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Characterization of plasma conductivity by laser Thomson scattering in a high-voltage laser-triggered switch


High-voltage laser-triggered switches (HV-LTSs) are used in pulsed-power applications where low jitter and high current are required. The switches allow operation in the mega-ampere, megavolt regime while maintaining low insertion losses. Low inductance HV-LTS designs have shown discrepancies between modeled and experimental behavior, reinvigorating interest in the physics of HV-LTS operation. Detailed spatially- and temporally- resolved measurements of plasma properties within the switches could contribute to validating and advancing numeric models of these systems by checking the assumptions used in their derivation. To date, there is minimal experimental data detailing the evolution of plasma properties during switch operation. This work investigates HV-LTS plasma channel conductivity (the assumption within current models drawing the most critique) during the rising edge of the current pulse through both derivative (V-Dot) electrical probes and electron temperature measurements via laser Thomson scattering. A HV-LTS testbed utilizing an aqueous (variable impedance) resistive load was designed to produce experimental conditions found in larger pulsed power applications. This work describes the design of the load and experimental results under a variety of load conditions and operating voltages of 5 - 6 kV. The results indicate the electron temperature increases during the rising edge of the current pulse, suggesting that the plasma conductivity is temporally evolving. Further, electrical measurements show an increase in plasma conductivity during the rising edge of the current pulse. Evidence from both optical and electrical measurements calls into question the assumption of a temporally constant plasma conductivity as both the optical and electrical diagnostics show a temporally increasing plasma conductivity during the rising edge of the current pulse.


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Thomson scattering
laser triggered switch


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