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Experimental results obtained on the Tokamak de Varennes during a series of reproducible ohmic discharges are presented. Profiles of basic plasma parameters are constructed and compared with theoretical predictions. In particular, the measured plasma resistivity agrees with the neoclassical scaling rather than with Spitzer resistivity. The study of electron-density fluctuations indicates a linear dispersion relation with a propagation velocity of 3.0 × 104 cm s−1. Particle transport investigations are initiated, giving experimental diffusion and convection coefficients across the plasma radius for electrons and impurity ions.

If radiation of constant intensity W ionizes a gas of density ρ1 behind a window, a steady radiation front may be established and the gas will be heated, accelerated, and compressed. The properties of such radiation-induced waves are discussed as a function of the external parameters W and ρ1. With high absorber density ρ1 the radiation front acts like a "leaky piston" accelerating and compressing the neutral gas ahead, and leaving plasma of reduced density behind. This leads to the formation of a precursing shock wave travelling at vshock α (W/ρ1)1/3. The shock develops as a sharp spike near the Jouguet point which requires a sonic speeds a4 α (W/ρ1)J1/3in the ionized gas. With lower absorber density, the radiation front propagates as vr α W/ρ1 and accelerates and compresses the ionized gas at its rear. This plasma is then brought to rest and expanded in a subsequent rarefaction wave.

The formation of pressure waves, induced by the absorption of radiation in the Schumann–Runge continuum of oxygen, was studied experimentally and theoretically. The 10-μs radiation pulse, produced by a capillary discharge at a color temperature of 6 × 104 °K, passed through an LiF window into a test chamber containing oxygen. Surprisingly, the propagation velocity of the pressure waves was found to be independent of the initial filling pressure p0 (v = 364 ± 8 m/s); however, as expected, their point of formation behind the LiF window varied inversely as p0. The evolution of the pressure waves was computed numerically on the basis of a simplified model and the method of characteristics modified to include the radiant-energy input. It appears that the wave is driven for some time after the decay of the radiation pulse by release of frozen dissociation energy.