On the Pressure Balance and Plasma Transport in Cylindrical Magnetized Arcs

Abstract

Magnetized current-carrying plasmas exhibit usually significant Ex B rotation velocities which often approach the ion thermal velocity. It is shown both experimentally and theoretically that this rotation in combination with inertia, viscosity and friction leads to an important reduction of the radial transport. If the radial electric field component is directed inward an inwardly directed force on the ions is set up. On the other hand, turbulence leads to enhanced transport especially at higher values of the electron Hall parameter. Also this effect is observed in this experiment and is shown to be in accordance with measured turbulence levels.

Investigation of oscillations and anomalous transport in a hydrogen hollow cathode discharge by a spatially three-dimensional two-fluid model

“…Thus, the (E ×B) drift frequency at any radial position r = R depends on the axial variation of the arc current flowing through the cross section of radius R. Similar arguments were discussed before in [32,48,52,53]. The plasma potential will increase from the plasma centre towards the plasma edge (∂ /∂r > 0), if the current carrying regions broadens from the cathode towards the anode (∂I (R)/∂z > 0; note that for the case discussed here j z < 0 and therefore I < 0, see figure 1).…”

“…The characteristic momentum transfer collision time for collisions between electrons and neutral particles is of the order of τ en ≈ 0.1 µs [44][45][46], so that the frictional forces acting on the electrons are mainly determined by electron-ion collisions, while the electron-neutral friction is negligible. Calculation of the collision times of the ions requires a knowledge of the ion temperature T i , which may be estimated from a simplified energy balance equation [32,33,40,47,48]. In this model one assumes that the ions are mainly heated by collisions with electrons, while they are cooled by collisions with neutral particles (momentum transfer and charge exchange) and by ion production from electron impact ionization of (cold) neutral particles.…”

“…For the plasma conditions investigated here it has been found convenient [32,41,48] to describe the plasma in terms of a two-fluid model. The basic transport equations will be formulated following the review paper by Braginskii [29], treating the plasma as a system of two fluids (electrons e and ions i), where each particle species s (s = e, i) will be described by a equation of continuity, a momentum balance and an energy balance equation.…”

“…The only remaining information for motivating the missing boundary condition at the cathode surface (Z k = 0) is the experimental value of the arc current I = −60 A. We, therefore, choose the axial electric field at the position Z k = 0, assuming a smooth (Gaussian) radial dependence with a radial 1/e length of 10 mm and adjusting the absolute value iteratively until the arc current calculated from equation (32) approaches the experimental values.…”

“…In this paper we present a summary and overview of the experimental results and the modelling of a magnetized hollow cathode arc discharge burning in hydrogen. The plasma of a similar discharge burning in argon has been investigated previously [10][11][12][32][33][34][35][36][37][38]. In these papers it was found, that the hollow cathode may be nearly described as a point source for the plasma, where the charge carriers are produced mainly in the cathode fall and then stream with high axial drift velocities along the magnetic field axis towards the anode.…”