A HYBRID HYDRODYNAMIC-LIKE MODEL FOR PSEUDOSPARK DISCHARGE

A hybrid hydrodynamic-like formalism is presented for the study of the inception of breakdown and development of plasma bubble in the hollow cathode phase of a pseudospark switch discharge. It allows one to obt ain the spatio-temporal evolution of the electronic and ionic densitie s, velocities, and energies in fast transient situations in low pressu re discharges, This hybrid formalism allows the study of situations wh ere the mean free path is not low compared to the spatial variations o f the macroscopic parameters, and/or situations for which the transpor t energy (respectively, the transport velocity) is of the same order o f magnitude as the thermal energy (respectively, the thermal velocity) , as in the case of pseudospark discharge. The model is self-consisten t and its formalism stands on a particular representation of the aniso tropic nonlocal distribution function for electrons as baring a beam c omponent. The nonlocal electronic velocity is computed as a moment of the distribution function. The transport equations for mass and energy for electrons and ions are solved;by the Bur-corrected transport (FCT ) method where the source terms are calculated from the nonlocal distr ibution function, The electric field is calculated by the Poisson's eq uation. The discharge physics is modeled in both main gap and hollow c athode simultaneously to permit a correct coupling of the charged part icles, photons, and field between the two zones. Results show that the transport velocity and ionization growth for the case of highly aniso tropic nonlocal distribution function is largely higher than that base d on a pure hydrodynamic nearly Maxwellian distribution function, The energetic and high density positive ions impacting the inner walls and the back of the cathode hole participate in a composite effect yieldi ng a cathode surface phenomena of super dense secondary emission of el ectrons which enhances the plasma bubble inception inside the cathode hole, We propose a criterion for switch operation in the pseudospark m echanism based on the formation of the plasma bubble, inside the catho de hole, known as the hollow cathode phase, as a transition phase betw een the breakdown phase and the conduction phase.