arXiv subjects

Hiroshi Kaji

Publications and source records attributed to Hiroshi Kaji.

4 recordsLinked to original sources

arXiv2026

KEK Accelerator Test Facility Low-Level RF and Timing Systems

The KEK Accelerator Test Facility (ATF) is a dedicated testbed for nanobeam technologies in support of the International Linear Collider (ILC). Stable pulsed operation requires synchronization of the facility timing system with the Low-Level RF (LLRF) system. The timing system distributes trigger and gate signals to key subsystems, including the DAQ, klystrons, laser systems, pulsed kicker magnets, and interlocks. The LLRF system provides phase-coherent RF references and facility-wide clock distribution for synchronization. Achieving ~100 fs-level synchronization depends critically on the phase-noise power spectral density (PN-PSD) of the distributed clock signals and on preserving this performance throughout the distribution network. We present facility-wide measurements of the KEK ATF LLRF clock PN-PSD and discuss the resulting synchronization floor imposed by the stability of the ATF Linac and Damping Ring signal generators.

physics.acc-ph↗

arXiv2025

Study of laser-beam arrival time synchronization towards sub-picosecond stability level

A precise synchronization between laser pulse and electron beam arrival time is essential for achieving sub-picosecond stability in modern accelerator facilities. In this work, a Low-Level RF system architecture combined with White Rabbit based timing system has been tested through a collaboration between KEK (Japan) and CNRS/IN2P3, IJClab (France). The setup combines a frequency standard generator, an IDROGEN carrier board with an embedded White Rabbit node, and SkyWorks synthesizers of different form factors to distribute phase-locked clock signals over telecommunication fiber. Phase noise power spectral density measurements were performed at several RF sub-harmonics to confirm synchronization performance. These results demonstrate the feasibility of implementing the White Rabbit-IDROGEN synchronization scheme for large-scale accelerators, including applications to laser-based diagnostics.

physics.acc-ph↗

arXiv2024

Development and Implementation of Advanced Beam Diagnostic and Abort Systems in SuperKEKB

The SuperKEKB/Belle II experiment aims to collect high-statistics data of B meson pairs to explore new physics beyond the Standard Model (SM). SuperKEKB, an upgraded version of the KEKB accelerator, has achieved a world-record luminosity of $4.71 \times 10^{34} \, \mathrm{cm^{-2}s^{-1}}$ in 2022 but continues to strive for higher luminosities. One of the major obstacles is Sudden Beam Loss (SBL) events, which cause substantial beam losses and damage to the Belle~II detector. To find a hint for addressing SBL challenges, advanced beam diagnostic systems and enhanced beam abort systems have been developed. The diagnostic system aims to accurately pinpoint the start of beam losses, while the upgraded abort system quickly disposes of anomalous beams to minimize damage. This paper details the development and implementation of these systems, including high-speed loss monitors, time synchronization with the White Rabbit system, and data acquisition systems. Efforts to understand the mechanisms of SBL events, using acoustic sensors to detect discharges, are also discussed. These measures aim to improve the operational stability and luminosity of SuperKEKB, contributing to the experiment's success.

hep-ex↗

arXiv2021

Analysis and Stabilization of AC Line Synchronized Timing System for SuperKEKB

A timing system provides high-precision signals to allow the controls over a variety of hardware and software components in the accelerator complex. This is guaranteed by the radio frequency (RF) and trigger signal synchronization for subsystems such as klystrons, pulsed magnets, and beam monitors. The main trigger signal should be distributed throughout the facility and repeated at the beam repetition rate. This trigger signal is usually generated by the same phase of an AC power line to follow the source of the fluctuation of an electrical grid and reduce the unwanted variation of the beam quality. To fulfill the needs of the multi-accelerator facility at KEK, apart from the normal trigger synchronization and bucket selection injection control, a beam operation scheme called the pulse-to-pulse modulation is utilized; hence, the complexity of the timing system increases. Uncertainty in the system and a trigger signal delivery error caused by a drastic AC power line drift are observed. Further, the effort to establish a reliable timing system at KEK and several solutions to improve the system robustness are presented.

physics.acc-ph↗