Droop Reduction Control for μs Pulsed Power

Abstract

Droop in a rectangular pulse is a problem in klystron power supplies for next-generation particle accelerators. This paper presents a feedback control for droop reduction in a μs pulsed power, based on a framework for the control of short repetitive pulses newly introduced by the authors. The pulse waveform is sampled by a fast A/D converter. The inclination in a straight line fitted to the measured pulse top is used as the feedback variable representing the droop. The calculated variable is applied to modify the next generated pulse. An integral controller is built on the basis of measured characteristic curves that represent pulse generator's transfer characteristics, which look instantaneous to the controller acting slowly at the repetition rate of the pulse. As the control may increase high-frequency noises and the estimate for droop may be susceptible to drift in pulse phase, a condition for noise-resistant droop detection and a two-variables control of droop and phase are presented. The design procedure is illustrated and the effectiveness of the control is demonstrated in an experimental study on a 4μs 10kV/8A pulse generator with a hard FET switch. Iwata's compensating power supply was used for manipulating the waveform. The controlled droop was centered at zero with rms deviation less than 0.1%.