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Electron properties in an atmospheric helium plasma jet determined by Thomson scattering

In this work we present Thomson scattering measurements on a nanosecond pulsed high voltage dielectric barrier discharge (DBD)-like helium plasma jet, operated in ambient air. With the low detection limit offered by a triple grating spectrograph equipped with a high quantum efficiency intensified charge-coupled device (ICCD) camera, temporally and spatially resolved electron densities and mean energies have been mapped. 7 kV peak with 250 ns width pulses at 20 kHz are applied to the inner cylindrical shaped electrode of a DBD. This results in a peculiar hollow electron density profile in the vicinity of the jet nozzle with maximum values of ne = 5 × 1018 m−3 and mean energies of up to 2.5 eV. Further downstream, the profile collapses radially and contracts. A much higher electron density is found (2 × 1019 m−3) while the mean energy is lower (0.5 eV).