The expansion phase of the high current vacuum arc: M R Barrault and R L Haywood, Proc of 11th Internat Conf on Phenom in Ioniz Gases, Prague 1973, 79

Abstract

Electrohydrodynamic sources have been proposed as thrusters in electric space propulsion. Compared with chemical propulsion, electric propulsion is characterized by a relatively low thrust and high exhaust velocity of the propellant. These inherent characteristics of electric propulsion offer direct applications in space missions. A study of a field emission electric propulsion system has centered around an emitter modular unit. This module has evolved from a simple single-pin or point source emitter, through linear arrays of stacked needles to the solid slit type emitter module used by Bartoli et al. [J. Phys. D: Appl. Phys. L7 (1984) 2473; J. IEEE Trans. Plasma Sci. P515 (1987) 593]. To model the device, Mitterauer assumed the liquid metal emitter to be an infinitely long cylinder. In order to preserve the symmetry and make the problem tractable, he assumed the accelerator electrode to be a concentric cylinder, which was then used to study the condition for the onset of instability within a surface capillary wave model. Although this model can be used to estimate the field, it does not exhibit the actual geometry associated with the finite size in the device. In this paper, we use a more accurate model to simulate the experimental configuration. The electric field distributions for a finite slit-type liquid metal charged particle source emitter with a parallel planar anode are calculated using an analytic truncated series solution of Laplace's equation. This approach obviates the difficulties of the finite element method which becomes computationally less efficient when there are large gradients in the electric field. The form of the charge density on the emitter is approximated by a truncated series whose coefficients are determined by the boundary conditions on the emitter and the anode. The electric potential and field distribution are determined in both the plane perpendicular to the slit and in the plane of the slit. The calculated field distribution, as a function of scale of the device, suggests the significance of geometry for controlling the spatial characteristics of the emitted current density.