Precise measurements of the muon anomalous magnetic moment motivate the development of a low-emittance muon beam at J-PARC using rf linacs. Positive muons have so far been accelerated only through the radio-frequency quadrupole (RFQ) stage. We report the first full-size 324-MHz interdigital H-mode drift tube linac dedicated to muon acceleration. Designed to follow the RFQ and accelerate muons from 0.34 to 4.26 MeV, it uses a cost-effective three-piece copper cavity with monolithic drift tubes. Low-power tuning reduced the peak-to-peak on-axis field error to 1.4%. The cavity operated stably at the nominal peak power of 390 kW and reached an accelerating field 10% above the design value.

In the Z-pinch pulsed-power accelerators, multi-MA currents rapidly heat the electrodes above the threshold for plasma formation. The stability and dynamics of an electron sheath emitted from the highly magnetized electrode plasmas are investigated using semi-analytic theory and kinetic particle-in-cell simulation which show strong resistive plasma instability (RPI) growth. The nonlinear evolution of the RPI drives electron vortices and uncovers sufficient ion charge for plasma transport across the gap in several nanoseconds with plasma densities sufficient to generate published current losses via a Hall mechanism.

A new type of fast pulse generator which utilizes wideband RF amplifiers and a new chopper chamber with high-impedance strip-line electrodes has been developed to reliably and accurately cut out a short bunch from the long-pulsed beam emitted from a single-crystal CeB${}_6$ hot cathode at the X-ray free-electron laser (XFEL) facility SACLA. Using these apparatuses, we succeeded in forming a nanosecond multi-bunch structure in the thermionic electron beam and generating a double-bunch XFEL pulse with a total pulse energy of 1mJ at 10 keV. The results will provide new possibilities for XFEL beams: higher intensity, higher coherence, and higher pulse repetition rate.

This paper proposes a novel emittance compensation scheme for the HALF diffraction-limited storage ring based on the quantum excitation effect. The proposed quantum-excitation-based scheme achieves emittance compensation comparable to the usually used radiation-damping-based scheme, even though the compensation wiggler is significantly shorter. It also yields significantly smaller energy spread variations and thus very small effective emittance variations at dispersive straight sections, with the effective emittance considered basically compensated.

Coherent terahertz generation in storage rings is typically limited in repetition rate by the time required for radiation damping to restore the electron beam. We propose an active demodulation scheme that uses a phase-reversed laser interaction to rapidly compensate the induced energy modulation after THz emission. Simulations for HLS-II indicate that coherent 10-THz radiation could be generated at repetition rates on the order of 100 kHz.

Ultrashort electron beams from plasma accelerators enable a regime in which undulator radiation can be controlled on the scale of individual optical cycles. Simulations show that tailoring the undulator magnetic field can directly shape the emitted waveform, producing frequency-chirped pulses and cycle-to-cycle changes in polarization. This capability may open new opportunities for probing ultrafast dynamics and polarization-sensitive applications.

Laser modulation can improve the limited longitudinal coherence of modern storage rings, but most implementations use each region of an electron bunch only once per turn to generate coherent light. We propose multiple echo-enabled harmonic generation (multi-EEHG), which repeatedly uses the same region within one turn to deliver coherent light at different wavelengths to multiple beamlines. Simulations predict up to one billion photons per pulse with few-meV bandwidth without a monochromator. This approach makes more efficient use of stored electron bunches, enabling coherent light delivery to multiple experimental stations.

Sudden beam loss (SBL)—the loss of much of the stored beam within a few turns—has limited SuperKEKB’s luminosity for nearly five years, damaging collimators and the Belle II detector. Reproduction experiments and laboratory analysis pin SBL on dust–beam interactions. Such interactions occur at many accelerators, but SuperKEKB’s tiny vertical aperture (nano-beam scheme) and high stored current make the damage uniquely severe. One dust source was vacuum sealant degraded into black stains; removing them sharply reduced SBL. Yet because discharges also produce dust, SBL cannot be fully eliminated in high-current, nano-beam machines—a key lesson for future colliders like FCC-ee and CEPC.

Polarized electron beams are essential for precision measurements at future storage-ring colliders, but conventional self-polarization can take many hours. We model repeated interactions with intense laser pulses and embed the resulting spin and energy kicks in six-dimensional BMAD tracking of an FCC-ee Z-pole bunch. At a beam-preserving operating point, the simulated polarization reaches 0.69% after 100,000 turns with no macroparticle loss, identifying both the promise and practical laser requirements of multishot polarization.

A crabbing orbit is typically produced with crab cavities, but the same effect can arise through other mechanisms, including dispersion near an accelerating RF cavity or beam coupling impedance. We report the first experimental observation of crabbing induced by beam-beam interactions in the LHC. The measured displacement is approximately 10 m at one rms bunch length, in agreement with analytical predictions and numerical simulations. Wideband beam-position monitors resolve this signal, which is an order of magnitude smaller than the residual crabbing expected in the HL-LHC, validating a key diagnostic for future operation.

Laser Wakefield Acceleration offers the potential for more compact and cost-effective electron accelerators. Significant efforts are being made to improve electron beam quality for various applications, particularly through the design of suitable gas targets and optimization of laser and target parameters. The present study investigates LWFA in a specially designed capillary gas-cell setup for generating high-quality, GeV-scale electron beams using combined hydrodynamic and Particle-In-Cell (PIC) simulations. The results reveal the impact of tailored gas-density profiles on LWFA and beam quality, with multiple injection mechanisms identified and analyzed.

Scaling fixed-field alternating gradient (FFA) accelerators offer strong potential for high-intensity proton drivers but face complex nonlinear dynamics under tight spatial limits. Through large-sample tracking of over 360,000 configurations under engineering errors, a 300–600 MeV scaling-FFA lattice is established for the CSNS Phase-II upgrade. A spiral FD doublet lattice (N=16) is identified as the optimal baseline, mitigating parameter bottlenecks and expanding dynamic aperture. Machine learning feature attribution further reveals the critical role of vertical edge focusing in beam survivability.

We have demonstrated a new 11.424 GHz SLED-type RF pulse compressor capable of powering high-gradient X-band devices with pulse lengths around 20 ns. Our compact pulse compressor uses spherical cavities supporting axially symmetric TE modes with minimal electric fields on cavity surfaces, intended to improve high-power robustness versus existing compact spherical SLEDs using a TE dipole mode. Built and high-power tested at SLAC, it demonstrated a peak power of 317 MW over a FWHM of 27.1 ns. This is the highest peak power achieved from a single-stage compact SLED RF pulse compressor at this frequency, providing a viable route to the high-gradient, short pulse regime for RF accelerating structures.

Quantifying the ion fraction of mixed helium-carbon ion beams is essential for developing such beams for online range monitoring in ion beam therapy. Until now, it could only be obtained from invasive measurements after extraction. We introduce a novel noninvasive method that infers the mixing ratio directly in the synchrotron from RF regulation loop corrections caused by small rigidity offsets between the two ion species. Validated by simulations and measurements, it has become an established diagnostic tool for mixed-beam accelerator and medical physics research and could support the clinical translation of mixed-ion beam therapy by providing a basis for a mixing-ratio interlock system.

High-energy accelerator facilities require efficient beam interception without sacrificing experimental uptime or floor space. This study presents a compact, wall-embedded switchable beam dump that integrates both beam-pass and full-interception states inside a single vacuum vessel to enable fast operational switching. By synchronously rotating dynamic shielding units by 90°, the system isolates the beam upstream while providing safe personnel access to downstream experimental areas. Radiation-transport and vacuum simulations demonstrate compliance with stringent safety criteria, offering a scalable design to enhance operational flexibility in complex beamlines.

We propose a versatile electron-optical system featuring a semi-immersed electron gun and a magnetic coil that generates a nonadiabatic magnetic field for an electron-beam ion source (EBIS). The system is capable of producing electron beams over a wide operating range, with beam currents of 0.2–3.0 A, current densities of 200–1900 A/cm², and electron energies of 2–20 keV. This flexible design is ideally suited for carbon-ion cancer therapy accelerator facilities, charge breeding of radioactive ions, and other accelerator systems requiring highly charged ions.

The storage ring proton Electric Dipole Moment (sr-pEDM) experiment uses a novel symmetric-hybrid frozen-spin storage ring with radial electric bending and alternate magnetic focusing to minimize systematics, enabling precise measurement of the vertical rotation of the polarization of polarized stored proton beams. We present a detailed analysis of second-order effects arising from the interplay of stray radial magnetic fields with electric quadrupole and sextupole fields, and show how the ring’s symmetries—beam reversal and magnetic quadrupole polarity switching—suppress these effects below the sr-pEDM experiment’s targeted sensitivity.

We present a more accurate formula for calculating the intra-beam scattering (IBS)-induced path length deviation of an electron beam traversing the lattice, which can aid in lattice optimization. Additionally, we have developed a tool to simulate IBS-kick effects on beam dynamics. The tool can directly compute the IBS equilibrium emittance in storage rings and efficiently evaluate the associated path length deviations for an electron beam traversing a lattice. These capabilities are important for applications such as optical stochastic cooling and steady-state microbunching, which strictly require the isochronicity of lattice.

Extending electron cooling to very high energies can benefit significantly from redistribution of cooling between longitudinal and transverse degrees of freedom. Existing analytical treatments generally rely on a linear, small-amplitude approximation to the friction force, limiting their applicability to realistic cooler designs. We derive exact closed-form cooling rates with dispersive redistribution, expressed through Carlson elliptic integrals and reduced to elementary functions for a key special case. The results enable rapid and accurate optimization of high-energy electron coolers.

This work presents a new method for estimating the threshold current related to beam breakup (BBU) instability, utilizing a physics-inspired neural network. The proposed approach is significant for the development of efficient future particle accelerators. A multi-layered bidirectional long short-term memory (BiLSTM) neural network is used to analyze how the geometrical tolerances affect the BBU threshold current. The findings indicate that a physically meaningful feature significantly influences the predictive performance and generalization of the proposed BiLSTM-based neural network model.