On the Response of an OST to a Point-like Heat Source

TL;DR

This paper investigates the response of Oscillating Superleak Transducers (OST) to a point-like heat source in superfluid helium, providing detailed experimental data and analysis of signal characteristics relevant for superconducting cavity diagnostics.

Contribution

It introduces a detailed experimental setup and analysis of OST responses to a controlled heat source, enhancing understanding of OST signal patterns and reflection effects.

Findings

OST signals start with a detectable negative pulse for real quench-like energy releases.

Reflection coefficient of the glass wall is measured as R = 0.39 +- 0.05.

OST spectra reveal three main frequencies interpreted as membrane oscillation modes.

Abstract

A new technique of superconducting cavity diagnostics has been introduced by D. Hartrill at Cornell University, Ithaca, USA. Oscillating Superleak Transducers (OST) detect the heat transferred from a cavity's quench point via "Second Sound" through the superfluid He bath, needed to cool the superconducting cavity. The observed response of an OST is a complex, but reproducible pattern of oscillations. A small helium evaporation cryostat was built which allows the investigation of the response of an OST in greater detail. The distance between a point-like electrical heater and the OST can be varied. The OST can be mounted either parallel or perpendicular to the plate, housing the heat source. If the artificial quench-point releases an amount of energy compatible to a real quench spot on a cavity's surface, the OST signal starts with a negative pulse, which is usually strong enough to allow automatic detection. Furthermore, the reflection of the Second Sound on the wall is observed. A reflection coefficient R = 0.39 +- 0.05 of the glass wall is measured. This excludes a strong influence of multiple reflections in the complex OST response. Fourier analyses show three main frequencies, found in all OST spectra. They can be interpreted as modes of an oscillating circular membrane.