A Monte-Carlo Code for Computing Transport Coefficients in Weakly Ionized Gas

Summary form only given. A Monte-Carlo code (MCSwarm) has been developed to provide transport coefficients in weakly ionized gases. The code can generate transport coefficients in crossed electric and magnetic fields for a wide varietv of gases including N₂, O₂, SF₆ , H₂, H₂O, Ar, Ne, CO₂, and He. The code follows many different interactions including rotational and vibrational modes, electronic excitation, ionization, and momentum transfer. The MC Swarm code provides an accurate method for computing electron mobility, ionization, and attachment rates suitable for particle-in-cell modeling of electron-beam-induced conductivity. The transport coefficients generated by MCSwarm are suitable at pressures above 1 torr. These coefficients have been incorporated into the fully electro-magnetic 3D PIC code Quicksilver (QS). To benchmark the QS model, we have modified an existing Febetron electron-beam pulser to produce an 100 ns electron beam pulses with a peak energy of 80 keV and a current density ranging from 1 A/cm² to 1 kA/cm². The net transported current 10 cm from the beam injection location agrees well with the QS simulations. The line-integrated electron density is measured by laser interferometry and also agrees well with the code calculations. The simulations show that emission boundary conditions are very important in determining where currents flow and that the effects of beam scattering in air are negligible for pressures below 20 torr. The code calculations further show that, for the parameters considered here, the electric field at high pressure is too small to cause avalanche and plasma production is dominated by beam-impact ionization.