Date Thesis Awarded

5-2020

Document Type

Honors Thesis

Degree Name

Bachelors of Science (BS)

Department

Physics

Advisor

George Vahala

Committee Members

Richard Marcus

Keith Griffioen

Abstract

Superconducting Radio Frequency (SRF) cavities play a fundamental role in particle accelerators. Efficient operation depends on expelling magnetic flux from the cavity, and any residual flux that remains trapped after cooling below the critical temperature can have a significant impact on performance. Experimental evidence suggests that material defects as well as cooling protocols can have a strong impact on subsequent performance. To better understand these phenomena, we use time-dependent Ginzburg-Landau theory implemented as finite-element simulations. We adapt the theory to allow spatial variation of material-specific parameters along with realistic temperature dependencies. We report on numerical experiments for different configurations of defects such as pinning sites and grain boundaries, finding that grain boundaries have a much larger effect than pinning sites on the ability of a superconductor to expel magnetic flux. We also report on numerical experiments where we investigated effects of cooling speeds on magnetic flux expulsion, observing qualitative changes which occur when we change a parameter which controls the time dynamics of our simulations. We discuss implications for SRF cavity design and operation as well as future research.

Creative Commons License

Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 License.

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