Spatially and temporally resolved electron density measurements in streamers in dielectric liquids

• Spatially and temporally resolved spectroscopic measurements of light emitted from positive streamers in transformer oil are presented. Analyses of the measurements performed with a DC needle-plane gap yield electron densities and indications of the atomic excitation temperatures in the streamers. The hydrogen emission reveals an electron density below 10(16) cm(-3) during the main part of the streamer propagation time (80-90%). Later the light is also characterized by emission from a high-density plasma with electron densities in the range 10(18)-10(19) cm(-3). The electron density during this time increases approximately linearly with distance from the initiation point and a density factor of four higher has been measured at the streamer tip than at the root. Measurements with high spectral resolution detect both high and low electron densities simultaneously. A tentative model of the interior of the streamer plasma, spatially resolved, is presented.

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NATURVETENSKAP  -- Fysik -- Atom- och molekylfysik och optik (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences -- Atom and Molecular Physics and Optics (hsv//eng)

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