A high-voltage modulator for high-power RF source research

The design, construction, and operating results of a high-voltage modulator system capable of generating 700-kV, 2.5- mu s pulses at 5 p.p.s. into a load of 900 Omega are presented. The modular is used to energize a variety of high power microwave devices requiring voltage stability and reproducibility. Voltage ripple is less than 0.2% during the 1.0- mu s flat top, with a shot-to-shot voltage variation of less than 0.1%. The primary circuit consists of two seven-stage tunable Rayleigh-type pulse-forming networks (PFNs) connected in parallel with a total impedance of 2.25 Omega , a total capacitance of 0.56 mu F, and a total inductance of 2.8 mu H. The PFN is charged by a highly stable 80-kV capacitor charging power supply (0.1% RMS voltage ripple) at a rate of 10 KJ/s. The total energy stored (1.5 kJ) is released through an ITT F-187 thyratron into a 20:1 pulse transformer, which generates 700-kV, 2.5- mu s pulses. By changing the transformer, it was possible to obtain 250-kV, 1.70-kA pulses for driving low-impedance relativistic magnetron diodes. The flat-top voltage generated by the modulator is highly desirable for driving RF sources requiring high-quality electron beams, such as free-electron lasers (FELs) and cyclotron autoresonance masers (CARMs). The modulator performance in the relativistic magnetron and CARM experiments is described. >