Electron density and electron temperature in a neon plasma generated by 20-MeV protons

Abstract

The electron density and the electron temperature in a plasma, produced by irradiation of a neon gas with a beam of 20-MeV protons, has been studied. Various neon densities in the range from 1.5×10 23m -3 to 6.3×10 24m -3 and proton beam currents from 3 nA to 6 μA have been taken. By repeatedly pulsing the proton beam, such conditions were set up that the electron density was determined from the time dependence of the intensity of recombination-induced line radiation during the afterglow. From the relevant measurements it followed that the total cross-section for primary and secondary ionization of neon by 20-MeV protons is (1.7±0.3)×10 -21m 2. By comparing the observed time dependence of recombination-induced line radiation with the results obtained from a numerical model it could be concluded that the electron temperature in a plasma produced by a continuous proton beam of 6 μA in neon of density 6.3×10 24m -3, be three times as high as the gas temperature (room temperature). This could be ascribed to the energy transfer of fast secondary electrons to the bulk electrons in the plasma. Finally, the relative production in the plasma of 1s states and the relative population of 2p states obtained by the dissociative recombination process is measured for neon of density 3.7×10 24m -3 at room temperature.