Analysis and design of parallel-coupled high-gradient structure for ultrashort input power pulses

Abstract

Shortening the pulse length of input power is a possible approach to raise the accelerating gradient limit of normal conducting structures. We present a novel design of a parallel-coupled structure that operates at ultrashort input power pulses. The principle of the design is to shorten the filling time of the whole structure by feeding the cells individually so that the duration of power transmission between cells can be saved. An X-band (11.994 GHz) parallel-coupled structure design with a 10 ns pulse length is presented in this work. Previous high-power tests of X-band structure prototypes show that a gradient of 120 MV/m could be achieved for a 200 ns pulse length. Based on the law requiring that E^{30}t^{5}=constant, this 10-ns-structure design should be able to reach a gradient of 200 MV/m. A detailed circuit model and real-time electromagnetic field simulation methods for designing the parallel-coupling structure are also presented and discussed in this paper.