LLRF System Analysis for the Fermilab PIP-II Superconducting LINAC

TL;DR

This paper analyzes the Low-Level Radio Frequency (LLRF) control system for Fermilab's PIP-II superconducting linac, focusing on design, testing, and operational limits to ensure precise cavity field regulation.

Contribution

It presents an analysis of the LLRF system architecture, control strategies, and testing results tailored for the high beam loading conditions of PIP-II.

Findings

Control system can meet regulation requirements under high beam loading

Self-excited loop architecture is effective for superconducting cavities

Operational limits of feedback gains are identified

Abstract

PIP-II is a superconducting linac that is in the initial acceleration chain for the Fermilab accelerator complex. The RF system consists of a warm front-end with an RFQ and buncher cavities along with 25 superconducting cryo-modules comprised of cavities with five different acceleration \(\beta\). The LLRF system for the linac has to provide field and resonance control for a total of 125 RF cavities. Various components of the LLRF system have been tested with and without beam at the PIP-II test stands. The LLRF system design is derived from the LCLS-II project with its self-excited loop architecture used in the majority of the cryo-modules. The PIP-II beam loading at 2 mA is much higher than the LCLS-II linac. The control system architecture is analyzed and evaluated for the operational limits of feedback gains and their ability to meet the project regulation requirements for cavity field amplitude and phase regulation.