A New Damper for Coupled-Bunch Instabilities caused by the accelerating mode at SuperKEKB

TL;DR

This paper introduces a newly developed damper designed to suppress coupled-bunch instabilities at SuperKEKB, demonstrating successful test results and simulations indicating its effectiveness in stabilizing beam oscillations.

Contribution

The paper presents a novel LCBI damper for SuperKEKB that operates independently of main LLRF control, with validated performance through bench tests and simulations.

Findings

Damper effectively suppresses targeted LCBI modes (-1, -2, -3).

Test bench measurements meet required specifications.

Simulations suggest additional dampers may be needed for optimal stability.

Abstract

SuperKEKB is an asymmetric electron-positron circular collider based on nano-beam scheme at interaction region and large beam current. Large beam current makes growth rates of longitudinal coupled-bunch instabilities (LCBI) large. Especially some lowest modes near accelerating frequency are serious. On the design parameter for SuperKEKB, $\mu$ = -1, -2, -3 mode of LCBI can be destabilized. We developed new LCBI damper to suppress newly arisen LCBI modes ($\mu$ = -1, -2, -3) in SuperKEKB. The new damper will be installed in Low Level RF control system. The new LCBI damper is independent of main LLRF control components. In the test bench measurement, our new LCBI damper has good performance and satisfied required specifications. For preparation of using LCBI damper, we produced the simulation of beam oscillation damped by RF feedback. The results of this simulation shows that we need more dampers than them we prepared. We report profile of new damper and results of test bench measurement and feedback simulation in this paper.