Thermodynamic Analyses of the LCLS-II Cryogenic Distribution System

TL;DR

This paper presents a detailed thermodynamic analysis of the cryogenic distribution system for the LCLS-II upgrade, focusing on heat loads, pressure drops, and system design considerations.

Contribution

It introduces a comprehensive thermodynamic modeling approach for the LCLS-II cryogenic system, addressing complex layout and operational requirements.

Findings

Identified key heat loads and pressure drops in the system.

Optimized the cryogenic distribution layout for efficiency.

Provided guidelines for pressure relief and safety measures.

Abstract

The Linac Coherent Light Source (LCLS) at Stanford Linear Accelerator Center (SLAC) is in the process of being upgraded to a superconducting radio frequency (SRF) accelerator and renamed LCLS-II. This upgrade requires thirty five 1.3 GHz SRF cryomodules (CM) and two 3.9 GHz CM. A cryogenic distribution system (CDS) is in development by Fermi National Accelerator Laboratory to interconnect the CM Linac with the cryogenic plant (CP). The CDS design utilizes cryogenic helium to support the CM operations with a high temperature thermal shield around 55 K, a low temperature thermal intercepts around 5 K, and a SRF cavity liquid helium supply and subatmospheric vapor return both around 2 K. Additionally the design must accommodate a Linac consisting of two parallel cryogenic strings, supported by two independent CP utilizing CDS components such as distribution boxes, transfer lines, feed caps and endcaps. The paper describes the overall layout of the cryogenic distribution system and the major thermodynamic factors which influence the CDS design including heat loads, pressure drops, temperature profiles, and pressure relieving requirements. In addition the paper describes how the models are created to perform the analyses.