A simple model to describe the precursor generated in plasma focus discharges

The authors present a five fluid MHD stationary onedimensional model apt to describe the dissociation, ionization and heating of the molecular Deuterium located in front of the Plasma Focus Current Sheath (CS). The ultraviolet radiation emerging from the CS furnishes the energy to generate the precursor, through photoionization of molecules (D/sub 2/+h upsilon→D/sub 2//sup +/+e/sup -/; h upsilon≥15.4 eV) and atoms (D+h upsilon→D/sup +/+e/sup -/; h upsilon ≥13.6 eV), whereas the exothermic dissociative recombination (D/sup +/+e/sup -/→D+D) raises the temperature of the gas. Molecular dissociation by electronic impact (D/sub 2/+e/sup -/→D+D+e/sup -/; threshold = 4.4 eV) has been also included. All species are assumed to have the same temperature; the radiation from the CS is averaged over frequencies and direction of propagation; electronic thermal conduction and the emission of the radiation within the precursor are neglected; the relaxation times for rotational and vibrational molecular levels are assumed to be short enough so that the level populations follow Maxwell-Boltzmann statistics