Speaker
Description
Mid-T (ca. 220 to 350°C) heat treatment is known to improve the dissipation of superconducting Nb cavities by dissolving the surface oxide and diffusing oxygen into the near-surface bulk. HZB explores the use of RF power coupled into the cavity as a technique to perform the heat treatment directly in the cryostat, thereby also avoiding venting and re-oxidation following the treatment. Such an RF-driven heating may be an attractive option for in-situ processing of an operation-ready accelerator module. We have demonstrated effective RF heating both with a TESLA-9-cell and a 1.5 GHz single-cell cavity reaching temperatures of 207°C (TESLA cavity) and 260°C (VSR single cell). Whilst the TESLA-cavity was driven via the fundamental power coupler using various modes of the fundamental passband, the single cell was heated using a higher-order mode at 4.263 GHz. The later was selected because of both its strong coupling and acceptable homogeneity of RF power dissipation. Experiments took place in two cryostats, HZB’s HoBiCaT and the Large Vertical Test Stand (LVTS), operated under elevated temperatures. In this paper, details of the experimental setup and process, heating performance and, in case of the single cell, a subsequent cold test are reported.
Funding Agency
Work supported by the Helmholtz association
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