Speaker
Description
A simulation code is under development for the solution of the time-dependent Boltzmann equation, self-consistently coupled with time-evolving nitrogen plasma chemistry of an electron beam driven discharge. The application is to a N2 filled chamber of pressure 0.1 to 10 Torr driven by the NRL 90 kV Febetron generator with a e-beam current pulse of 100 ns, peak current of 4 kA, and beam current density ranging from 25 to 300 A/cm$^2$. The code follows the time–dependent response of the electron energy distribution function (EEDF) to the changing electromagnetic field induced by the e-beam. During the e-beam pulse, the gas undergoes ionization and excitation due to collisions with the beam electrons with subsequent plasma chemistry. Processes included in the kinetics part of the model are electron-neutral and Coulomb collisions, vibrational excitation, electron collisional excitation, and ionization by plasma and beam electrons. The plasma chemistry module includes collisions with electrons, dissociation and dissociative ionization of N2 molecules. Conditions are such that the creation of secondary as well as later generations of plasma electrons by the e-beam are important. A circuit model of the 2D axisymmetric gas target solves for the electromagnetic fields and the return current density is computed from a generalized Ohm’s law. Plasma conductivity and the return current are studied in a wide range of gas pressure and e-beam current densities. The importance of individual plasma chemical processes and species production is evaluated.
*Work supported by NRL 6.1 Base Program.
