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P: Plasmaphysik
P 9: Dense Plasmas and Plasma Diagnostic (Poster Session)
P 9.16: Poster
Dienstag, 3. April 2001, 12:30–15:00, AT2
Measurement of the Electron Density in Laser Initiated Plasma Channels by Spectroscopy and Interferometry — •Christoph Niemann1, Dan Penache2, Frank B. Rosmej2, Andreas Tauschwitz2, Renate Knobloch1, Stefan Neff1, Radu Presura1, R.W. Lee3, and Dieter H.H. Hoffmann2 — 1Gesellschaft fuer Schwerionenforschung, Planckstr. 1, 64291 Darmstadt — 2TU-Darmstadt, Schlossgartenstr. 1, 64291 Darmstadt — 3Lawrence Livermore National Laboratory, USA
Laser initiated, free standing discharge channels offer many attractive advantages for the transport and focusing of intense ion beams. Discharge plasmas can neutralize both current and space charge of such beams, while the azimuthal magnetic field provides strong focusing all the way through the channel. Experiments at GSI have produced 50 cm long stable plasma channels with peak currents in excess of 40 kA in 2 to 20 mbar NH3 gas fill. Gas heating along the desired path of breakdown by a CO2 laser pulse tuned to a vibrational resonance line of the ammonia sets the proper initial conditions for the discharge. Spectral and temporal resolved measurements of the plasma self emission as well as interferometry have been performed at the GSI channel. Electron densities are derived from the Stark broadening of the hydrogen Balmer lines. Electron temperature determination based on the emission of nitrogen lines from several charge states will be discussed. An imaging Michelson interferometer at 1064 nm and 532 nm is used to measure the refractive index space resolved and to distinguish between effects of the electrons and the gas. Results of both methods are compared.