Abstract
Discussion of the relative merits of so-called standing wave vis-a-vis travelling wave operation of linear accelerator waveguide is complicated by various considerations. In the first instance, standing wave should be distinguished from resonant operation. Standing wave operation is exactly the same as travelling wave, excepting that the waveguide is terminated by a total reflection of power instead of a matched load. It is probable that more accelerators are operated standing wave than travelling wave; formerly, medical and industrial accelerators were built with detuned or short-circuited terminations since there is no net energy gain (or loss) from the reflected wave. The only serious drawback to the scheme was that with long pulses the output power of an RF source is often determined by the VSWR of its load and that an RF window is possibly subjected to increased field stress, depending on its relative location with respect to the standing wave pattern. In resonant operation a length of slow wave structure is terminated, theoretically at reflection planes of symmetry; the discrete modes of resonance consist of two oppositely directed travelling wave ensembles, one of which will provide a space harmonic of an intended phase velocity.
Published Version
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