Design and performance of the LLRF control system for CSNS LINAC

TL;DR

This paper discusses the design and successful implementation of a digital low level RF control system for the CSNS linac, achieving high stability and precision in RF field control during beam operation.

Contribution

It presents a reliable digital LLRF control system design that meets and exceeds the stability and precision requirements for the CSNS linac.

Findings

Control precision met beam commissioning requirements

Amplitude and phase variations were within specified limits

System operated stably during beam commissioning

Abstract

The China spallation neutron source (CSNS) linac is designed with beam energy of 81MeV and a peak current of 15mA in the first phase. The RF power system for the 81 MeV Linac requires 8 units of RF power sources, each unit has one independent digital low level RF (LLRF) control system which is used to stabilize the amplitude and phase of the RF accelerating field along the linac, and to minimize beam loss. During beam commissioning, all of 8 on-line units of LLRF control system were operating stably and reliable, the control precision of accelerating fields met requirement of beam commissioning. The amplitude and phase variations of the linac fields are less than $\pm$0.2% and $\pm$0.2$^\circ$ without beam loading, or $\pm$0.5% and $\pm$0.5$^\circ$ with 10mA beam loading, much better than the design requirements of $\pm$1% in amplitude and $\pm$1$^\circ$ in phase.