Charge transfer by high-energy electrons onto the leeward surfaces of a solid in a supersonic rarefied plasma flow

Abstract

Numerical and experimental dependence of equilibrium potentials of the leeward surfaces on the ratio of concentrations of high-energy electrons and positive ions in a supersonic rarefied plasma flow around a solid are obtained.Introduction. Electrodynamic interaction of solids with the polar ionosphere in the Earth's shadow is a superposition of two effects: irradiation by high-energy electrons and the flow of a "cold" rarefied plasma. If the concentration of positive ions near the body surface is N iw 10 4 cm −3 , negative charges up to a voltage of 1 kV are collected on the dielectric [1]. The main role in charging the solid surfaces in the polar ionosphere in the Earth's shadow belongs to hot electrons with energy from 1 to 35 keV (captured in radiation belts and propagating along the lines of magnetic force toward the Earth surface) and positive ions of the "cold" ionospheric plasma. The effects and consequences of high-voltage differential charging are most hazardous for the leeward surfaces of extended and electrodynamically large solids (R/λ ds > 10) and also for small solids in the near wake behind them [R is the characteristic size of the solid; λ ds = kT es /(4πe 2 N es ) is the Debye screening length of the undisturbed plasma, k is the Boltzmann constant, e is the electron charge, T es 0.3 eV is the temperature, and N es is the concentration of electrons in the "cold" plasma].The numerical study of high-voltage charging of the leeward surfaces of a solid in a polar plasma involves the solution of nonlinear integrodifferential Vlasov-Poisson equations for a supersonic flow and current-balance equations on the irradiated surface. The values of the coefficients of interaction between the charged particles and the surface for a particular material are determined experimentally.In the experimental study of high-voltage charging, it is necessary to reproduce the current density distribution in the near wake behind the solid in a supersonic rarefied plasma flow and simultaneous irradiation of the leeward surfaces by high-energy electrons with energy from 1 to 35 keV [1]. The test set designed for such studies has to combine the characteristics of a plasma gas-dynamic tunnel and an electrodynamic facility. The conditions of charging of dielectric solids in a polar plasma can be modeled (simulated) in a closed volume of such a test set. The difficulties of such studies are caused by the necessity of simultaneous implementation of conditions of plasma-gas-dynamic and electrophysical interactions in the solid-plasma system. The accuracy and reliability of the predicted level of charging of the leeward surfaces are determined by the agreement between the calculated values of the solid potentials and the data of ionospheric and test-set measurements.In the near wake behind an electrodynamically large solid, the concentration of positive ions of the "cold" plasma N is is several orders lower than its value N i∞ in the undisturbed plasma with an almost unchanged concentration of high-energy electrons N eh . This fact...

Probe diagnostics of laboratory and ionospheric rarefied plasma flows

“…For a wide parameter range of the plasma-probe system, the electron current to the cylindrical probe can be determined from the ratio [10] as .…”