The neutralization of space charge in the planar diode: II. By the injection of neutral particles

Abstract

The electrons produced by cathode emission in a plane diode generate positive ions by collisions in their passage through a thin sheet of neutral particles situated between and parallel to the electrodes. A nonrelativistic treatment of the charged particle motion enables the electron current to be calculated as a function of the electrode separation, the electrode potential difference, the density of the neutral sheet, the position of the sheet, and the cathode electric field. The maximum possible electron current is 459 times the electron Child-Langmuir limit and occurs for unique values of the position and density of the neutral sheet and also for zero cathode field. Cathode fields equal to several multiples of the average interelectrode field accompanied by currents equal to several multiples of the Child-Langmuir limit can be obtained by suitable choice of the neutral sheet parameters. Finally, it is shown that a neutral sheet of the required specifications can be formed by the effusion of mercury vapour through a suitably positioned slit.