Effect of alternating electric field on diffusion of weakly collisional plasma in ℓ = 1 Vint-20 torsatron

Experimental results are presented illustrating how a broad-spectrum alternating electric field affects superbanana plasma diffusion in the Vint-20 l = 1 torsatron with a large helical inhomogeneity of the magnetic field. The alternating electric field is excited in the frequency range of 2-30 MHz in a microwave discharge plasma with a density which is approximately greater than 10 to the 9th/cu cm, an electron temperature of approximately 5 eV, and cold ions. A description of the experimental procedure is presented. The parameters of the helical windings and the outermost magnetic surfaces are given, and a comparison of the experimental plasma containment times and the neoclassical theory predictions is made. It is shown that superbanana diffusion is reduced, which is manifested in a three-to-five-fold increase of the plasma density. Greatest effective influence of the electric field noise on plasma confinement is observed in an oscillation frequency range 3-4 times greater than has been estimated by averaging the magnetic field helical inhomogeneity values over the minor cross-section.