Measurement of phase and amplitude variations in RF pulses of a linac and its evaluation with the electron beam

The amplitude and the phase of the pulsed RF power for the L-band electron linac at the Institute of Scientific and Industrial Research, Osaka University are measured with a diode detector and a double-balanced mixer. They are expected to be constant in the RF pulse because undulation of the flat-top of the high voltage pulse for klystron is reduced within ±0.13%, but the measured values were much larger than expected. In order to solve the contradiction, we have conduct experiments to measure the energy gain of the linac as a function of time in the RF pulse, which has the 4μs flat-top, using an electron beam with the 5ns duration and have found that the energy gain varies appreciably in the RF pulse. In an offline calibration experiment of the devices after the RF measurement, it turns out that the RF phase varies monotonously by 5.5deg in 2.7μs, which agrees quite well with the measured RF phase meter in a successive experiment. The energy gain calculated with the measured RF amplitude and the phase is qualitatively in agreement with the measured one, reasons of which are still in question. (author)