Investigation of local losses as a function of material removal in a large-grain superconducting niobium cavity
The performance of a superconducting radio-frequency (RF) cavity made of residual resistivity ratio (RRR) > 200 large-grain niobium has been investigated as a function of material removal, between 70 and 240 mu-m, by buffered chemical polishing (BCP). Temperature maps of the cavity surface at 1.7 and 2 K were taken for each step of chemical etching and revealed localized losses (hot-spots), which contribute to the degradation of the cavity quality factor as a function of the RF surface field. It was found that the number of hot-spots decreased for larger material removal. Interestingly, the losses at the hot-spots at different locations evolved differently for successive material removal. The cavity achieved peak surface magnetic fields of about of 130 mT and was limited mostly by thermal quench. By measuring the temperature dependence of the surface resistance (Rs) at low field between 4.2 K and 1.7 K, the variation of material parameters such as the energy gap at 0 K, the residual resistance and the mean free path as a function of material removal could also be investigated. This contribution shows the results of the RF tests along with the temperature maps and the analysis of the losses caused by the "hot-spots."
- Research Organization:
- Thomas Jefferson National Accelerator Facility, Newport News, VA
- Sponsoring Organization:
- USDOE - Office of Science (SC)
- DOE Contract Number:
- AC05-84ER40150
- OSTI ID:
- 921501
- Report Number(s):
- JLAB-ACC-06-519; DOE/ER/40150-3997
- Country of Publication:
- United States
- Language:
- English
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