Cryomodule Test Stand Reduced-Magnetic Support Design At Fermilab

TL;DR

This paper discusses the design and testing of a cryomodule test stand at Fermilab, focusing on reducing magnetic interference using low permeability materials to meet stringent quality factor requirements.

Contribution

It introduces a reduced-magnetic support design for cryomodules, including material selection and magnetic mitigation strategies for high-performance accelerator components.

Findings

Low permeability materials effectively reduce magnetic pollution.

Welding and machining processes are compatible with magnetic performance.

Design improvements meet the magnetic field specifications for cryomodule operation.

Abstract

In a partnership with SLAC National Accelerator Laboratory (SLAC) and Jefferson Lab, Fermilab will assemble and test 17 of the 35 total 1.3 GHz cryomodules for the Linac Coherent Light Source II (LCLS-II) Project. These devices will be tested at Fermilab's Cryomodule Test Facility (CMTF) within the Cryomodule Test Stand (CMTS-1) cave. The problem of magnetic pollution became one of major issues during design stage of the LCLS-II cryomodule as the average quality factor of the accelerating cavities is specified to be $2.7 \times 10^{10}$. One of the possible ways to mitigate the effect of stray magnetic fields and to keep it below the goal of 5 mGauss involves the application of low permeable materials. Initial permeability and magnetic measurement studies regarding the use of 316L stainless steel material indicated that cold work (machining) and heat affected zones from welding would be acceptable.