Date of Award

Spring 2026

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Mechanical & Aerospace Engineering

Committee Director

Tian-Bing Xu

Committee Member

Drew Landman

Committee Member

Gianluigi Ciovati

Abstract

The Thomas Jefferson National Accelerator Facility (Jefferson Lab) is currently developing a prototype conduction-cooled 915 MHz SRF cryomodule proposed for industrial use, capable of increasing the energy of an electron beam with 5 mA current by ~ 4 MeV. Two Nb3Sn resonant cavities are under development for this project, in which cryogenic cooling is provided by closed cycle refrigerators (cryocoolers). One cavity utilizes high-purity electroformed copper on the outer surface to provide heat extraction from the cavity, the other relies on high-purity aluminum thermal links. This thesis investigated the thermal conduction pathways between the cavities and cryocooler cold heads, with emphasis on minimizing thermal contact resistance in the thermal link assembly of the latter cavity, as well as the development of a dedicated shipping fixture to provide safe transport of both cavity assemblies for testing at an external facility. Experimental measurements and finite-element analyses (FEA) were conducted on joints composed of high residual resistivity ratio (RRR) niobium, oxygen-free high conductivity (OFHC) copper, and 99.999% (5N) purity aluminum bulk plate materials, as well as 99.99% purity indium foil and Apiezon N thermal grease interfacial materials, intended to provide the thermal pathway from cavity to the cryocoolers. The results indicated the use of Al–Nb joints with an indium foil interfacial, as well as Al–Cu joints with an Apiezon-N interfacial layer provided sufficient thermal performance to support continuous-wave (CW) operation at the target accelerating gradient. Furthermore, pressure distribution measurements validated analytical pressure distribution models and FEA as useful tools for asymmetric bolted joint assemblies. In addition, single-degree of freedom (SDOF) analytical models and FEA were used to design and evaluate a shipping fixture assembly employing wire rope isolators. The FEA results indicate good agreement with the SDOF model used to select the isolators, and show adequate attenuation of both the vibrational and shock environments to ensure safe transport of the hermetic cavity assemblies.

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DOI

https://doi.org/10.25777/k86k-j145

ISBN

9798197809346

ORCID

0009-0001-2358-5924

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