Efficient positron injection in plasma wakefield acceleration is challenging because it requires a field structure that can both focus and accelerate positrons. Here, we propose a self-adaptive catch-up injection scheme, in which a positron source placed in front of a hollow, positively charged driver is naturally captured as the wake catches up. Analytical modeling and 3D PIC simulations show that positrons with broad initial conditions can be injected into similar accelerating phases and further accelerated to multi-GeV energies.These results provide a proof-of-principle demonstration for a new positron injection and acceleration scheme in plasma wakefields.

How much data does a machine really need to understand itself? For pulsed accelerator systems, the answer may be just one waveform. A kernel-based Dynamic Mode Decomposition framework exploits Takens’ delay embedding to learn complete system dynamics from a single reference pulse, constructing a physics-aligned ordinary differential equation surrogate using only 5–10% of the available phase-space states. Validated on five beam kicker and pulse-forming network (PFN) modulator systems at SSRL/SLAC across three years, the approach achieves sub-percent reconstruction error, outperforms conventional methods by up to 100 times, and detects hardware anomalies automatically.

Multipactor (MP) discharge is a major factor limiting the performance of superconducting RF cavities. We propose a novel scheme for MP suppression based on the controlled excitation of higher-order quadrupole modes in a superconducting spoke resonator. Analytical symmetry arguments and simulation studies show these quadrupole fields suppress MP while imparting zero net transverse kick and negligible emittance growth to the proton beam in the MEHIPA-II linac, over the energy range of 40 to 200 MeV. This flexible approach offers an effective alternative to control persistent electron activity, enabling more stable and uninterrupted operation of a high‑gradient SRF linac.

In the Hadron Storage Ring of the Electron-Ion Collider, preservation of helion polarization is especially challenging: a large anomalous magnetic moment and asymmetries in the magnetic optics drive a dense spectrum of strong spin resonances, unlike the more symmetric RHIC proton case. This work compares two snake-matching strategies, betatron phase optimization and Siberian-snake axis optimization, and finds a clear advantage for symmetry-based spin control. By introducing the Doubly Lee-Courant scheme, which enforces local $\pi$ spin phase advance across every consecutive snake pair, the study provides a robust foundation for high-polarization beams in the EIC and future facilities.

Conventional laser-driven proton acceleration suffers from a trade-off between maximum energy and conversion efficiency as the accelerating field and the ion bunch quickly lose synchronization. We overcome this by combining two laser pulses with a micronozzle structure. With precise timing control, the proton bunch remains phase-locked to the co-moving field, enabling sustained acceleration with far higher efficiency. Our simulations show that sub-GeV-class proton energies can be achieved with a total laser-to-proton conversion efficiency of approximately 20%. Over 13% of the laser energy is transferred to protons above 100 MeV, useful for applications such as neutron and muon sources.

We developed a waveguide-type RF window with a simple structure to seal the vacuum for the cavity at continuous-wave RF frequency (509 MHz) and power (up to 250 kW) in the electron storage ring. This RF window can be replaced on-site quickly in the event of a ceramic plate puncture during beam operations. Although the high-power RF operations faced issues with abnormal heating due to a high loss tangent and multipactor discharges on the ceramic plate, we developed effective countermeasures. These RF windows were finally installed in NanoTerasu, a light source facility in Sendai, Japan, and have been operated without any problems.

We study an electromagnetic field of a thin extended bunch of charged particles forming over some finite time. We show that the radiation field is the main part of the total field in the relatively thin spherical layer. The energy characteristics of the radiation are calculated and analyzed. The radiation under consideration is compared with the radiation of a point variable charge moving with a constant velocity, as well as with bremsstrahlung of a point charge having constant magnitude.

Fixed Field alternating gradient Accelerators (FFA) remove the need for a time varying magnetic field and enable highly intense beam pulses in a flexible time structure, limited only by the acceleration system. Beam stacking allows an FFA to accumulate beam and reach the space-charge limit at the extraction energy, making FFAs promising candidates for next-generation spallation neutron sources such as ISIS-II. However, RF knockout can cause significant beam loss during stacking. To make beam stacking viable in high-intensity FFAs, this loss must be mitigated. Here, we show that a symmetric arrangement of RF cavities cancels the RF knockout perturbation, enabling lossless beam stacking.

Coherent Transition Radiation Michelson Interferometry (CTRI) is a compact technique for measuring the temporal profiles of electron bunches, but accurate reconstruction of ultrashort electron bunch profiles is hindered by optical filtering and phase ambiguity. This work develops an imaging-based numerical frequency-filter model and a genetic-algorithm (GA) forward-fitting method to reconstruct bunch profiles directly from time-domain interferograms. The approach provides a practical framework for advanced electron bunch diagnostics in accelerator experiments.

To address the increasingly severe target damage of linear induction accelerators for flash radiography, this paper proposes a solution adopting an electromagnetically driven high-speed moving target. Preliminary physical design and verification experiments have been completed, which verify the feasibility of the proposed scheme. This method is expected to resolve the multi-pulse target issue of flash radiography accelerators.

High-current electron storage rings require efficient collimation to protect superconducting magnets and minimize detector backgrounds. We present the first baseline collimation system design for the Electron-Ion Collider electron ring, combining optimized lattice integration with multi-turn particle tracking simulations. The proposed system localizes beam losses and reduces interaction-region losses by up to two orders of magnitude while preserving machine acceptance and beam lifetime, establishing a robust foundation for future EIC operations.

This study demonstrates the significance of magnetic fields in vacuum arc initiation, which can be a major design limitation in numerous devices operating at high electric fields in vacuum. Most previous studies on vacuum arcing have neglected the magnetic field or used simplified theoretical models, while high magnetic fields have been demonstrated to contribute significantly to arc occurrence. Our study examines the electron emission and heating processes by simulation, which provides more accurate details on the processes involved. This benefits understanding of the phenomenon itself, as well as its influence on applications.

Medium-temperature (Mid-T) baking can significantly improve the quality factor of SRF cavities, reducing cryogenic losses and energy consumption. Conventionally, this treatment is performed in vacuum furnaces, introducing contamination risks and reoxidation of the niobium surface. We investigate an $in$ $situ$ approach in which a TESLA 9-cell cavity is heated directly by RF power via the TTF-III coupler in the fundamental passband. Combining experiments with a validated thermal model, we show that alternating modes can provide the temperature uniformity required for effective Mid-T baking, enabling furnace-free $in$ $situ$ processing of SRF cavities within accelerator modules.

Understanding photoemission from electron sources in typical accelerator environments requires an easily accessible diagnostic method that can probe the position and momentum of electrons at the moment of emission. We experimentally demonstrate a method that uses a beam phase space diagnostic to compute the transfer matrix of a beamline and reconstruct the source 4D transverse phase space of a spatially structured photocathode. This method can uncover local correlations that other diagnostics might miss and aid in particle source design.

In next-generation light sources, a key challenge common to off-axis injections based on both dipole kickers and nonlinear kickers still remains: mitigating the field distortion caused by eddy currents in the metallic coating of the ceramic vacuum chamber, while minimizing beam coupling impedance and induced heating. We prototyped a chamber with a strip-patterned titanium coating on its inner surface tailored to requirements of SPring-8-II and evaluated the eddy current effects.

Modern compact cyclotrons are generally equipped with spiral inflectors for axial injection of the beam. Until now, spiral inflectors have been electrostatic, which limits space charge neutralization of the beam, preventing higher beam currents from being achieved. A proposed solution has been to use a magnetic inflector, which has the added advantage of allowing higher energy injection due to the scaling of the magnetic force. Here we demonstrate the design, construction, and testing of the first proof-of-concept magnetic spiral inflector.

In storage rings, focusing perturbations break lattice periodicity and degrade nonlinear performance. We introduce asymmetry parameters from Fourier harmonics of beta functions and resonance driving terms to quantify this symmetry breaking. Compared to the commonly used beta-beat, these parameters show stronger relationships with dynamic aperture reduction, further enhanced when considering the frequency diffusion rate. The beta-beat serving as a reasonable indicator of dynamic aperture reduction is also physically explained based on the longitudinal variation of resonance driving terms.

Accelerating spin-polarized beams in circular accelerators is difficult because the beam’s polarization can be significantly reduced when its spin motion is in resonance with its orbital motion. For constant-speed resonance crossings, the corresponding depolarization can be estimated using the Froissart-Stora formula. However, higher-order resonances, which are the dominant depolarization mechanisms in colliders with Siberian snakes, typically involve a change in crossing speed at the moment of crossing. This work introduces an extension of the Froissart-Stora formula to this case with comparisons to numerical integration and tracking in the Relativistic Heavy Ion Collider.

Ultrafast science demands ultrashort electron beams, yet generating such high-brightness electron bunches remains challenging. In this paper we propose using tailored THz modulation within an undulator to sculpt MeV electrons into sub-femtosecond microbunch trains, achieving a few fs pulses with up to fC charge and tunable spacing. Downstream dispersion further compresses pulses, while upstream dispersion can engineer periodic comb-like structures with satellite features. This scheme may enable time-resolved structural probing and mark a step toward capturing real-time electron dynamics in matter.

High-luminosity electron–positron colliders require ampere-level beam currents, rendering coupled-bunch instabilities driven by RF-cavity accelerating modes a critical concern. For the Super Tau-Charm Facility, we demonstrate that these instabilities can be effectively suppressed over the full 1–3.5 GeV energy range using solely the baseline low-level RF (LLRF) proportional-integral (PI) loop. The combination of a unity proportional gain and half-revolution loop delay produces a notch-filter response that strongly attenuates the most dangerous odd modes. Analytical calculations, particle tracking, and Nyquist analysis collectively confirm the robustness of both beam and loop stability.