One-dimensional semiempirical model of plasma in an accelerator with closed electron drifts
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ICLE ACCELERATION IN PLASMA
One-Dimensional Semiempirical Model of Plasma in an Accelerator with Closed Electron Drifts O. A. Gorshkov and A. A. Shagayda Keldysh Research Center, Onezhskaya ul. 8/10, Moscow, 125438 Russia Received May 21, 2007; in final form, October 23, 2007
Abstract—The plasma structure in an accelerator with closed electron drifts is investigated experimentally and numerically based on the measured data on the angular and energy ion distribution in a plasma jet. The mathematical model is constructed in a one-dimensional steady-state approximation and is aimed at calculating spatial distributions of the electric potential and plasma density in the region of the most intense ionization of neutral atoms. A comparison of the numerically calculated model potential distributions with the results from direct probe measurements shows that the proposed approach provides an online analysis of the plasma structure in the ionization–acceleration zone. PACS numbers: 52.59.Dk, 52.65.-y, 52.70.-m DOI: 10.1134/S1063780X08070076
1. INTRODUCTION The dependences of the local and global parameters of plasma accelerators with closed electron drifts (in particular, stationary plasma thrusters (SPTs)) on the power and discharge voltage were thoroughly investigated both theoretically and numerically (see, e.g., [1]), but the theory of gas discharges in such systems is still far from being complete. The main obstacle to constructing a complete theory and developing fast reliable numerical algorithms is the very complicated dynamics of the electron plasma component. Experimental and theoretical investigations show that the electron velocity distribution in the SPT plasma is highly nonequilibrium. This circumstance substantially lowers the reliability of the hydrodynamic description of the electron dynamics. The main difficulties in using the kinetic description and kinetic numerical methods (such as the particle-in-cell method) are associated with an enormous difference in the spatiotemporal scales characterizing the dynamics of electrons and heavy particles. For instance, the characteristic time for a neutral atom to cross the discharge region is approximately five orders of magnitude longer than the plasma period. A reliable simulation of the plasma in an SPT also requires accounting for complicated and insufficiently studied processes of the interaction of electrons with the discharge chamber walls. This is why existing numerical models cannot serve as a reliable tool for predicting the parameters of an accelerator at the design stage. In experimental studies of how the global parameters of the thruster depend on the geometry of the discharge chamber, the material of the chamber wall, the magnetic field topology, and other factors, the reasons
for the revealed characteristic features may remain unclear, as well as the applicability ranges of the formulas describing them. In such a case, it might be more efficient to develop a semiempirical approach in which an analytical or a numerical plasma model is constructed wi
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