Theoretical model of suppression of electron instability in Hall thrusters by boundary feedback system

Summary form only given. Plasma instabilities in Hall thruster (HT) deteriorate the performance of the thruster and its compatibility with the electronic equipment of the spacecraft. Therefore, a development of effective methods of suppressing the instabilities is an actual problem. Among the plasma instabilities in HT, large scale electron instability holds one of the main positions. Its arising brings about redistribution of electrical field in the acceleration layer that can increase losses of ions on the walls of the thruster. In Ref (1, 2), the theoretical model of the electron instability, based on Rayleigh mechanism of its arising, was developed. The application of a feedback system is a versatile method of suppressing the large scale plasma instabilities. Two kinds of the feedback system are possible: volume and boundary (surface) ones. At conditions of the HT, the boundary feedback system (BFS) is more preferable. At an application of the BFS, sensors and controlling electrodes are placed on the plasma boundary, which is parallel to the magnetic field, that is, on an anode³. For the correct choice of the BFS parameters, a theoretical model of the electron instability suppression by the BFS was first developed. It is a subject of the presentation.The theoretical model is built in hydrodynamic approximation with cold magnetized electrons. The perturbations are assumed to be two-dimensional and potential. It is assumed that BFS creates an azimuthal distribution of the potential on the surface of the anode which is function of the electrical field perturbation near the anode. The boundary eigenvalue problem is solved. From the solution, the requirements to the transformation coefficient of the BFS are defined. It is shown that in the frame of made assumptions, the suppression of the electron instability is possible for all lengths of the wave. . For the suppression of the electron instability, the transformation coefficient should lie in the region,- limited as a lower value, so an upper value, which depend on the length of wave and the distance from the anode, where the unperturbed drift velocity sharply increases. The physical mechanism of the electron instability suppression is considered.