CLASSE, Ithaca, New York
The maximum possible CW accelerating gradient in a superconducting cavity is often limited by a quench caused by a small defect on the RF surface. Sometimes the defect takes the form of a large (on the order of 100 microns) pit in the surface. In addition, the quench field for a pit is generally lower than for a normal-conducting defect with the same size. A brief survey of previous work and current theories on the nature and causes of quench is given, including recent theories on the quench mechanism of niobium pits.
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.
CLASSE, Ithaca, New York
The electric and magnetic field patterns of all modes in a cavity each form a complete set of eigenfunctions with the square of the mode angular frequency serving as the corresponding eigenvalue. Slater’s theorem provides a formula for predicting the first-order shift in the eigenvalue when the cavity surface is deformed slightly. A similar formula for predicting the shift in the eigenfunction (i.e. the field pattern) is derived from first principles. With this formula, it is possible to apply perturbation theory to find higher-order corrections to both the frequencies and the field patterns of a deformed cavity.