• Y. Xie, J.H. Hinnefeld, M. Liepe
  CLASSE, Ithaca, New York

To further the understanding of the r.f. performance of niobium and alternative superconducting materials such as MgB2, high field tests of material samples inserted into host microwave cavities are potentially highly beneficial. In this paper we present results from a detailed design study of such superconducting sample host cavities. The focus of the design work has been on maximizing the ratio of sample surface magnetic field to host cavity maximum surface field, on multiple mode operation to study frequency dependent effects, on mechanical stability of the host cavity under atmospheric pressure, and on choke joints between the sample plates and the host cavity.

• Y. Xie, M. Liepe, D. Meidlinger, H. Padamsee
  CLASSE, Ithaca, New York

A ring-type defect could be a better model for quench caused by the sharp boundary segment of a pure niobium pit. The relationship between quench field and inner radius of a ring-type defect is presented based on calculations of an improved ring-type defect model. Comparison between ring-type defects and disk-type defects model is also presented.

• Y. Xie, H. Padamsee, A. Romanenko
  CLASSE, Ithaca, New York

Pit-like structures are defect candidates that cause cavity quenches. Thermometry and SEM examination results of two such pit candidates are presented. The observed and simulated correlations between defects size and pre-heating temperature near the defect region at helium side can provide useful information about the effective defect size and resistance. Calculations based on a disk-type defect model suggest that the observed pit is much larger than the actual normal conducting region responsible for initiating the quench. This finding is consistent with the sharp edge segments of the pit as the possible regions responsible.