Theoretical models taking into account different feedback source terms (e.g., ion-impact electron emission, photo-electron emission, field emission, etc) have been proposed for the existence and explanation of the shape of negative corona current pulse, including the step on the leading edge. In the present work, a negative corona current pulse with the step on the leading edge is obtained in the presence of ion-impact electron emission feedback source only. The step on the leading edge is explained in terms of the plasma formation process and enhancement of the feedback source. Ionization wave-like movement toward the cathode is observed after the step. The conditions for the existence of current pulse, with and without the step on the leading edge, are also described. A qualitative comparison with earlier theoretical and experimental work is also included.
Toroidal electron clouds with a low aspect ratio (as small as 1.3) and lasting for thousands of poloidal rotation periods have been formed in the laboratory. Characteristic toroidal effects like a large inward shift of the minor axis of equipotential contours, elliptical and triangular deformations, etc., have been observed experimentally for the first time. The results of new analytic and numerical investigations of low-aspect-ratio electron cloud equilibria, which reproduce many of the observed features, are also presented.
An experiment simulating certain characteristics of the equatorial electrojet plasma (viz. Ve»re Vi ≳ ri) is described. High frequency (W ≳ Vi > ri) instabilities are observed when electrons stream in the E × B direction past ions with a velocity exceeding the ion acoustic speed. The observed phase velocities and frequencies agree with the results of the Farley‐Buneman instability theory, modified to take account of finite k∥. The measured instability spectrum for potential fluctuations goes as k−n⊥ with n = 2–3.5
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