Rise time analysis of pulsed klystron-modulator for efficiency improvement of linear colliders

In linear accelerators, the periods during the rise and fall of a klystron-modulator pulse cannot be used to generate RF power. Thus, these periods need to be minimized to get high e$ciency, especially in large-scale machines. In this paper, we present a simpli"ed and generalized voltage rise time function of a pulsed modulator with a high-power klystron load using the equivalent circuit analysis method. The optimum pulse waveform is generated when this pulsed power system is tuned with a damping factor of &0.85. The normalized rise time chart presented in this paper allows one to predict the rise time and pulse shape of the pulsed power system in general. The results can be summarized as follows: The large distributed capacitance in the pulse tank and operating parameters, < 4 ]„ 1 , where < 4 is load voltage and „ 1 is the pulse width, are the main factors determining the pulse rise time in the high-power RF system. With an RF pulse compression scheme, up to $3% ripple of the modulator voltage is allowed without serious loss of compressor e$ciency, which allows the modulator e$ciency to be improved as well. The wiring inductance should be minimized to get the fastest rise time. ( 2000 Elsevier Science B.V. All rights reserved.