Physical Review Accelerators and Beams

Accurate modeling of positron sources is essential for next-generation high-luminosity lepton colliders. This study presents the first experimentally validated start-to-end simulation framework for positron production and capture, benchmarked against beam measurements at SuperKEKB, the world’s most intense positron source. Combining Geant4 with RF-Track, the model successfully reproduces measured positron yield and parameter scans. Additionally, detailed benchmarking was conducted with other simulation tools, including EGS5, GPT, and ASTRA. The work establishes a robust and reliable framework for designing and optimizing future high-intensity positron sources such as the FCC-ee.

Calculating Coherent Synchrotron Radiation (CSR) effects is one of the most computationally demanding tasks in accelerator physics. We address this using machine learning models—convolutional neural networks, including U-Nets, and a latent conditional diffusion model—trained on physics-based simulations of electron bunches in steady-state circular orbits. These models rapidly predict 3D CSR wakefields, achieving up to 1000× speedups, generalize well to varied distributions while maintaining reliable precision and efficiency for accelerator applications.

An implementation of a surface-impedance boundary condition in finite-difference time-domain electromagnetic codes making use of locally conformal (i.e. “partially filled”) cells for the modeling of finite-resistivity conducting surfaces is described. The model, which obviates the need for spatial resolution of the skin depth, is demonstrated by performing several test problems involving objects with finite conductivity in both relatively simple and more complex geometries.

This study presents a comprehensive investigation of intra-bunch dynamics in a high-intensity proton synchrotron, where strong space-charge forces and large chromatic phase coexist, through theoretical analysis, simulations, and experiments at the J-PARC Main Ring. Simulations supported by analytic foundations and experimental results, reveal how space charge modifies the decoherence and recoherence of intra-bunch motion, as well as the importance of indirect space-charge effects to suppress the beam instabilities. This integrated approach deepens the understanding of beam instabilities and provides a basis for future control strategies in MW-class proton drivers.

The FCC-ee injector complex requires a high-energy linac capable of accelerating beams to 20 GeV with excellent stability and efficiency. We present a comprehensive RF design and optimization of traveling-wave structures operating at 2.8 GHz, including beam-loading compensation, wakefield suppression, and pulse compression. The resulting design achieves high power efficiency, minimal energy spread, and robust thermal-mechanical stability, providing a reliable foundation for the FCC-ee injector.

In laser wakefield accelerators, pulse-front tilt in a driving laser pulse can deviate both the laser and the electron beam. Here, we examine experimentally how this steering applies to the x-rays generated during acceleration. The correlation with the electron deflection is determined, enabling non-invasive active stabilization of either beam, without significant impact on key beam parameters such as energy, charge, and divergence.

The work presents a new digital filter suitable for the construction of a single pick-up transverse feedback (TFB) with a larger tune acceptance and higher gain than can be achieved by the traditional Hilbert phase-shifter technique.

We propose methods to extract key parameters required for optimal feedback operation solely through active manipulations of the beam by the transverse feedback system and analysis of data acquired from it. They allow not only to shorten the TFB commissioning time from several shifts to less than a minute, but also regular, fully automated TFB system checks which can now be performed in case of suboptimal performance, saving significant amounts of machine time.

Coherent wiggler radiation (CWR) can play a significant role in the collective dynamics of low-energy, high-current electron–positron colliders. This work develops analytical models to quantify CWR impedance and evaluate its impact on beam stability including its interplay with coherent synchrotron radiation (CSR) impedance. The results offer practical guidance for wiggler design and beam-stability optimization in new-generation tau–charm factories and other electron rings employing damping wigglers.

Very high energy electron (VHEE) beams have been explored as a radiotherapy modality offering advantageous dose distribution, deep penetration and potential of ultra-high dose-rate, but compact delivery from laser-wakefield accelerators (LWFAs) remains hindered by large energy spreads. This work proposes a simple scheme using only two dipole magnets to guide LWFA-based VHEE beams along varied trajectories, achieving a concentrated dose peak up to 20 cm deep in a water phantom while minimizing entrance dose. Robust to energy spreads and enabling precise control, the approach supports uniform dose profiles via weighted superpositions, paving the way for compact, clinical LWFA-VHEE systems.