A New Method of Measuring Gap Voltages and Parallel Resistances of Cavities

A new method of measuring voltages across cavity gaps and deducing the cavity's parallel resistance is discussed. The method is based on velocity modulation of a beam of monoenergetic charged particles (electrons) from a radioactive source. The change in the line spectra of an energy-selective particle detector (a semiconductor detector), when the particles pass through the gap, is used for calculating the cavity gap voltage. Combination with a measurement of the power dissipated in the cavity gives the value of the parallel resistance. A description is given of a practical arrangement together with experimental results.