Field profiling of resonant structure by an active circuit loop method

In conventional field probing of resonant accelerating structures that are high power RF devices for particle acceleration, the resonator under perturbation is being measured as a passive component by a network analyzer, with the procedure often being referred to as a bead-pull experiment. In this investigation, an alternative approach to measure the perturbed resonator by incorporating it within an oscillator loop is described. It has the advantages of simplicity in design and offering direct readout of the oscillator output frequency, which enables the electric field at the location of the dielectric bead to be readily determined. The theoretical basis and the experimental arrangement are described in detail. Measurement data obtained by this method for the axial field distribution of a resonant cell taken from an L-band coupled-cavity accelerating structure are presented.