Stoßbestimmte Relaxation des Elektronenensembles im Plasma bei zusätzlicher Aufheizung durch ein elektrisches Feld. III. Das periodische Verhalten der Elektronenkomponente im elektrischen Feld großen Modulationsgrades

Collision Dominated Relaxation of the Electron Ensemble in a Plasma with Additional Heating by an Electric Field. III. The Periodic Behaviour of the Electron Component in an Electric Field with a Large Modulation Amplitude With the aid of the non-stationary Boltzmann-equation the periodic behaviour of the isotropic part of the velocity distribution of electrons and thereby determined macroscopic quantities is calculated for periodic electric fields with large modulation amplitude. The investigations concern a weakly ionized column plasma in neon under typical low and medium pressure conditions. Based on the numerical results for typical ranges of field strength and cycle times of the electric field a qualitative physical interpretation for the periodic behaviour of the electron component is obtained. The introduction of special field-dependent adjustment times allows the formalution of conditions which characterize the case of quasi-stationary behaviour and also the case of small amplitudes of modulation in the macroscopic quantities determined by the isotropic distribution function. The periodic states between these two limiting cases can be interpreted as due to two competing processes. The first one is the energy input controlled by the electric field and the second one is the energy loss in binary collisions of the electrons with the atoms.     

Doppelresonanzuntersuchung des Einflusses eines elektrischen Feldes auf die Zeeman-Aufspaltung des 5s 5p 3P1-Terms im SrI-Spektrum

Under the simultaneous action of external electric and magnetic fields the 5s 5p ³ P ₁-level of the even Sr-isotopes splits into three non-equidistant Zeeman-sublevels. In an atomic beam experiment the spacings between the sublevels were investigated by the double resonance method at a magnetic field strength of ca. 22 Oe and at electric field strengths up to ca. 17 kV/cm. From the r.f.-resonance signals the tensor polarizability of the 5s 5p ³ P ₁-level was deduced to be α_ten(³ P ₁)=6.1(8) kHz/(kV/cm)². This value may be used to get an estimate of the oscillator strength of the infrared transitions between the multiplets 5s 5p ³P and 5s 4d ³ D. Taking into account oscillator strengths of electric dipole transitions to other low lying levels one obtainsf(³ P→³ D)≈0.09.     

Der Einfluß eines elektrischen Feldes auf Level-Crossings des 6d 2 D 3/2-Zustands im TlI-Spektrum

The influence of an electric field on the energy levels of the 6d²D_3/2-state in the Tl I-spectrum was studied by measuring the shifts of level crossing signals relative to their magnetic field positions. The following values of the magnetic hyperfine constantA and the Stark parameterβ were deduced: ¦A¦=42(2) Mc/sec · g_J/0.8, ¦β¦=0.12(1) Mc/sec/(kV/cm)² · g_J/0.8 and A/β>0. Assuming that the main part of the energy shifts are caused by admixtures of the 7p²P-states the sign of the Stark parameterβ and —from the measured ratio A/β>0 —the sign of theA-factor should be negative. For electric field strength E?30 kV/cm the energy shifts of the 6d²D_3/2state are considerably greater than the hyperfine structure splitting. Therefore the case of decoupled hyperfine structure is considered.     

Level-crossing-Experiment zur Untersuchung des Einflusses eines elektrischen Feldes auf die Hyperfeinstruktur des 4p 2 P 3/2-Terms im Cu I-Spektrum

Level-crossing technique applying parallel electric and magnetic fields has been used to investigate the influence of an electric fieldE _z on the hyperfine structure of the 4p ² P _3/2-state. The Stark shift of the level-crossing nearH _z =155 Oe and the modification of the magnetic zero-field level-crossing signal due to the electric fieldE _z was observed. Both experimental results can be explained with a Stark-constantβ=7.2(1.1)kc(kV/cm)^?2.     

Lichtelektrische Messung des inneren elektrischen Feldes in inhomogenen ...

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Lichtelektrische Messung des inneren elektrischen Feldes in inhomogenen ...

     

Die Verteilungen des elektrischen und magnetischen Mikrofeldes im relativistischen Plasma

The probability distributions of the electric and magnetic microfield at a fixed space point in a relativistic, non-degenerate, homogeneous, and isotropic plasma in thermodynamic equilibrium are determined using the Markov-method and neglecting the particle interaction. They are found to be Holtsmarkians like the electricnon-relativistic microfield distribution, but the characteristic field strengths are increasing functions of temperature which are calculated.     

Einfluß des elektrischen Feldes auf die fundamentale Absorptionskante von Bariumtitanat

The shift of the absorption edge of BaTiO₃ caused by an electric field has been measured in function of temperature and field strength. It shows a sharp maximum at the Curie pointT _C near 120°C, a linear field dependence belowT _C, and a quadratic field dependence aboveT _C. Furthermore this shift has the opposite sign to the Franz-Keldysh effect and is one or two orders of magnitude larger. This new effect is correlated with the electric polarization and is not induced by electromechanical lattice deformations. It is shown in a simple band model, that the relative displacement between the titanium and the oxygen sublattices induces an increase of the band gap, which agrees qualitatively with the experimental results.     

Die Elektronenbewegung im Neutralgas bei hohen elektrischen Feldern

In strong electric fields the acceleration of the electrons by the field exceeds the deceleration by collisions with neutral molecules. Thus run-away or beam electrons are produced. This paper investigates the motion of the beam electrons in a neutral gas considering ionization processes by electron-molecule-impacts. We start with a time independent current of primary electrons (case a) and a space independant density of primary electrons (case b). The further development of the velocity distribution is calculated. For a molecular hydrogen gas the amplification of the initial electrons, the average ionization, and the velocity distribution of the electrons as a function of space or time respectively is given. The average ionization has an asymptotic solution, which becomes valid, when one primary electron has produced by ionization an avalanche of approximately 100 electrons. The Townsend coefficient α for high values of the field strength is independant of space only in the region of this asymptotic solution.     

Das Verhalten des Koppelmann-Bogens im Unterschallbereich

A system of nonlinear partial integral-differential equations will be given which satisfies the single fluid model and describes the behaviour of electric arcs. A method to solve these equations simultaneously is outlined. The method is applied to an arc with Koppelmann geometry (radial gas injection into a wall stabilized arc). The behaviour of this arc is discussed on the basis of the numerical results obtained.     

Die Berücksichtigung der Ionisation durch Elektronenstoß in der Elektronenkinetik des schwachionisierten anisothermen Plasmas III. Das instationäre Verhalten bei großer impulsförmiger Feldstörung

The Influence of Ionization by Electron Collisions on the Electron Kinetics of the Low Ionized Anisothermal Plasmas The time behaviour of the electron component was calculated during the additional application of a single pulse to the electric field in the plasma. The investigations were performed for the weakly ionized Ne-plasma as a typical example taking into account supplementarily the direct ionization due to electron collisions and an electron loss term with a constant life time besides elastic and exciting collisions. Using the instationary Boltzmann equation we determined the time behaviour of the essential macroscopic quantities. Besides the caluclation of the marked temporal development of such quantities as the electron concentration, the electron collision frequencies for excitation and ionization and the different energy transfer rates especially the relaxation of the electron component was analysed after switch on and switch off the additional rectangular pulse.     

Die Relaxation der Geschwindigkeitsverteilungsfunktion der Elektronen im homogenen elektrischen Feld mit elastischen und anregenden Stößen. II. Das Verhalten des Elektronenensembles bei aperiodischer Feldänderung zwischen zwei stationären Zuständen

Recently the relaxation of the electron component was investigated under field-free conditions after sudden switch-off the electric field and otherwise after sudden changing the electric field to a new value of field strength. To continue these papers we consider now the relaxation process of the electron ensemble in the presence of a monotonous time variable electric field. The investigations are based on a computation of time change in the isotropic part of the velocity distribution function of the electrons and of the macroscopic parameters determined by the distribution function. The start-ing-point is the non-stationary Boltzmann equation with stationary initial states taking into consideration elastic and exciting collisions. Besides the representation of the received numerical results a physical interpretation is obtained for the duration of the whole relaxation process, for its initial stage as well as for the momentary stage of the relaxation by introduction of normalized characteristic time quantities. Further characterizing conditions are found related to the relaxation after quasi-jumplike change of the electric field and in the case of quasistationary field alteration respectively. With the introduced characteristic time quantities statements about the degree of realization of one of this limiting cases are possible for any given monotonous field. The investigations are per-formed in a low ionized non-thermal neon plasma.