10.6μm interferometry and Faraday rotation measurements on a θ-pinch plasma

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Abstract
The initial stages of a 40 kJ theta pinch in hydrogen at 13 mTorr have been investigated using a 10.6 mu m TEA CO2 laser. Electron density profiles measured across the tube using single-fringe interferometry show two imploding density fronts with a region of increased ionization at the tube axis when the first front approaches the axis. Electrons are swept up mainly by the outer front. 10.6 mu m Faraday rotation measurements of the magnetic field on the axis during the implosion stages are described. During the initial stages, the magnetic field is reversed with magnitude increasing to 0.4+or-0.01 Wb m-2 but changes direction at t=410 ns when the first density front approaches the axis.