The LCLS-II Gun & Buncher LLRF Controller Upgrade

TL;DR

This paper describes the upgrade of the LCLS-II Gun & Buncher LLRF Controller, detailing its hardware, firmware, software, and current status to improve the stability and performance of the accelerator's injector system.

Contribution

It presents a comprehensive upgrade of the LCLS-II injector's LLRF control system, including new hardware, firmware, and software functionalities for enhanced performance.

Findings

Successful implementation of feedback and Self-Excited Loop control logic

Enhanced functionalities like live detune computation and active frequency tracking

Current status and future development plans of the system

Abstract

LCLS-II is currently in its commissioning phase at SLAC. It is an X-ray FEL driven by a CW superconducting LINAC. The beam injector plays a crucial role in the overall performance of the accelerator, and is critical to the final electron beam performance parameters. The LCLS-II injector comprises of a 185.7 MHz VHF copper gun cavity, and a 1.3 GHz two-cell L-band copper buncher cavity. The FPGA-based controller employs feedback and Self-Excited Loop logic in order to regulate the cavity fields. It also features several other functionalities, such as live detune computation, active frequency tracking, and waveform recording. The LLRF system drives the cavities via two 60 kW SSAs through two power couplers, and thus stabilizes the fields inside the plant. This paper provides an outline of the general functionalities of the system, alongside a description of its hardware, firmware and software architecture, before finalizing with the current status of the project and its future goals.