Toroidal stellarator diode: discharge features and electron transport

Abstract

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.

Confinement jumps in a non-neutral plasma

“…Jumps in the cathode characteristic have been observed in both neutral and non-neutral plasmas. [1][2][3][4][5][6][7][8][9][10][11] These jumps have been studied in a variety of contexts. Some have studied the phenomenon in quasineutral plasmas, generally explaining the jumps in terms of processes that enhance ionization.…”

“…6 In non-neutral plasmas, sudden jumps in the emission current were observed when studying a method for mapping the magnetic surfaces in a stellarator. 7,8 Those studies focused on describing the characteristic and determining whether it was a problem for the surface mapping method rather than studying the jumps themselves. Those investigations showed that the voltage at which the jump occurs depends on certain parameters and suggested that the jump is caused by the action of a virtual cathode.…”