The magnetic field configuration of the Uragan-3M l=3 torsatron, which has a p=4 multipole vertical magnetic field compensation system, was studied using two methods to map the contours of the magnetic flux surfaces. The first method, the so-called triode method with a constant voltage electron source, measures the current emitted by an open thermoelectron emitter and the portion drawn by a highly transparent grid located in a poloidal cross-section of the torus. The second method involves the use of a conducting luminescent rod which scans the torus cross-section and lights up when struck by electrons emitted by an electron gun. The information on the magnetic surface structure obtained by these two techniques is compared. The characteristics of the two methods are discussed, giving special attention to the triode method because it allows an objective criterion for the quality of the magnetic surface structure to be introduced. It is shown how advantageous both methods are for rapid adjustment and optimization of the magnetic configurations in a stellarator when perturbations are present and what improvements could be achieved on Uragan-3M. Also discussed are experiments on generating electron clouds in Uragan-3M during the ramp-up phase of the magnetic field pulse

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.

If the major axes of the helical and vertical field coils of a torsatron plasma confinement device are not aligned to within ∼1% of their major radii, the resulting error field can break up closed magnetic flux surfaces and reduce the effective plasma confinement volume. A novel technique for accurately locating the magnetic symmetry axes of torsatron helical and vertical coil sets to within ∼1 mm using magnetic field measurements near the device major axis (i.e., away from the confinement volume) is described and applied to the URAGAN-3 torsatron. The axis of the vertical field coil set was found to be shifted by ∼1 cm relative to the axis of the helical coil set; this shift could account for the reduced confinement volume observed in previous experiments. The magnetic measurements were repeated after coil repositioning to verify correct alignment.

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