A 100 kV, 20 A, 1 ms long pulse solid-state Marx modulator for klystron

Due to difficulties associated with the conventional gas tube based modulators, solid-state switch based klystron modulators are gaining popularity in the scientific community. Research, design, and development of high voltage solid-state modulators for electron and proton accelerators are in progress at Raja Ramanna Centre for Advanced Technology (RRCAT), Indore. A prototype of 100 kV, 20 A, 1 ms pulse duration Marx modulator has been designed and developed. The modulator has been constructed using 34 numbers of Insulated Gate Bipolar Transistors (IGBT), based 3 kV main modules for generation of a 100 kV base pulse. A droop correction scheme, consisting of 24 numbers of 1 kV corrector modules, has been adopted to compensate the droop in the output pulse. Before incorporating the droop compensation technique, the modulator had droop of 16% in the output voltage pulse. A microcontroller based control unit is used for the programmed staggered triggering of all the main modules and corrector modules. Fiber optic based control signal transmission was done to realize electrical isolation between high voltage circuits and control circuits. The modulator has been tested for 100 kV, 20 A, 1 ms pulse duration at 1 Hz, initially without droop compensation and later with the activation of the correction scheme for droop compensation. With the droop compensation scheme, less than 1% droop could be achieved in the output voltage pulse. Output voltage pulses of 1 ms pulse width, 1.4 μs rise time and 9.7 μs fall time at 100 kV have been achieved successfully. The present effort forms a strong basis for further development of this technology for higher average power as well as for replacing the earlier thyratron based modulators.