H. Schlüter

High energy electron generation in surface-wave-produced plasmas

A theoretical model predicting production of hot electrons in the high-frequency field of surface-wave-produced plasmas is presented. The fast-particle generation is caused by the radial component of the surface-wave electric field near the boundary of the discharge by a mechanism so far not considered. As a result of acceleration, due to the interaction with the surface-wave field and due to energy loss by excitation and ionization of atoms in the main volume of the plasma, hot-electron tail of the energy distribution function is formed. The proposed mechanism of hot-electron generation is described for cases when the wave frequency is larger than the electron collision frequency.

Quasilinear theory of collisionless electron heating in radio frequency gas discharges

On the basis of quasilinear kinetic theory, the electron heating of rf discharges is treated for characteristic scale lengths of the heating field much shorter than the electron mean free path. The analysis considers plasmas bounded by walls providing specular reflection. The expressions for the coefficients of electron diffusion in energy space are obtained and analyzed for inductively and capacitively coupled plasmas. Accounting for the oscillatory spatial structure of the penetrating electric field in the regime of anomalous skin effect leads to a decrease of the diffusion coefficient for high, and an increase for low, energy electrons. It is shown that the presence of a second boundary in the case of collisionless plasma slabs results in a similar effect. The formation of energy distribution functions in various regimes of collisionless heating is discussed. The diffusion coefficients are presented taking into account ambipolar electric fields.

Determination of electron energy distribution functions in surface wave produced plasmas. I. Modelling

For surface wave produced argon plasmas in the 60-180 MHz range, electron energy distribution functions are calculated from the electron Boltzmann equation solved in the Lorentz approximation. Breakdown and maintenance field strengths are determined self-consistently by satisfying additional balance equations. The influence of space charge fields and the limits of the approximations used are discussed.

Nonlinearity: Basis for self‐consistent modeling of surface wave produced plasmas in diffusion controlled regimes

A fluid model of surface wave produced discharges is presented for diffusion controlled regimes taking into account simultaneously nonlinear contributions from stepwise ionization and volume recombination. The saturation of metastable densities with growing electron density reduces the effect of step ionization and allows recombination to become effective toward high electron densities. The charged particle continuity and energy balance equations linking electron density and electric field intensity yield the plasma permittivity under conditions of strong ionization nonlinearity. This permittivity is valid for high frequency discharges in general. In the second part of the modeling this nonlinear permittivity is introduced into the electrodynamical relations for discharges maintained by the field of traveling surface waves, and subsequently the self‐consistent behavior of plasma and wave characteristics along the discharge length is calculated. Both the main part of the discharge column produced by Joule ...

Pulsed discharges produced by high-power surface waves

The mechanisms of the ionization front advance in surface-wave-produced discharges are investigated using two experimental set-ups. The high-power surface waves are excited in a 3 cm wavelength band by a surfaguide and a novel type of launcher (an E-plane junction). The ionization front velocity of the surface wave is measured for a wide range of gas pressures, incident microwave power and initial pre-ionization. The experimental results are compared with theoretical ones based on three different models. The comparison between theory and experiment allows one to suggest a new interpretation of the ionization fronts advance. The ionization front velocity is determined by a breakdown wave or an ionization wave in the electric field of a high-power surface wave in the zone near the ionization front.

On the influence of Coulomb collisions on the electron energy distribution function of surface wave produced argon plasmas

The effect of Coulomb collisions on the electron energy distribution function (EEDF) in surface-wave produced argon plasmas in the RF and microwave regime is studied via solution of the Boltzmann equation, including a Fokker-Planck term, in the well known Lorentz approximation. The maintenance field strength is determined self-consistently by simultaneously solving a particle balance equation subjected to a boundary condition, which accounts for the sheath formation at the wall. The modifications to the EEDF and some derived parameters introduced by the Coulomb collisions will be discussed. The theoretical predictions are compared to experimental results, which have been obtained by a Langmuir probe technique on a surface-wave produced argon discharge at 60 MHz.

Determination of electron energy distribution functions in surface wave produced plasmas. II. Measurements

For pt.I see ibid., vol.24, p.1585-93 (1991). Electron energy distribution functions of surface wave produced argon plasmas are measured via second derivatives of Langmuir probe characteristics. An active compensation method for avoiding modifications by the RF electric field is employed. Good agreement with previous numerical solutions of the Boltzmann equation is observed.

The influence of the plasma resonance heating on the maintenance of surface wave produced discharges

On the basis of the equations of hydrodynamics the radial temperature distribution of charged particles in surface wave produced plasmas is investigated, taking into account the nonlocal heating effect caused by the enhanced radial component of the electric field in the presence of a plasma resonance region. It is shown that because of the latter effect the maintenance of the discharge may be mostly due to the enhanced radial component of the surface wave. The temperature of electrons and ions are shown to have maximum values near the wall of the discharge tube.

Wave-sustained discharges in helium–argon gas mixtures

A numerical fluid-plasma model of diffusion-controlled surface-wave-sustained discharges in helium–argon gas mixtures is presented. Owing to a detailed description of the ion dynamics, with effective ion-mobility and ion ambipolar-diffusion coefficients introduced, variation of the gas components from 100% argon up to 100% helium is permitted. After dealing with the radial structure of the discharge, the model finally provides results for the interrelated axial variations of the discharge characteristics: wave number and wave space damping rate, power absorbed on average by an electron, electron density and electron temperature, as well as ion densities, which are additional characteristics compared to discharges in pure gases. Because of both applications and spectroscopy diagnostics, a 2.45 GHz discharge at a total gas pressure p=1 Torr is chosen for discussions. The influence of the ratio of atom concentration of the gases in the mixture on the discharge structure is shown. Although only slightly modif...

Theory on electromagnetic surface wave propagation in inhomogeneous plasmas

Effects of plasma density nonuniformity on the surface wave propagation along plasma-plasma and plasma-dielectric interfaces are investigated. Plasma inhomogeneities in longitudinal and transverse directions with respect to the direction of wave propagation are considered. The influence of the inhomogeneity on the propagation properties (dispersion, absorption) of the surface waves and the space distribution of the wave fields is analyzed. The wave behavior in the region of the quasi-static surface wave resonance is also studied.