Recent developments in LLRF and its controls at CERN Linac4

TL;DR

This paper discusses recent improvements and control system developments for CERN's Linac4 RF system, including adaptive feed forward, set point modulation, and automation tools, to enhance performance and stability.

Contribution

It introduces new control features like adaptive feed forward and automation tools, addressing challenges from different RF station types at CERN's Linac4.

Findings

Adaptive feed forward shows promising results in stabilizing RF performance.

New control features improve stability and operational efficiency.

Automation tools facilitate setup and monitoring processes.

Abstract

At the end of the Large Hadron Collider's Run 2, CERN's Proton Injector Linac 2, commissioned in 1978, delivered its final beam in December 2018. For Run 3, from March 2021, a new H$^{-}$ will take over the role: Linac4. The machine has been producing test beams since 2013 and in 2016 it reached its design 160 MeV energy with 20 mA beam current. Since then several improvements have been made which enhance the LLRF performance and stability. In this paper the structure of the machine and the control system are presented. Problems arising from different RF station types are described and our solutions explained, along with new features recently added to the LLRF. An Adaptive Feed Forward implemented as a flexible hybrid hardware-software solution is described, and first results of this application running on a laboratory test stand are presented. Addition of the set point modulation needed for longitudinal phase-space painting is discussed. Finally, software tools for automation of setting up, monitoring and operations are described. As the hardware and low-level software are still reaching maturity, these are only briefly introduced here.