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P: Fachverband Plasmaphysik

P 18: Poster: Diagnostics

P 18.10: Poster

Donnerstag, 11. März 2010, 16:00–18:00, Lichthof

Electron density measurement in a pulsed-power plasma by laser interferometry — •Felix Mackel, Philipp Kempkes, Holger Stein, Jan Tenfelde, and Henning Soltwisch — Institut für Experimentalphysik V, Ruhr-Universität Bochum, 44780 Bochum

A pulsed-power experiment has been designed to produce arc-shaped magnetic flux tubes similar to ascending solar flares. The tubes are filled with hydrogen plasma (n_e≈ 10²¹ m⁻³) and expand with a velocity of 2.5 cm/µs, while keeping their minor radius of about 1.5 cm constant. In order to characterize the plasma regime and to investigate relevant MHD phenomena accurate data on parameters like electron density and mean energy are essential.

For measuring the line integrated electron density a laser interferometer is set up. A narrow cw CO₂ laser beam (λ = 9.3 µm, P ≈ 3 W, beam diameter typically 5 mm) traverses the vacuum vessel perpendicular to the plane of the plasma arc. It experiences a change in the optical path length when the flux tube passes by. The resulting phase shift is detected by measuring the light intensity after superposition with a reference beam. Time resolved measurements allow for the calculation of the radial electron density distribution in the flux tube if cylindrical symmetry is assumed and possible changes in the density profile during the passage are neglected.