Momentengleichungen für Plasmen mit anisotropem Neutralgasdruck und anisotropem Ionendruck

Strongly non-Maxwellian and non-isotropic velocity distributions of the neutral atoms and of the ions occur in collisionless plasmas at high degrees of ionization, especially in gas discharges at low pressures and high current densities and in high temperature plasmas. The velocity distributions and the related velocity moments for the neutral gas and the ion gas are calculated. The influence of the magnetic fields on the ions is neglected. Especially, the pressure tensors and the heat flow tensors are investigated. The differential equations are given for the velocity moments of the velocity distribution. Additional terms occur in the equation of motion, if the pressure is non-isotropic and non-Cartesian coordinates are used. A heat flow tensor is evaluated that closes the system of differential equations for the neutral gas consistently and allows to rederive typical formulas of the molecular neutral gas flow. The heat flow tensor essentially determines the type of the differential equation system for the velocity moments. It is shown, that the neutral gas temperature is not constant across the plasma. Different statements deal with the heat flow tensor in the ion gas. In particular, non-vanishing ion temperature on the axis and a system of differential equations for the positive column under free-fall conditions are investigated. The inertia terms for the ion gas and the neutral gas must be taken into account in the pressure balance of the plasma.     

E-H-Zyklotronechos in Plasmen

A new echo type with free electrons in a slight inhomogeneous magnetic field excited by one electric and one magnetic pulse is calculated. Thus features of cyclotron echos and spin echoes are combined. The first electric pulse accelerates all (cold) particles to the same velocity as in the case of usual cyclotron echoes. The second magnetic pulse (at t = τ) rotates the plane of precession in phase space, quite in analogy to the motion of magnetic moments in the case of spin echoes. The echo arises at t = 2τ. The E-H echoes make relaxation and diffusion measurements in plasmas possible, using the methods proved useful in spin echo technique. There are no complications as in the case of E-E cyclotron echoes which are based on the fact that a velocity-dependent collision frequency is necessary for the nonlinearity of that echo mechanism.     

Über stationäre,rotierende, inkompressible Plasmen mit minimalen inneren Verlusten

The condition that the Ohmic and the friction losses are minimized leads to the assumption that both the magnetic field H and the velocity field v are Trkal-fields. . In the rotationally symmetric, stationary case the boundary conditions and the condition that the toroidal part of v and H should vanish on the boundary, lead to a linear eigenvalue problem for α, β which in case of a rectangular domain easily can be resolved. It follows: .     

Photoabsorption on nuclei

We calculate the total photoabsorption cross section on nuclei in the energy range from 300 MeV to 1 GeV within the framework of a semi-classical phase space model. Besides medium modifications like Fermi motion and Pauli blocking we focus on the collision broadening of the involved resonances. The resonance contributions to the elementary cross section are fixed by fits to partial wave amplitudes of pion photoproduction. The cross sections for NR → NN, needed for the calculation of collision broadening, are obtained by detailed balance from a fit to NN → NNπ cross sections. We show that a reasonable collision broadening is not able to explain the experimentally observed disappearance of the D₁₃(1520)-resonance in the photoabsorption cross section on nuclei.     

Die Bremsstrahlung von Plasmen bei geringer Ionisation

It is shown, that the continuous spectrum (free-free radiation) of a plasma in a thermal equilibrium — if the degree of ionization is slight — is produced not only by the electron-ion impacts, but also to a considerable extent by the impacts of electrons with the neutral atoms. Under this assumption the radiation of a mercury arc plasma in the infra-red is calculated. The results are in good agreement with absolute radiation measurements in a wide range of frequencies and pressures.     

Photoabsorption cross section of titanium to cobalt

Calculations of the photoabsorption cross section of the elements TiCo are compared with recent measurements. The structure seen near the 3p ionization threshold is explained by the large 3p–3d oscillator strength and the short lifetime of the 3p hole due to a super Coster-Kronig transition.     

Photoabsorption cross section of the Thomas-Fermi atom

The photoabsorption cross section σ(ω) and the distribution of oscillator strengths df/dω [these values are related as σ=(2π²e²/mc)(df/dω)] were determined for an atom with a large Z value using the semiclassical approach. These values were found for low frequencies with the use of the Vlasov kinetic equations, which were numerically solved by the method of particles. The asymptotic behavior of the distribution of oscillator strengths at high frequencies was determined by semiclassical equations for the photoabsorption cross section of electron shells in a Coulomb potential. The asymptotic equations were used to suggest an interpolation equation for the distribution of oscillator strengths over the whole Thomas-Fermi frequency range 27 eV ? ?ω ? 27Z² eV. This equation was used to calculate the logarithmic mean excitation energy, which appears in problems of ionization loss of charged particles. The distribution of oscillator strengths in a neutral atom allows the radiative properties of dense matter to be determined.     

High-Energy Two-Electron Photoabsorption as a Three-Body Problem

We study the high-energy behaviour of double photoionization and of the ionization accompanied by excitation of the states n¹S and n³S of the H^– ion, helium atom, and light helium-like ions. We show that the high-energy nonrelativistic limit of the ionization+excitation to the single-ionization cross section ratio is still valid for the photon energies, corresponding to the relativistic energies of the outgoing electron. The same applies to the double photoionization of the triplet states. The situation for the double photoionization of singlet states differs due to the quasifree mechanism. All these ionization ratios are calculated by using the high-precision locally correct wave functions for the bound electrons. The importance of using locally correct functions is emphasized.     

Bestimmung von Normtemperaturen für nichtthermische Plasmen

The normal temperatures are calculated for an optical thin plasma which is not in local thermodynamic equilibrium. The following cases are investigated:

1. 1.
   The normal temperatures for spectral lines of neutral atoms.     
   
   

Zur Theorie der Plasmen bei Anwesenheit magnetischer Felder

Based on the Boltzmann equation a complete theory of stationary cylindrical plasma is obtained considering the presence of the self-magnetic field as well as an additional longitudinal magnetic field. The effect of electron-electron interaction is thoroughly included by expansions in terms of Sonine polynomials. The formulae of the current density and heat flow components of n-th order approximation explicitely determined here are derived in terms of mean free paths which depend on the directions of transport as well as of the producing gradient. In the same manner the corresponding components for a Lorentz plasma are given.