Optical and Electrical Diagnostics of a High-Voltage Laser-Triggered Switch with Variable Impedance Load

Mega-Volt class High-Voltage Laser-Triggered Switches (HV-LTSs) are often simulated using the Martin/Braginskii model with sufficient accuracy to be largely predictive. However, recently developed switches operating with low inductance for nanosecond regime current pulses yield inconsistencies where the model both underpredicts rise times and overpredicts switch run time. The suspected reason for these inconsistencies lies in the model’s assumptions, specifically, that the plasma conductivity is both spatially and temporally uniform. This study investigates HV-LTS plasma channel conductivity 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 similar to those found in larger pulsed power applications. This paper describes the design of the load and experimental results under a variety of load conditions and operating voltages of order 5 - 6 kV. Our results indicate the electron temperature increases during the rising edge of the current pulse suggesting that the plasma conductivity is temporally dependent. 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 in our experimental setup. Finally, we show that Spitzer’s resistivity used by the Martin/Braginskii model does not accurately predict the measured plasma channel resistance.