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
The radial dependences of the emission current I em of a small thermionic emitter at different anode voltages, as well as the current-voltage characteristics (CVCs) and the dependence of I em on the magnetic field B were measured to investigate the relationship between the electron transport and the E × B electric and magnetic fields in the toroidal stellarator diode system in stellarator-type magnetic traps (Uragan-3M and Uragan-2M torsatrons). It is demonstrated that the electron transport in the discharge is controlled to a large measure by an applied radial electric field, while the current jump (nonlinear dynamic behaviour) in the discharge is due to the attainment of the critical value by the radial electric field and to the occurrence of the ionization process. A phenomenological description of the CVCs showing a hysteresis behaviour is presented. A large variety of electron transport scalings (I em -B dependences) were obtained in two different torsatrons.
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