Longitudinal Mode-by-Mode Feedback System for The J-PARC Main Ring

TL;DR

This paper presents a new longitudinal mode-by-mode feedback system for the J-PARC Main Ring to suppress coupled-bunch instabilities at high beam intensities, enhancing beam stability for neutrino experiments.

Contribution

The paper introduces a FPGA-based feedback system with single sideband filtering to effectively detect and mitigate coupled-bunch oscillations in a high-power proton synchrotron.

Findings

The feedback system's frequency response matched simulations.

Oscillation amplitudes measured agreed with oscilloscope data.

System successfully mitigated instabilities at high beam power.

Abstract

The J-PARC Main Ring (MR) is a high intensity proton synchrotron, which accelerates protons from 3 GeV to 30 GeV. The MR delivers $2.6\times10^{14}$ protons per pulse, which corresponds to the beam power of 500 kW, to the neutrino experiment as of May 2018, and the studies to reach higher beam intensities are in progress. During studies, we observed the longitudinal dipole coupled-bunch instabilities in the MR for the beam power beyond 470 kW. To mitigate them for higher beam intensities, we have developed a longitudinal mode-by-mode feedback system. The feedback system consists of a wall current monitor, a FPGA-based feedback processor, RF power amplifiers, and a RF cavity as a longitudinal kicker. In the feedback processor, we utilize the single sideband filtering technique to detect the oscillation components of the individual coupled-bunch mode in the beam signal. The frequency response of the filters in the feedback processor matched well with the simulation. The oscillation amplitude of the coupled bunch oscillation measured by the system agreed with the oscilloscope analysis.