Gepulste UV-Strahlungsquelle zur Erzeugung eines hoch ionisierten Ausgangsplasmas niedriger Dichte

A 100 kV Z-pinch, pulse-filled with high-density xenon gas, is used as radiation source for photoionizing hydrogen or rare gases at filling pressures of 1–10 mtorr. This produces a homogeneous, magnetic field free, highly ionized (degree of ionization ≈10% in H₂ and ≈ 20% in Ar) plasma suitable for example, for collisionless shock wave experiments. Experimental and theoretical investigations have yielded information on the conversion of the stored electrical energy into radiation energy. As a result of fast magnetic compression and ohmic heating (the relatively low temperature of max. 6 eV due to multiple ionization of the xenon atoms being favourable) the xenon pinch absorbs 30% of the stored electrical energy. Investigation of the matching of the external circuit to theZ-pinch by means of the snowplow model shows that the energy transmission efficiency could be increased about 50% if the current half-cycle is made equal to the compression time. The suitability of the xenon pinch as a radiation source is due on the one hand, to the almost complete conversion of the absorbed energy into radiation and, in particular, to the spectral distribution of the radiation, which is favourable for the ionization of hydrogen. It is found that the radiation is mainly emitted in lines with maximum intensity at the same wavelength λ ≈ 700 Å as the maximum of the photoionization cross section owing to the low temperature of the xenon plasma.     

Quantenstatistische Behandlung der Relaxation von Systemen mit mehreren Temperaturen

Equations for time dependent temperatures describing relaxation phenomena are deduced from quantum statistics. The basic concept is the selfconsistency of an observation level formed by partial energies of a system which means that the values of energies at a given timet determine the values at a later timet′ within macroscopic accuracy. The relaxation coefficients are expressed in terms of microscopic quantities.     

Diffusion eines stark ionisierten thermischen Plasmas im Magnetfeld. 2. Teil: Meßergebnisse

A thermal Cs-Plasma was produced by contact ionization at the surface of a hot tungsten helix spanned in the axis of a cylindrical glass vessel. The plasma density profile n (r, z) as a function of a magnetic field in z-direction was measured with a movable Langmuir-probe. In the present 2nd part the measured profiles are compared to the calculated ones, which are given in the 1st part. From this comparison the cross-section for collisions with the neutrals are calculated. Furthermore, the measurements show that diffusion perpendicular to the magnetic field takes place “classically”.     

Diffusion eines stark ionisierten thermischen Plasmas im Magnetfeld. 1. Teil: Berechnung des Dichteprofils

A thermal Cs-plasma was produced by contact ionization at the surface of a hot tungsten helix spanned in the axis of a cylindrical glass vessel. The plasma density profile n (r, z) as function of a magnetic field in z-direction was measured with a movable Langmuir-probe and compared to the calculated profiles. In the present 1st part n (r, z) is calculated from the diffusion equation. In the calculations collisions of the carriers with the neutrals as well as Coulomb collisions are taken into account. This leads to a nonlinear partial boundary value problem. Methods for numerical solution and numerical solutions are given.     

Bestimmung von Temperatur und Dichte eines Gleitfunkens aus der Bremsstrahlung im Infrarot

The absolute intensity of a vacuum sliding spark (length 2–10 cm, half cycle 0,8 μsec) has been measured in the spectral region between 0,4 and 3μ. From the long wavelength radiation emitted from an optically thick layer, one gets the temperature, from the short wavelength radiation emitted from an optically thin layer, one obtains the density. Using polyethylene as an insulator we reached a temperature of 4·10⁵ °K at electron densities of 8·10¹⁸ cm^?3 and current densities of 1.2·10⁶ A/cm². The temporal development of temperature and density has been determined. The maximum intensity at λ=0.43 μ was found to be 5·10⁴ (7·10¹⁰ W/cm³ ster) as large as that of the positive crater of a properly driven carbon arc. At λ=3 μ this same parameter turned out to be 300 times as large (5·10⁷ W/cm³ ster).     

Zum Einfluß von Kernladungszahl und Dichte bei der Stoffuntersuchung mittels Rückstreuung von Quantenstrahlung

Auf der Basis eines Einzelstreumodells wird die Intensität der rückgestreuten γ-Strahlung in Abhängigkeit von der Dichte und der Kernladungszahl des Streumaterials berechnet     

Allgemeine Berechnung der Elektronenverteilungsfunktion von schwach ionisierten Plasmen in beliebig zeitabhängigen elektromagnetischen Feldern

The behaviour of a weakly ionized plasma in external, arbitrarily time-dependent, electromagnetic fields is treated within the framework of kinetic theory. The Boltzmann kinetic equation is solved using the Lorentz ansatz, taking into account elastic collisions between electrons and neutral particles and assuming that the collision frequency is independent of the electron velocity. The drift velocity of electrons enters into the isotropic part f₀ and into the direction-dependent part f₁ of the electron distribution function. A method is given for the calculation of the drift velocity, which is calculated explicitly for the important but difficult case of a sinusoidal electric field in the presence of a magnetic switching field. f₀ and f₁ are calculated; f₀ is investigated generally. f₀ consists of an expansion in generalized Laguerre polynomials. The influence of the electromagnetic fields on the distribution function and its time variation is discussed and the relaxation behaviour is shown. The following two special cases are calculated explicitly: a linear rising electric field and a sinusoidal electric field, both in the presence of a constant magnetic field.     

Riesenmomente in stark verdünnten Legierungen von Fe in Ni3Ga

Mössbauer effect measurements were employed in order to study the magnetic behavior of very dilute alloys of Fe in Ni₃Ga. Extending the results of previous susceptibility measurements to the extremely low iron-concentration region a Brillouin fit yielded a giant moment of μ_eff=60 μ _b in Ni₃Ga(20 ppm Fe) the largest measured to date. The logarithmic concentration dependence of μ_eff revealed the limit of the molecular field model. Summarizing a comparison of Ni₃Ga(Fe) with Pd(Fe) is presented.     

Zur Ausbreitung von Ionenschall-Instabilitäten in schwach ionisierten Plasmen unter Berücksichtigung eines Potentialgradienten

A dispersion relation for the ion-acoustic instability in a dc-discharge is derived. The dc electric field term in the linearized Vlasov-equation is not neglected, and the ion drift velocity is taken into account. Collisions of the electrons and ions with the neutrals are considered on the basis of a Davy-dov-collision term. The influence of the dc field and the ion drift leads to higher values of the spatial growth rates in the low frequency range and a shift of the maximum of the growth rates and the high frequency boundary of the unstable waves toward lower frequencies. The phase velocity diminishes, what is, above all, a result of the consideration of the ion drift velocity.     

Zur allgemeinen kinetischen Theorie von partiell ionisierten Plasmen in zeitabhängigen Magnetfeldern und elektromagnetischen Zusatzfeldern

A general method is given for the calculation of the electron distribution function of a weakly ionized plasma in external time-dependent magnetic fields and additional electromagnetic fields. The Boltzmann equation of kinetic theory is solved taking into account elastic collisions between electrons and neutrals. The isotropic part f⁰ of the distribution function follows from a general linear integro-differential equation and contains all known standard distributions (Druyvesteyn, Davydov, Margenau and others) as special cases. The direction-dependent part f¹ gives the transport tensors.