Oscillating Superleak Transducers For Quench Detection In Superconducting

Oscillating Superleak Transducers For Quench Detection In Superconducting ILC Cavities Cooled With Superfluid Helium Matthias Liepe Zachary Conway CLASSE, Cornell University June 1, 2009

Superconducting Cavity Defects • Localized electromagnetic power losses in a defect cause surface heating of both the defect and the adjacent superconducting surface. • In a sufficiently high electromagnetic field, the superconducting surface adjacent to the defect is heated to the superconducting to normal conducting phase-transition temperature. • Then the superconducting cavity becomes thermally unstable and the normal conducting region grows rapidly until all of the stored electromagnetic energy in the cavity is converted to heat. • i. e. the instability is manifested at a well-defined critical field level by a sudden collapse of the electromagnetic field in the resonator. • The time required for the collapse is typically 10 ms to 1 ms and is referred to as a cavity quench. 6/11/2021 Zachary A. Conway 2

Defect Location • Simple defect localization schemes can be implemented by exploiting the properties of superfluid He, e. g. second sound waves. • When a cavity quenches, typically several joules of thermal energy are transferred to the helium bath in a few microseconds. • If the cavity is operated at T < 2. 17 K, the helium bath is a superfluid and a second sound wave propagates away from the heated region of the cavity. • By locating several transducers in the helium bath around the cavity, the second sound wave front can be observed. The time of arrival of the second sound wave at a given transducer is determined by the time of flight from the heated region, which is centered on the defect causing quench. • Measuring the time of flight to 3 or more uniquely located transducers, unambiguously determines the defect location. 6/11/2021 Zachary A. Conway 3

Superconducting Cavity Defect Example • Defects are anything which cause the cavity to quench below the maximum theoretical critical field. • Pits, bumps, inclusions, surface contamination, sharp-pronounced grain boundaries, etc. 4 mm HAZ 6/11/2021 Zachary A. Conway 4

The Project • You will participate in the development of our second sound quench location system. • The primary goal will be to modify existing software and hardware to handle multiple unique cavity geometries and use the system to help locate defects. • Secondary areas: – Verify the accuracy of the software – Work on the development of the data acquisition hardware – Integrate the data acquisition with the quench location software – Participate in acquiring the cavity quench data 6/11/2021 Zachary A. Conway 5