Prediction of electromagnetic pulse generation by picosecond avalanches in high-pressure air

摘要

The gas avalanche switch is a laser-activated, high-voltage switch, consisting of a set of pulse charged electrodes in a high-pressure gas. Induced electrons from a picosecond-scale laser pulse initiate an avalanche discharge between high-voltage and grounded electrodes. If the voltage, pressure, and dimensions are correct, the rapid avalanche, fueled by the immense number of electrons available in the gas, collapses the applied voltage in picoseconds and generates electromagnetic pulses with widths as short as 1--10 ps and 3 dB bandwidths of 20--120 GHz. With proper voltage or pressure detuning, wider pulses and lower bandwidths occur. A number of versions of the switch are possible. The simplest is a parallel plate capacitor, consisting of a gas between two parallel plate conductors. High voltage is applied across the two plates. A parallel plate, Blumlein geometry features a center electrode between two grounded parallel plates. This geometry emits a single pulse in each direction along the parallel plates. A frozen wave geometry with multiple, oppositely charged center electrodes will emit AC pulses. Series switches consisting of gas gaps between two electrodes are also possible. A recent investigation with 6 an overvolted series gap reported voltage switching times as short as 50 ps. For investigation of these switches, we have developed a two-dimensional, electromagnetic, finite difference, electron fluid computer code for ionization in high-pressure gases. This code simultaneously, self-consistently, and implicitly solves Maxwell's curl equations for transverse magnetic modes between perfectly conducting parallel plates. It solves electron fluid conservation equations for density, momentum, and energy. The coordinates are presently rectangular. Multiple charged, rectangular, perfect conductors may be situated between the plates.