Experimental results on design aspects of a compact repetitive Marx generator

This paper presents the experimental results of a repetitive Marx generator being developed at BARC. Effect of lead inductance, sparkgaps´ alignment, charging inductor, ground inductor and shielding has been studied. Two types of configurations have been adopted in order to reduce the erected Marx inductance and results are compared. In this Marx generator plus-minus charging scheme was adopted for both test setups. Each setup comprised of 2-stage Marx with 4 series capacitors (each rated for 0.15 microfarad, 40nH, 50kV) while discharging giving 0.375 microfarads capacitance. In one of the scheme Type-I, all spark gaps were aligned in line of sight arrangements and successive discharge path were assembled in a zigzag manner so that the induced magnetic field gets cancelled out and effective inductance is reduced. This scheme was terminated to an aqueous load and critical matched condition was achieved at 12 ohm. This scheme had effective capacitance of 0.0375 microfarads, wave shape in lower voltage i.e. 10-15kV charging level. During experiments effect of load was also seen which gave half the open voltage to matched load [z=¿(L/C)] and in critical damping condition voltage was 0.7 times of open circuit voltage. These data will be used for developing a 6-stage 1.2 kJ Marx generator for 20 pps burst output. Presently testing is limited to 2pps due to charging power supply limitations. Thus the results can be summarized as follows: (i) line of sight and ultra violet triggering is not effective for a distance of 200mm, (ii) cancellation of induced magnetic field is not effective at 5kA current peak at 100mm distance, (iii) longer length leads in smaller diameter is preferable over larger diameter with smaller length assembly with zigzag leads for giving shorter pulse, higher current and faster rise time.