The effect of shear on turbulent diffusion in a microwave discharge plasma in a toroidal stellarator

Abstract

A toroidal ℓ = 3 stellarator with large shear (θmax < 0.25) is used to study the oscillations of a steady-state microwave discharge plasma, and the values of the correlation coefficient between density and electric field fluctuations and turbulent plasma fluxes are measured by the correlation method. It is shown that the oscillations observed are due to the drift-dissipative instability. The influence of shear on the amplitude of drift oscillations, on the cross-correlation coefficient and on the turbulent fluxes due to drift instabilities is analysed. A threshold value of shear (θcr ≈ 0.05) is found above which a substantial reduction in the oscillation level (⟨δne2⟨1/2/ne ∼θ−1.5) and in the magnitude of turbulent plasma fluxes (Γ̄ ∼ θ−3) can be noted.

Theory of dissipative drift instabilities in sheared magnetic fields

“…Finally, we note that the relevance of the present theoretical results to the Kharkov stellarator experiments [24] has been discussed by us in a separate paper [25].…”

Azimuthal distribution of divertor plasma fluxes in an ℓ = 3 stellarator and torsatron

“…It should be noted that the asymmetry in the radial plasma flux across the magnetic field has been observed earlier [11,12] in studies of the turbulent diffusion associated with drift oscillations.…”

“…These measurements were made on the J2 = 3 toroidal machine Saturn, which can operate in stellarator and torsatron regimes. The main parameters of the last magnetic surfaces of this machine are [12]: major radius R o = 36.5 cm, (averaged) minor radius 4 cm < F <6.5 cm, angle of rotational transform 0.1 < t < 0 . 5 , shear value 6 <0.25, and magnetic field strength H o = 3.1 kOe.…”

Studies of drift waves in a toroidal heliac

“…The electron temperature and the floating potential profiles are relatively flat over the whole plasma region. Flat and even slightly hollow electron temperature profiles have also been observed in low temperature argon plasma discharges in other devices (VOJTSENYA et al, 1977 ;FREDRICKSON and BELLAN, 1985), where the radiation was the dominant energy loss process.…”