The behaviour of an electron swarm in mixed oscillatory and unidirectional electric fields

Abstract

Measurements have been made in hydrogen, nitrogen, helium and neon on amolification of a stream of electrons crossing a parallel plate spark gap under the influence of combined ultra-high-frequency (40mc/sec) and unidirectional electric fields. Electrons generated thermionically inside one of the electrodes are injected into the gap through cylindrical holes in the flat face of the electrode, and cross the gap with a motion which is a fixture of drift and diffusion. At high enough values of the effective field in the gap, the electrons ray gain sufficient energy to produce ionization by collision. A theory is presented to explain the shape of the curves relating the amplification of the stream to the value of the applied uhf field for a given value of the do field (AMPLIFICATION CURVES). The predictions make use of values of the ionization coefficient obtained for the gases studied from breakdown measurements made in the same apparatus. The agreement between the calculated and experimental amplification curves is very encouraging in all the gases tested, being slightly better in hydrogen and nitrogen than in helium and neon. Qualitative explanations for this are put forward. Experiments have also been performed to investigate the effects of the raise of the emitting hole on the flow of electrons in the gap, mid it is shown that the hole dimensions are not important in determining the shape of the amplification curves. Long time constraints associated with the electron flow in the gap have been observed and studied in detail leading to the conclusion that when a current is passed in the gap, charging occurs at the electrode surfaces, assisted by the presence of insulating layers there. A method is suggested for the measurements of residual voltages thus generated.