissioned for the Rapid Cycling Synchrotron (RCS) at the China Spallation Neutron Source (CSNS) to enable non-invasive, bunch-by-bunch horizontal beam profile measurements. During commissioning, key challenges such as electromagnetic interference (EMI) from the high-intensity proton beam and accelerator components, insufficient microchannel plate (MCP) gain due to power supply limitations, and elevated vacuum pressure were addressed through RF shielding and an enhanced Faraday cage for EMI suppression, a pull-down resistor for optimal MCP gain, and an additional vacuum pump for pressure reduction. These improvements enabled successful commissioning, with a peak-finding algorithm and RF-synchronized window technique developed to identify individual bunches and reconstruct profiles. Measurements were performed in both ion and electron collection modes, revealing beam position and horizontal size distributions during the injection painting process. This paper details the IPM’s design, commissioning strategies, and data analysis methods for achieving bunch-by-bunch non-invasive beam profile observations.

China Spallation Neutron Source phase-II (CSNS-II) upgrade project will build the first Muon Source MELODY (Muon station for sicEnce, technoLOgy and inDustrY) in China based on the high power proton accelerator. During the first stage, a muon target station and a surface muon beam-line will be constructed before 2029. The surface muon beam-line will focus on the applications of muon spin μSR spectroscopy. At the target station, muons are generated by proton pulses hitting the muon target and captured by a large aperture solenoid. However, a lot of positrons are also generated along with muons. These positrons have the same momentum as the muons and can be transport along the beam line. These positrons must be eliminated otherwise they will arrive at the spectrometer and disturb the signals induced by the interaction between the muons beam and the experimental samples. Wien filter is the key device in the beam-line to remove the positrons from the muon beam. A Wien filter consists of a dipole magnet and a high voltage electrostatic separator and can simultaneously generate the magnetic field and electric field perpendicularly to each other. Muons with velocity that equals to the ratio of the electric filed to the magnetic field ([Formula: see text]) can pass through the Wien filter without deflection. Meanwhile, positrons move much faster than muons resulting in a significant deflection. The optimization of the Wien filter structure can improve the field quality to make the E/B as constant as possible along the beam path and thus minimize the deflections to muons. This paper introduces the design details of a Wien filter at MELODY.

This study investigates the performance of a new compact (55 cm x 56 cm x 48 cm) in situ spin-exchange optical pumping 3He neutron spin filter (NSF) system developed at the China Spallation Neutron Source. The enclosed NSF cell, filled with 3He at 2.53 bar, achieved an initial 3He polarization of approximately 60%. After subsequent improvements in the magnetic field and heating system, this in situ system achieved a 3He polarization of 75.66%+/- 0.09%, resulting in 96.30% neutron polarization at 2 & Aring;. This highly compact in situ system is equipped with self-supportive features, pre-pumping capabilities, polarization maintenance, and a low-noise nuclear magnetic resonance system. These advantages significantly reduce the preparation time and simplify polarized neutron experiments, making it suitable for various neutron beamlines in China, particularly those with a limited sample space. These characteristics establish it as a quasi-standardized system that plays a vital role in polarized neutron experiments, including those involving polarized neutron imaging, neutron reflection, the performance calibration of polarized neutron instruments, and the neutron optics parity and time reversal experiment.

The rapid cycling synchrotron (RCS) at the China spallation neutron source operates as a high-intensity proton accelerator. The coupled bunch instability was observed during RCS beam commissioning, which significantly limited the beam power. To investigate the dynamics of instability under an increased beam power, a pulsed octupole magnet with a gradient of 900 T/m^3 was developed. The magnet system integrated an octupole magnet with a pulsed power supply. The field was carefully measured to examine the performance before its installation into the tunnel. After the installation of the magnets, beam measurements were performed to confirm the effectiveness of the instability mitigation on an actual proton beam. The measurement results show that the instability can be suppressed using the pulsed octupole magnet, particularly at the high-energy stage in an acceleration cycle, meeting the requirements for stable operation of the accelerator. Additionally, when the instability is completely suppressed through chromaticity optimization, octupole magnets can significantly enhance the RCS transmission efficiency, which is crucial for controlling beam loss. The pulsed octupole magnet offers significant progress in beam stability in the RCS, providing valuable experience for further beam power enhancement.

The focusing of pulsed neutrons can increase neutron current, reduce sample volume and enable access to smaller scattering angles. Consequently, it represents a critical challenge for next-generation spallation neutron sources. The primary difficulty stems from the inherent chromatic aberration of white neutrons. Here, a new compact nested rotating sextupole permanent magnet (Nest-Rotating-SPM) lens, with a total length of 200 mm, was developed and tested on the very small angle neutron scattering instrument at the China Spallation Neutron Source. Through synchronization of the outer sextupole lens rotation with the neutron pulse from the source, we achieved aberration-free focusing of neutrons with wavelengths between 11.0 and 15.5 angstrom for the first time. The implementation of water cooling and carbon fibre winding ensures both magnetic field stability and mechanical robustness of the inner sextupole. The compact design incorporating bridge sextupoles enables modular assembly of multiple lens units for focusing pulsed neutrons with wavelengths shorter than 10.0 angstrom, making it practically useful in a pulsed neutron instrument to enhance neutron current or access lower scattering vectors. Additional research is required to mitigate background noise.

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.

The design goal of 100 kW beam power of the China Spallation Neutron Source (CSNS) has been successfully achieved in 2020. In order to further increase the beam power more than 100 kW, a total of 16 programmable trim quadrupoles have been installed in the Rapid Cycling Synchrotron (RCS) of CSNS, to achieve accurate adjustment of betatron tunes, better control of twiss parameters, and restoration of lattice super -periodicity. In this paper, we describe the design and several important applications of the trim quadrupoles for beam commissioning in the CSNS RCS. The beam experiments show that the trim quadrupoles play a crucial role in increasing beam power above 100 kW.

An R&D project aiming to develop superconducting undulators (SCUs) is in progress at the Institute of High Energy Physics (IHEP) in China. The insertion device group has produced a 1.5-m-long NbTi planar superconducting undulator prototype recently. This SCU prototype has a period length of 15 mm and a magnetic gap of 9.5 mm. The SCU was fabricated in a frame to be trained vertically in a Dewar submerged by liquid helium. After dozens of quenches, the maximum current in the superconducting coils reached 450 A. The magnetic field along the axis at different currents were obtained by a measurement system to characterize the local magnetic field distribution. We applied a gap adjustment method to improve the magnetic field quality. A cryostat has been specially designed for this 1.5-m-long SCU prototype. The SCU was installed in the cryostat to be cooled to 4.2 K successfully. A series of cryogenic tests for the SCU prototype in the cryostat are in progress.

A Muon station for sciEnce, technoLOgy and inDustrY (MELODY) has been listed in the China Spallation Neutron Source upgrade plan, and the infrastructure construction is scheduled to start by the end of 2022. The 1:6 GeV double-pulsed proton bunch will be extracted from the Rapid Cycling Synchrotron (RCS) ring to a stand-alone target station. One surface muon and one decay muon beamline are designed to provide multi-terminals for applications. In this report, we describe the design of MELODY and prospect for future applications.

A pulsed muon facility (the so‐called EMuS) at the China Spallation Neutron Source (CSNS) has been studied since 2007. It aims for multidisciplinary applications but with a focus on those based on muon spin rotation/relaxation/resonance techniques. As a standalone facility, EMuS will take about 5% or 25 kW of the total beam power (500 kW) from the CSNS‐II accelerator complex. Two schemes have been designed: the baseline scheme is based on an inner conical target in graphite and superconducting solenoids for the capture and transport of pions and muons; the simplified scheme is based on a conventional thick target and room‐temperature magnets for transport. With the former, multiple kinds of muon beams can be provided, from surface muons, decay muons, negative muons, to low‐energy muons. Mainly surface muons are available with the simplified scheme. With a number of novel design concepts such as forward capture of pions/muons from a target station based on superconducting solenoids and triple spatial beam splitting of a muon beam, the design aspects of EMuS are presented here. The wide application potential and the R&D progress are also included.

The China Spallation Neutron Source incorporates a rapid cycling synchrotron (RCS) that operates by accumulating protons at 80 MeV and subsequently accelerating them to 1.6 GeV within a time span of 20 ms. The beam is guided to striking the tungsten target for neutron source. As a space charge dominated machine, the RCS is subject to space charge effects and momentum spread, hereby influencing the tune spread. To address this issue, sextupole magnets, powered by two families of DC power supply, were initially employed to decrease the absolute value of chromaticity and to control the tune spread. The head-tail instability has been observed during the RCS beam commissioning. The beam tests and simulations were conducted, revealing that tuning the chromaticity proved to be an effective mitigation strategy. However, to achieve better control over the tune spread and further suppress the instability, the DC sextupole field has been upgraded to an AC sextupole field, aiming to provide dynamic for controlling the chromaticity over an acceleration cycle. Thanks to the upgraded of AC field, the instability has been fully mitigated with beam power of 100 kW and the transmission in the RCS has been improved by 2

A compact nested rotate sextupole permanent magnet (Nest-Rot-SPM) lens was designed for the focusing of pulsed neutrons. It is based on the working conditions of the Very Small Angle Neutron Scattering (VSANS) instrument at the China Spallation Neutron Source (CSNS), and is expected to focus a neutron pulse from 6 Å to 10.5 Å, without chromatic aberration. Three hurdles must be addressed, i.e., the tremendous torque, the heat deposition, and the synchronization with the neutron pulse, respectively. The bore diameter and segment length of the lens are optimized using a formula analysis of the key parameters and model simulations of the torque and heat deposition. A twin torque canceling design is used to reduce the torque to one-third of its original value, or even lower. The goal of this project is to take the device into practical use in the VSANS at the CSNS.

Purpose The high energy photon source (HEPS) is a diffraction-limited storage ring light source being built in Beijing, China. The HEPS accelerators consist of the storage ring and its injector which includes the linac, booster and beam transport lines. The magnet system is one of the most important systems for the accelerators. In this paper, the field design, mechanical design and some special issues of the main magnets for the injector are presented. Methods The magnets for the linac and transport lines work at DC mode, whereas the magnets for the booster work at dynamic mode. So the module of OPERA/TOSCA is used to design the DC magnetic field and the module of OPERA/ELLEKTRA is used to design the dynamic magnetic field. The CAD programs are used to design the mechanical structures of the magnets. Results The magnetic field simulation results of all the magnets for the injector can meet the physical requirements, the mechanical designs of all magnets are reasonable, and engineering drawings of the magnets for production are finished. Conclusions Both the magnetic field design and mechanical design of all magnets are satisfied with the physical requirements of the HEPS injector; the production of all magnets has been started up.

In September 2018, China Spallation Neutron Source (CSNS) passed the national acceptance and started stable operation. Many scientific achievements have been made, but more and more experiments require accelerators with higher beam quality. Based on the current lattice layout and further research, an alternative upgrade plan is proposed for the CSNS, i.e., CSNS-II. The trim quadrupole magnet and the AC sextupole magnet are necessary. Both types of magnets with the number of 16 are respectively powered by the AC power supply and they were developed firstly in 2021. This article introduces dynamic magnetic field simulation, fringe field interference analysis, and DC/AC magnetic field measurements of the two types of magnets.

陶瓷真空盒作为中国散裂中子源(CSNS)快循环同步加速器(RCS)真空系统的关键部件,能避免RCS二极、四极交流磁铁因快速变化的磁场而产生的涡旋电流.因安装空间限制,RCS陶瓷真空盒支架固定在磁铁线圈上.在CSNS/RCS交流磁铁长时间加电测试中,出现陶瓷真空盒断裂、真空破坏的情况.为避免后期出现类似问题,从磁铁发热进而引起陶瓷真空盒不均匀升温的角度出发,对陶瓷真空盒的热特性进行了分析,同时基于双目视觉测量技术,对陶瓷真空盒的振动情况进行了监测,针对部分真空盒水平方向振动异常的问题,确定其影响因素为快卸链条的磁导率超标.最后开展了陶瓷真空盒的支架减振技术研究.

Accelerator magnet is one of the most difficult equipment in accelerator hardware system. With the improvement of physical requirements, more and more high technical requirements are put forward for magnets. This paper mainly introduces the new application of three coordinate measurement technology in the detection of accelerator magnet, and introduces the working process of CMM in the detection of accelerator magnet polar profile.

CSNS will build a muon source at the end of the RTBT. In the current design, the muon source proposes two schemes, namely the baseline scheme and the baby scheme. High voltage electrostatic deflectors (ESD) are used to deflect the beam in the two schemes. A three-channel ESD with 400 kV HV is employed in the baseline scheme and a 210 kV dual-channel ESD in the simplified scheme. According to physical requirements, the electric field concentration factor is introduced, and the electrode of ESD is theoretically designed 2D and 3D simulations are carried out to analyze the characteristics of electric field distribution by OPERA. The geometry of the electrodes also met the requirements of electric field uniformity, high voltage resistance and mechanical strength at the same time. In the baseline scheme and the baby scheme, the ESD electric field concentration factors are 1.36 and 1.53, and the maximum electric field is 6.78 MV/m and 4.6 MV/m, respectively. The design meets the requirements and is reasonably feasible. PHYSICAL CONSIDERATIONS The layout of CSNS and muon source is shown in Fig. 1. For μSR experiments, positrons are the main contaminations, and should be controlled below 5% on the sample. General eliminating methods include degraders followed by a dipole, or Wien Filters composed of cross electromagnetic fields. Today's muon sources prefer to use the latter due to the emittance increasement caused by the degrader. Because of the thick target of EMuS, the beam emittance in the beamlines is quite large and it’s difficult to focus onto a small sample required by typical μSR experiments. Even we can achieve this by collimation, however, the beam loss is much more than we expect. In addition, the direct application of Wien Filter to this beam with so large emittance results in extremely high requirements for a single Wien Filter, which will either increase the cost or bring more burden to operation and maintenance. As the repetition rate of CSNS proton accelerator is low, intensity is too high for the spectrometer if only one end-station is in use. So multiple end-stations are necessary. In view of characteristics above, we adopt a spatial splitting method based on arc-shaped electrostatic separators on EMuS, which not only removes positrons, but also allows simultaneous beam supply for multiple end-stations. After the electrostatic separator, a septum magnet is placed to further deflect beam to ensure sufficient space for layout. Since the phase space of muons and positrons in the septum magnet will be partially remixed, we must ensure that the phase spaces of muons and positrons at the exit of the electrostatic separator are separated enough. Figure 1: The layout of CSNS and muon source. For the baby scheme, limited by the layout, we plan to use a dual-channel electrostatic separator, with one channel straight and field-free, and the other channel located in a field area produced by arc-shaped electrodes. For the baseline scheme, we plan to design a three-channel electrostatic separator, with symmetrical arc-shaped electrodes on both sides, and a narrow field-free straight-through channel in the middle. The effective length of the deflection channels is constrained to 0.6-0.7 meter to guarantee the transmission rate. Also, the deflection angle is approximately 10-20 degrees so that polarization won’t be degraded too much. Follow the Eq. (1) below: L ρθ,E vB,Bρ , (1) we can estimate that the strength of electric field is around a few MV/m, and the specific value is given by g4beamline simulation. In the baby scheme, positrons are about 14 times more than muons. The effective length of the separator is set to 0.66 m. When the deflection angle reaches 15.6 degrees, phase spaces of muons and the positrons are separated well enough, as shown in Fig. 2. The total voltage is 210 kV. Figure 2: Phase spaces of muons and the positrons are separated by ESD in baby scheme. As for the baseline scheme, superconducting solenoids collects positrons about 60 times of muons. With 0.7 m long separator, and 25 degrees deflection angle, phase spaces can be effectively separated. But now the voltage ____________________________________________ † wuyw@ihep.ac.cn 12th Int. Particle Acc. Conf. IPAC2021, Campinas, SP, Brazil JACoW Publishing ISBN: 978-3-95450-214-1 ISSN: 2673-5490 doi:10.18429/JACoW-IPAC2021-TUPAB362 TUPAB362 C on te nt fr om th is w or k m ay be us ed un de rt he te rm s of th e C C B Y 3. 0 lic en ce (© 20 21 ). A ny di st ri bu tio n of th is w or k m us tm ai nt ai n at tr ib ut io n to th e au th or (s ), tit le of th e w or k, pu bl is he r, an d D O I 2360 MC7: Accelerator Technology T09 Room Temperature Magnets has reached 400 kV. Electrodes with such high voltage will bring huge challenge for operations. Considering the above, the technical parameters of ESD are shown in Table 1. Table 1: The Technical Parameters of ESD Scheme Baseline Baby quantity 1 1 deflection angle (deg) 25 15.6 field area gap (mm) 80 50 field-free gap/entrance (mm) 24 140 field-free gap/exit (mm) 322 electric field strength (MV/m) 5 3 voltage (kV) 400 210 effective length(m) 0.7 0.66 electrode width (mm) 300 200 power source 1 1 ELECTRODE DESIGN In order to prevent high voltage local breakdown of the electrode, it is necessary to optimize the electrode [1, 2]. The electric field concentration factor β is introduced, which is defined as the ratio of the maximum field strength to the field strength in the central area, shown in Eq. (2). Empirically, it is required that β < 2, and the smaller β, the better the stability of the electric field between electrodes. β (2) The maximum field intensity is concentrated at the end of the electrode. The larger the chamfer radius R, the smaller the maximum electric field intensity and the smaller the electric field concentration factor. The cross section at the entrance of three-channel ESD for baseline scheme is shown in Fig. 3. It is shown R1: 25 mm, R2: 12.5 mm, R3: 6.25 mm, R4: 6.25 mm, L: 300 mm, d: 80 mm, a: 0.1 mm, b: 24 mm. Figure 3: The cross section at the entrance of three-channel ESD. ELECTRIC FIELD SIMULATION ESD for Baseline Scheme A three-channel electrostatic separator is adopted in baseline scheme. OPERA was used to perform 2D simulation of ESD, where R = 25 mm, electric field gap = 80 mm, electrode voltage 400 kV, and electrode length 300 mm. The simulation results show that the central electric field is 5 MV/m, the maximum electric field is 7.03 MV/m, and β = 1.406. The 2D electric field line distribution, the electric field intensity cloud diagram of the electrode and the vertical electric field distribution are shown in Figs. 4 and 5, respectively. Figure 4: The 2D electric field line distribution and the electric field intensity cloud diagram of the electrode. Figure 5: Vertical electric field distribution On the basis of the 2D simulation results, a 3D simulation was performed, in which the entrance gap of the fieldfree zone was 24 mm, and the electric field gap was 80 mm. According to the simulation results, the maximum field strength at the electrode is 6.78 MV, which corresponds to β = 1.36. The 3D structure, the electric field line distribution diagram of the center section of the magnet, the electric field intensity cloud diagram, and the beam trajectory electric field distribution diagram are shown in Figs. 6, 7, and 8, respectively. Figure 6: 3D structure. Figure 7: The electric field line distribution diagram of the center section of the magnet and the electric field intensity distribution cloud diagram. 12th Int. Particle Acc. Conf. IPAC2021, Campinas, SP, Brazil JACoW Publishing ISBN: 978-3-95450-214-1 ISSN: 2673-5490 doi:10.18429/JACoW-IPAC2021-TUPAB362 MC7: Accelerator Technology T09 Room Temperature Magnets TUPAB362 2361 C on te nt fr om th is w or k m ay be us ed un de rt he te rm s of th e C C B Y 3. 0 lic en ce (© 20 21 ). A ny di st ri bu tio n of th is w or k m us tm ai nt ai n at tr ib ut io n to th e au th or (s ), tit le of th e w or k, pu bl is he r, an d D O I