Thomson Scattering Measurements of Electron Density and Electron Temperature in a Nanosecond Pulse Surface Discharge

摘要

Time evolution of electron density and electron temperature in a near-surface discharge in helium has been studied using Thomson scattering. The nanosecond pulse, surface ionization wave discharge was produced using a custom-built, magnetic compression pulse generator (peak voltage up to ～12 kV, pulse duration 150 ns). The discharge was sustained between two copper electrodes separated by a 17 mm gap, at a pulse repetition rate of 120 Hz. A near-surface plasma layer approximately 1.3 mm thick was produced, at peak voltage of 6 kV and peak current of 80 A, coupling ～14 mJ/pulse to the plasma. Thomson spectra were collected for delay times ranging from 185 ns after the surface ionization wave was originated near the high voltage electrode, which is shortly after the wave reaches the grounded electrode, to ~1 us. Electron density and electron temperature in the near-surface plasma, ～1.1 mm from the dielectric surface, are inferred from the Thomson scattering spectra. Electron density values were found to be in the range of n_e ≈ 2·10~(13) to n_e ≈ 3·10~(14) cm~(-3) (peak value) while electron temperatures ranged from T_e ≈ 4.25 eV (peak value) to T_e ≈ 0.4 eV.