Development of a high-resolution measurement technique of the interval between bunches in a linac with coherent transition radiation

A new technique of measurement of the inter-bunch distance has been developed. The interval between bunches in the L-band linear accelerator was measured with the cross-correlation interferogram of coherent transition radiation emitted from successive bunches in the millimeter wave region. The radiation was detected by a fast far-infrared bolometer and a fast-gated integrator after passing through an interferometer. The periodic fluctuation of the inter-bunch distance was observed in the time structure of a 4-μs macro-pulse. The maximum amplitude of the fluctuation was 60 fs and corresponds to the resolution of 0.01% compared to the interval between bunches of 769 ps which was calculated from the accelerating radio frequency of 1.3 GHz (L-band).