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
The proposed Cornell Energy Recovery Linac (ERL) will be a 5 GeV, 100 mA cw electron accelerator using SRF Cavities. The cryomodule design will be an extension of TTF technology. The cryogenic plant will be a significant portion of the ERL cost and an accurate estimate of the heat load is crucial to facility planning. A prototype main linac cryomodule is in the process of being designed. The configuration of the major module components is sufficiently known to allow calculation of the cryogenic heat loads to the helium cooling circuits of 1.8K, 5K, and an intermediate temperature in the vicinity of 80K. The results of ANSYS thermal modeling with nonlinear material properties will be presented along with analytic calculations to provide an itemization of the cryomodule heat loads. The optimal intermediate temperature will be shown to be just above 80K. The wall-plug power for the cryoplant will be estimated with COP’s provided by major helium-refrigeration vendors.
CLASSE, Ithaca, New York
Broadband RF absorbing materials are frequently utilized in particle accelerator environments. There are stringent requirements placed on some of these absorbers in regard to vacuum compatibility, radiation compatibility, and particulate generation, especially for absorbers in close proximity to the beamline such as in some higher order mode (HOM) load designs. For RF absorbers located directly on the beamline, their DC conductivity must also be large enough to drain away static charge that may be deposited onto them, since such static charge could deflect the particle beam. Ceramics and ferrite materials have often been used for such RF absorbers, and SRF applications tend to extended their use to cryogenic temperatures. Unfortunately, the DC conductivity of these materials often drops precipitously with temperature and they become excellent insulators at cryogenic temperatures. The results of recent DC conductivity tests of several of these RF absorbing materials will be presented.