Quench-Spot Detection for Superconducting Accelerator Cavities Via Flow Visualization in Superfluid Helium-4

Shiran Bao and Wei Guo
Phys. Rev. Applied 11, 044003 – Published 1 April 2019

Abstract

Superconducting radio-frequency (SRF) cavities, cooled by superfluid helium-4 (He II), are key components in modern particle accelerators. Quenches in SRF cavities caused by Joule heating from local surface defects can severely limit the maximum achievable accelerating field. Existing methods for quench-spot detection include temperature mapping and second-sound triangulation. These methods are useful but also have known limitations. Here we describe an alternative method for surface quench-spot detection by visualizing the heat transfer in He II via tracking He2 molecular tracer lines. A proof-of-concept experiment is conducted, in which a miniature heater mounted on a plate is pulsed on to simulate a surface quench spot. A He2 tracer line created nearby the heater deforms due to the counterflow heat transfer in He II. By analyzing the tracer-line deformation, we well reproduce the heater location within a few hundred microns, which clearly demonstrates the feasibility of this alternative technology. Our analysis also reveals that the heat content transported in He II is only a small fraction of the total input heat energy. We show that the remaining energy is essentially consumed in the formation of a cavitation zone near the heater. By estimating the size of this cavitation zone, we discuss how the existence of the cavitation zone may explain a decades-long puzzle observed in many past second-sound triangulation experiments.

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  • Received 9 December 2018

DOI:https://doi.org/10.1103/PhysRevApplied.11.044003

© 2019 American Physical Society

Physics Subject Headings (PhySH)

Accelerators & BeamsCondensed Matter, Materials & Applied Physics

Authors & Affiliations

Shiran Bao1,2 and Wei Guo1,2,*

  • 1National High Magnetic Field Laboratory, 1800 East Paul Dirac Drive, Tallahassee, Florida 32310, USA
  • 2Mechanical Engineering Department, Florida State University, Tallahassee, Florida 32310, USA

  • *wguo@magnet.fsu.edu

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Vol. 11, Iss. 4 — April 2019

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