Speaker
Description
Here, we present simulation of a low-pressure, high voltage switch triggered by a laser pulse. The switch is held at a nominally high voltage in an environment absent of sufficient gas particles such that breakdown does not occur. Application of a controlled laser pulse to the cathode surface initiates injection of neutral material and electrons into the low-pressure gap. The increase in pressure allows for more frequent electron-neutral collisions, specifically ionization such that the switch begins to close. Injection of cathode material (carbon) is modeled using a first-principles model of the laser-cathode interaction that tracks the dynamics of electron and hole populations in momentum-resolved conduction and valence band states including carrier-carrier and carrier-phonon scattering. This scattering results in electron and lattice heating and results in thermal-field emission and cathode ablation. This laser-surface model is used to generate time-dependent fluxes of neutral and charged material which is then coupled to a Particle-in-Cell (PIC), Direct Simulation Monte Carlo (DSMC) code that simulates the subsequent plasma formation. Using a 500 mW laser with a 1 microsecond pulsed duration, the laser-surface model predicts a carbon neutral injection flux of 1028 m-2s-1 and a space charge limited electron current density of 200 A/cm2. The low-pressure switch is assumed to be filled with nitrogen gas at 1 torr with an applied voltage of 10 kV. Simulating the plasma formation leading to switch closure shows the formation of a high carbon density behind a traveling shock resulting from the expanding sublimated carbon and its interaction with the background nitrogen. As time proceeds, the integrated density across the gap becomes is much higher than one torr. As a result, electron ionization increases significantly across the gap causing plasma formation and initiating gap closure.
Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.
