Variation in the parameters of an electron cloud expanding in plasma and vacuum

Abstract

The dynamics of an electron cloud expanding under the action of an electric force from its uncompensated volume charge in vacuum and with allowance for the friction force in plasma is studied in the hydrodynamic approximation. The variations in the electric field strength, velocity, density, and electron current in the cloud with time and distance are determined. For the motion of an electron cloud in a plasma, the moment is found when the electron velocity on the edge of the cloud vanishes, which can lead to the rise of back currents and intersections of electron trajectories in the cloud. It is shown that, if an electron cloud moves in vacuum, this phenomenon is impossible and the parameters of the flow tend with time to their asymptotic values. The maximum cross section area of an electron cloud with a concentration exceeding a given one is found.