Digital Low-Level RF control system for Advanced Light Source Storage Ring

TL;DR

This paper details the commissioning and performance of a digital Low Level RF control system for the Advanced Light Source storage ring, achieving high stability and fast interlock response since 2017.

Contribution

The paper introduces a novel digital LLRF system with synchronized channels, real-time diagnostics, and interlocks, supporting hybrid operation modes at 500MHz.

Findings

RF amplitude stability < 0.1%

Phase stability < 0.1 degree

Interlock latency < 2.5 microseconds

Abstract

We have commissioned the digital Low Level RF (LLRF) system for storage ring RF at Advanced Light Source at Lawrence Berkeley National Lab (LBNL). The system is composed of 42 synchronous sampling channels for feedback control, diagnostics, and interlocks. The closed loop RF amplitude and phase stability is measured as < 0.1% and < 0.1 degree respectively, and the real-time machine protection interlock latency is measured < 2.5 microsecond. We have also developed PLC-FPGA-EPICS interfaces to support system configurations between hybrid operation modes using two klystrons driving two RF cavities at 500MHz resonance frequency. The deployed LLRF system has been operating since March 2017.