Design and Development of a Line-Type Pulsed Modulator Driver for S-Magnetron for Microwave–Plasma Interaction Experiments in SYMPLE

System for microwave–plasma experiments (SYMPLEs) is an experimental system setup in our laboratory for investigating the interaction of high-power microwave (HPM) with overdense plasma with plasma frequency $f_{\mathrm { pe}} \gt f_{\mu }$ , the wave frequency. The washer-gun plasma chosen for these experiments is pulsed ( $100~\mu $ s) and is operated in single-shot mode. The experimental campaign involves the excitation and launching of a pulsed ( $5~\mu $ s) microwave output from an S-Magnetron to the plasma at a predecided temporal regime where the plasma parameters satisfy the required critical requisites for the wave plasma interaction. Therefore it is necessary that the magnetron source is operated in single-shot mode, and the HPM output of all such shots is highly repetitive. The pulsed power driver for the magnetron should thus be capable of giving out highly reproducible (within ±5%) single-shot trapezoidal pulses of maximum 52 kV and 120 A current, with $5~\mu \text {s}$ flat top and about 5%–10% rise time, consistent with the requirement of the magnetron. As conventional solid-state modulators pose challenges in achieving shot-to-shot repeatability in single-shot operation, a pulse-forming network (PFN)-based modulator has been chosen despite the stringent pulse rise time requirements. A Guillemin Type-E line-type pulsed modulator has been designed, simulated, and developed indigenously in our laboratory. The design consideration includes the incorporation of a pulse transformer at the output of the pulsed modulator, with the magnetron load impedance of $433.33~\Omega $ constituting the secondary impedance. The primary impedance of $25~\Omega $ is treated as the load impedance for the pulsed modulator. The design approach has involved theoretical estimation of the per-section capacitance, inductance, and coupling coefficient values followed by simulation to determine the best suitable parameters for the 10-stage PFN. A setup consisting mainly of a high-voltage dc charging unit, the 10-stage PFN, a thyratron switch with an appropriate trigger module, and a pulse transformer withbifilar secondary windings has been developed and tested with dummy loads. Experimental results on dummy loads up to 35 kV output give highly reproducible (within ±5%) voltage and current pulses of $5~\mu \text {s}$ flat top and about 300–500 ns rise time. Details of the design, simulation, development, and test results of the line-type pulsed modulator are discussed in this article.