CLASSE, Ithaca, New York
Superconducting RF cavity quench location is presently a cumbersome procedure requiring two or more expensive cold tests with large arrays of thermometers. One cold test identifies the cell-pair involved via quench field measurements. A second test follows with numerous fixed thermometers attached to the culprit cell-pair to identify the particular cell. A third measurement with many localized thermometers is necessary to zoom in on the quench spot. By operating superconducting RF cavities at temperatures below the λ point the second sound wave emanating from the location where quench occurred can be utilized to triangulate on the quench-spot. Here a method which utilizes a few (e.g. 8) oscillating superleak transducers (OST) to detect the He-II second sound wave driven by the defect induced quench is discussed. Results characterizing defect location with He-II second sound wave OST detection, corroborating measurements with carbon thermometers, and second sound aided cavity repairs will be presented.
CLASSE, Ithaca, New York
Cornell University’s superconducting cavity development program is one contributor to the global collaborative effort on critical SRF R&D for the ILC. We conduct R&D in support of the baseline cavity development as well as several alternate cavity development paths. For the baseline program we are preparing and testing ILC cavities. We have developed a new quench detection system and successfully applied it to ILC 9-cell and 1-cell cavities to find quench producing defects, which were characterized with subsequent optical examination. We have successfully repaired a 9-cell cavity using tumbling to raise the accelerating gradient from 15 to above 30 MV/m. We have identified quench producing defects in single-cell cavities using our large-scale thermometry system and subsequently extracted and inspected the defect region with an SEM. For the alternate R&D, we are developing reentrant cavity shapes with 70 mm and 60 mm apertures, and a simpler, potentially faster and less expensive electropolishing method called vertical electropolishing. We are also assisting in developing new cavity vendors by rapidly testing single-cell cavities they produced to qualify their fabrication methods.
CLASSE, Ithaca, New York
The RF superheating magnetic field of superconducting niobium was measured with a 1.3 GHz re-entrant cavity at several points in the temperature range from 1.9K to 4.2K. This experimental data is used to discriminate between two competing theories for the temperature dependent behavior of the RF superheating field. Measurements were made with <250 μs high power pulses (HPP, ∼1MW). Our test incorporated oscillating superleak transducers to determine the cavity quench locations and characterize changes and the migrations of the quench locations during processing. Using a vertically electropolished cavity, the temperature dependence of the superheating field was found to agree with Ginzburg-Landau predictions to within 10% down to a temperature of 4.2K; whereas prior to this experiment, theory and experiment only agreed at temperatures greater than 6.2K. We also used finite element methods to simulate the internal heating of the cavity, allowing for a more accurate measurement of superheating field as a function of temperature.
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
CLASSE, Ithaca, New York
FZD, Dresden
STFC/DL, Daresbury, Warrington, Cheshire
LBNL, Berkeley, California
Stanford University, Stanford, Califormia
TRIUMF, Vancouver
Cornell University, Ithaca, New York
DESY, Hamburg
The collaborative development of an optimised cavity/cryomodule solution for application on ERL facilities has now progressed to final assembly and testing of the cavity string components and their subsequent cryomodule integration. This paper outlines the testing and verification processes for the various cryomodule sub-components and details the methodology utilised for final cavity string integration. The paper also highlights the modifications required to integrate this new cryomodule into the existing ALICE cryo-plant facility at Daresbury Laboratory.