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Particle and energy fluxes in the scrape-off layer produced by poloidal limiters are studied in the JFT-2 tokamak with mean electron densities of 1.3 × 1013 and 2.8 × 1013 cm−3. The measurements were made by a combined Langmuir/thermoprobe and an infrared camera. The electron density in the scrape-off layer decays exponentially with increasing minor radius, implying that the cross-field diffusion is of the order of the Bohm diffusion. It is shown that heat transmission to the limiter more than 1 cm behind the edge radius is determined by a sheath of Maxwellian particles. Near the edge radius, accelerated electrons play a major role, which is indicated by toroidal anisotropy of the heat flux in the lower-density case.

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The dispersion relation for current-driven electromagnetic instabilities in an inhomogeneous slab geometry is derived and analyzed. We show that current in the direction of the equiii'onun magnetic field, as well as transverse w e n t gradients can strongly modify the drift-Alfven dispersion relation as given by ? LADOMTSEV (1965). If the perpendicular wavelength is much larger than the ion gyro-radius there can be fluid-like instabilities resulting from the interaction of the density gradient and current gradient with the parallel current. It is shown that weak parallel electron currents can produce instabilities which are stronger than the finite gyro-radius, density gradient and parallel flow shear instabilities previously derived by DOBROWOIS~Y (1972). Applications to G t e beta plasmas are discussed.