The Rapid Cycling Synchrotron (RCS) of the China Spallation Neutron Source (CSNS) is planned to upgrade its beam power from the current 100 kW to 500 kW in the CSNS-II phase. However, significant beam-intensity-dependent transverse instability has already been observed during routine 100 kW operation. As the beam power increases further, this instability is expected to become much stronger. To effectively suppress the coherent transverse oscillations induced by impedance wakefields and injection errors, a bunch-by-bunch transverse feedback system is essential. This paper evaluates the performance of the digital filter and the complete bunch-by-bunch feedback chain, from the front-end electronics through the power amplifier to the strip-line kicker. Feedback system simulations are performed to optimize key parameters, providing critical guidance for the design, commissioning, and future operation of the system.

Following the successful profile measurement of an 80 MeV negative hydrogen (H⁻) beam using a laser wire monitor at the China Spallation Neutron Source(CSNS), an emittance measurement system with a Low-Gain Avalanche Diode (LGAD) sensor has been developed and is currently under commissioning this year. This system utilizes the LGAD to reconstruct the spatial distribution of neutral hydrogen atoms (H0) generated through laser photodetachment. By combining this distribution with laser wire position, it enables complete phase-space reconstruction and accurate emittance measurement of the H⁻ beam. This paper focuses on the design and characterization of the LGAD-based H0 distribution measurement system, including H0 energy deposition simulation, LGAD sensor performance characterization, the design of a ceramic PCB readout board, and local signal response tests. The proposed system offers a promising non-interceptive, high-precision solution for negative hydrogen beam emittance measurement.

Diagonal-cut plane Beam Position Monitors (BPMs) are used to measure the transverse position of the proton beam in the Rapid Cycling Synchrotron (RCS) at the China Spallation Neutron Source (CSNS). Significant transverse beam position offsets were observed at several locations along the RCS. These offsets are potentially attributable to abrupt changes in the cross-section of the upstream and downstream vacuum ducts, BPM calibration constants determined at a single frequency on the calibration system, and limitations in the position calculation algorithm. To assess the impact of the sudden changes in beam duct aperture, numerical simulations were performed. Additionally, BPMs were recalibrated on a test bench to evaluate the influence of abrupt cross-sectional changes in the BPM and vacuum ducts on the observed offsets at different frequencies.

In the upgraded accelerator of the China Spallation Neutron Source Phase II (CSNS-II) project, several multi-channel beam diagnostic detectors are installed, including a Ionization Profile Monitor (IPM) for measuring the injection beam profile and a Multi-Wire Profile Monitor for measuring the target beam profile. In the China Spallation Neutron Source (CSNS), similar multi-channel detectors typically utilize multiple PXIe acquisition cards to construct a PXIe-based signal acquisition system, which suffers from high cost and limited flexibility. This paper presents an alternative signal readout solution using a multi-channel high-speed digitizer to replace the PXIe system. The digitizer incorporates built-in front-end amplification functionality, eliminating the need for separate analog electronics for signal amplification. With a maximum sampling rate of 125 MS/s, it fully meets the sampling requirements for the beam pulse width in the CSNS-II Rapid Cycling Synchrotron (RCS), which ranges from 500 ns to 80 ns. Moreover, the multi-channel signal acquisition system implemented with this digitizer offers high integration and reduced cost compared to the PXIe system, making it an ideal choice for beam diagnostics systems.

DC Current Transformers (DCCTs) are essential instruments for non-interceptive beam current measurement in particle accelerators. The zero-flux modulation principle demands exceptional symmetry between paired magnetic cores to achieve sub-$\mu$A offset stability. Conventional core matching based on static magnetic parameters provides only an engineering approximation, as it neglects the dynamic magnetization behavior under AC modulation. This paper presents a novel approach employing unsupervised machine learning techniques applied to 6 dynamic magnetic parameters ($\mu_\mathbf{a}$, $\delta$, $B_\mathbf{r}$, $B_\mathbf{m}$, $H_\mathbf{c}$, $H_\mathbf{m}$) measured at 50 kHz sinusoidal excitation for 19 Fe-based nanocrystalline cores. Principal Component Analysis (PCA) reduces the feature space while preserving $89.64\%$ of total variance. An adaptive multi-objective K-Means strategy successfully isolates anomalous specimens ($K=2$), while a density-based evaluation framework partitions the remaining operational cores into 5 highly homogeneous sub-groups. This two-tier matching scheme enables a physically rigorous core pairing that accounts for real-world dynamic magnetization and domain wall losses under actual DCCT operating conditions.

The power upgrade of the China Spallation Neutron Source Phase II (CSNS-II) requires the Rapid Cycling Synchrotron (RCS) BPM system to operate under an extreme 107 dB ultra-wide dynamic range (20 mV to 50 V) and high signal power. The primary design challenges are mitigating thermal drift, suppressing reflections from impedance mismatch, and enhancing low-energy SNR.This paper presents the preliminary design and performance validation of an analog front-end board, adapting successful solutions from facilities like J-PARC MR. The design integrates thin-film resistor attenuators with an impedance tuning network for improved stability and reflection control. Crucially, a hybrid fast/slow switching attenuation strategy is applied: millisecond-level slow switching handles macroscopic changes, while innovative nanosecond-level fast switching enables dynamic gain conditioning during acceleration, significantly boosting the system's SNR.Performance verification results (including attenuation and S21 characteristics) confirm the feasibility and core metrics of the circuit under high-power conditions, providing essential technical guidance for the final implementation at the CSNS-II RCS.

The analog electronics for the Beam Loss Monitoring (BLM) system in the superconducting section of CSNS II is mainly used for signal conditioning of the output signals from BLM beam loss detectors. For the BLM electronics of CSNS I, a single-channel transimpedance circuit was designed. The overall response time of the detector, transmission cable, and electronics is approximately 150 μs, with a focus on high-sensitivity design, which fails to meet the 10 μs response time requirement for machine protection in the superconducting section of CSNS II. Referring to the design of the LHC BLM electronics, a Charge-to-Frequency Conversion (CFC) circuit has been developed to split the charge generated by beam loss ionization into cumulative charge packets Qt with a fixed time interval T. Machine Protection System (MPS) triggers are generated by comparing the count from a counter with a calibrated unit-time count, and a high-speed ADC samples the frequency waveform to calculate the beam loss value through algorithms.

Two sets of Wall Current Monitors (WCMs) have been installed in the Rapid Cycling Synchrotron (RCS) of the China Spallation Neutron Source (CSNS) to fulfill three core beam diagnostic objectives: synchronous measurement of longitudinal bunch shapes across both macro and micro scales, accurate calculation of longitudinal emittance, and effective diagnosis of beam instabilities. This article focuses on the comprehensive discussion of the entire WCM system (probe and DAQ system) and its practical application during CSNS-RCS beam commissioning. The WCM system has performed quite well during the beam commissioning over the past years.

The China Spallation Neutron Source (CSNS) accelerator, consisting of a $\rm H^-$ linac and a rapid cycling synchrotron (RCS), is undergoing an upgrade to increase the average beam power to 500~kW. At the CSNS linac, shorted-stripline beam position monitor~(BPM) determines beam position by averaging over the entire macro-pulse. However, significant intra-macropulse beam position fluctuations have been observed in recent commissioning, which may cause undesired beam loss and degrade the injection efficiency. In this work, an intramacropulse beam position is reconstructed method based on the signal integral algorithm. During 2025 autumn and 2026 spring operation, the intra-macropulse beam position behaviors have been uncovered at the MEBT and LRBT sections. Although beam conditions vary between two different experiments, a significant beam position drift during the first~100~{$\mu$s}, with a maximum amplitude of more than 4 mm, has been revealed.

The Rapid Cycling Synchrotron (RCS) of the China Spallation Neutron Source (CSNS) is planned to upgrade its beam power from the current 100 kW to 500 kW in the CSNS-II phase. However, significant beam-intensity-dependent transverse instability has already been observed during routine 100 kW operation. As the beam power increases further, this instability is expected to become much stronger. To effectively suppress the coherent transverse oscillations induced by impedance wakefields and injection errors, a bunch-by-bunch transverse feedback system is essential. This paper evaluates the performance of the digital filter and the complete bunch-by-bunch feedback chain, from the front-end electronics through the power amplifier to the strip-line kicker. Feedback system simulations are performed to optimize key parameters, providing critical guidance for the design, commissioning, and future operation of the system.

Achieving sustainable beam operation in high-power accelerators requires careful control and minimization of halo-particle-induced beam loss. To accomplish this, it is important to have a clear understanding of the halo-particle distribution. While state-of-the-art instruments can achieve a dynamic range of ~10^6 with counting readout schemes, a novel fluorescence wire scanner combined with a conventional metal wire has recently been proposed and demonstrated at CSNS. This new approach has achieved a sensitivity at the single-particle level and a dynamic range of over 10^8. A 100x1x0.15 mm^3 fluorescence wire has been prepared, which has demonstrated excellent light yield and radiation hardness. By capturing fluorescence images with a general CMOS camera in a dark environment, a new record dynamic range of more than 10^8 has been achieved. Continue efforts on optimizing the fluorescence wire, observation system, and sensor hold promise for further improvements in dynamic range and sensitivity.