Zur Mikrowellendiagnostik der Rauschtemperatur und der Trägerdichte eines Neonplasmas im Übergangsbereich zwischen der Freifall- und diffusionsbestimmten Säule

This paper deals with the experimental determination of the noise temperature and electron density. These plasma parameters were determined in the pressure region between diffusion and free-fall conditions with the aid of the microwave resonator method. In most cases the calculations of noise temperature and electron density were made using the energy distribution functions following from the electron Boltzmann equation. Great differences occur between calculated and measured values when the mean free path length of electrons becomes comparable with the dimensions of the discharge tube. These differences may be caused by a greater radial decrease of the noise temperature and/or by an increased interaction between boundary layer oscillations and plasma.     

Zur Mikrowellendiagnostik stromstarker Entladungen mit Skineffekt. Teil II: Bestimmung der Plasmaparameter eines angeströmten Stickstoffbogens bei Atmosphärendruck

Microwave diagnostics of an inhomogeneous, dense, cylindrical plasma column may be used to determine the complex impedance and a mean noise temperature in the range of strong skin effect (theory see part I). This case is realized if the specific d.c. impedance E/I falls below a critical value, e.g. 20 Ω/cm for ω = 10¹⁰. It is shown, that for any radial conductivity profile the complex impedance is a function of E/I only. A formula is derived for calculating the noise temperature of the column as a weighted mean value due to the local plasma temperature and conductivity. In the case of strong skin effect this mean value equals the electron temperature of plasma regions near the boundary of the conducting diameter. These results in connection with spectroscopical diagnostics are use to determine some plasma parameters of an arc discharge in a streaming nitrogen atmosphere at 760 Torr. The temperature profil was obtained from the intensity of the 3371 Å molecular band and then the conductivity profile was calculated using an energy balance equation. The results show that even in the 10 A-case the arc plasma is not in thermal equilibrium, the difference T_e—T_g being about 1,500 ºK. This large difference is due to the flow of neutral gas streaming downward the discharge chamber. The length of the discharge (1·3 cm) is not sufficient for the neutral atoms to reach their equilibrium temperature.     

Radiale Änderungen der Energieverteilungsfunktion der Elektronen im Plasma der positiven Säule elektrischer Entladungen

In the low-current positive column measurements of the electron energy distribution function show considerable changes in radial direction. At any point of the positive column of the Ne-discharge under investigation it is possible to approximate the energy distribution function by the Druyvesteyn-standard form. For the case of standard energy distribution functions a theory of positive column is developed which takes into account radial changes of electron temperature. Formulae for the calculation of radial behaviour of electron temperature, space potential, and radial electric field strength are given and compared with experimental results.     

Zur mikrophysikalischen Beschreibung des schwachionisierten Säulenplasmas von Glimmentladungen in Stickstoff-Neon-Gemischen. I. Vergleich zwischen gemessenen und berechneten Geschwindigkeitsverteilungsfunktionen der Elektronen

The isotropic part of the velocity distribution function of electrons is determined experimentally and theoretically for the plasma of the positive column of glow discharges in N₂-Ne mixtures. The distribution functions are measured with electrical probes using the Druyvesteyn method. The calculation of the isotropic part of the distribution functions for homogeneous and stationary conditions from the Boltzmann equation takes into consideration the essential elastical and unelastical collision processes. The character of the obtained distribution functions is fixed by the reduced field strength E/p₀ and the mixture ratio x = N₂/N₂ + Ne), which is varied in this paper in the range between pure nitrogen and pure neon. The distribution functions are found to be influenced by elastic and unelastic collisions of electrons with nitrogen molecules even at smal admixtures of N₂. Comparing the experimental results for the distribution functions with those received by the calculations a good agreement is observed.     

Örtliche Relaxation der Elektronen-Energieverteilung in hohen elektrischen Feldern

The motion of electrons in high electric fields is of particular interest due to its special experimental phenomena and its problems in theoretical treatment. We examine the spatial relaxation of electron energy distributions theoretically and experimentally. In the theory we assume a negligible elastic energy loss and a simple model for the inelastic collisions. The distribution function can be separated in two factors depending either on the kinetic energyε or on the total energyX=g3+Φ (Φ: potential energy). In application to the energy relaxation we calculate the relaxation of a humped initial energy distribution to a smoothed equilibrium distribution. The corresponding experiment was performed in the positive column of an argon plasma at a pressure of 3.6 · 10^?3 Torr. We measured the electron energy distribution as a function of distance from the cathode with a Langmuir probe using the second derivative method. Good agreement was found between the experimental and theoretical distributions.     

Investigation of the glow and contracted discharge plasmas in nitrogen by coherent anti-Stokes Raman spectroscopy,optical interferometry,and numerical simulation

The translational temperature in the plasma of glow and contracted discharges is measured using the methods of coherent anti-Stokes Raman spectroscopy and optical interferometry. The current density in the discharge is determined by measuring the electron concentration with optical interferometry and emission spectroscopy. The distribution of nitrogen molecules over vibrational and rotational levels in the ground state, the electron energy distribution, and the time dependence of the gas temperature are numerically found based on a model including the homogeneous Boltzmann equation and balance equations for the concentrations of charged and excited particles and for the gas temperature. The dynamics of transition to the quasi-steady-state distribution of nitrogen molecules over vibrational levels is studied.     

Studies of a light source based on the retardation of supersonic pulse discharge jets

The spectral distribution of the radiated energy of an imploded plasma formed through the collision of a super-sonic plasma jet of a pulse discharge against a stationary obstacle was studied. Its brightness temperature and absorption were measured. It is shown that the plasma can served as a source of a continuous spectrum with an energy distribution similar to that of an absolute blackbody. The brightness temperature of the source was variable over a broad range by appropriate adjustment of the discharge conditions.The authors are very grateful to M. A. El'yashevich for his interest in the present study and for his valuable comments on the results.     

Koinzidenzexperimente zum Elementarprozeß der Bremsstrahlungserzeugung

By using a coincidence method, the angular distribution of bremsstrahlung has been measured for definite energy loss and definite angle of the outgoing electron. The incident electron energy was 300 keV. With a magnetic spectrometer, outgoing electrons with an energy of 170 keV and scattering angles of 0°, 5° and 10° were selected. The electrons and photons were both detected in scintillation counters. A gold foil of 250 Å thickness served as the target. The experimental results are compared with theoretical calculations.     

Zur Mikrowellendiagnostik stromstarker Entladungen mit Skineffekt. Teil 1: Feldverteilung,Oberflächenimpedanz und Strahlungstransport

Using the methods of microwave diagnostics in the case of a dense, cylindrical plasma column, a complex surface impedance and a mean noise temperature, due to the real part of this impedance may be obtained instead of electron density, collision-frequency and noise (electron-) temperature in the usual low density case. In this paper these quantities including the scin-effect are calculated for the axial-symmetric plasma mode of an inhomogeneous plasma column. The mean noise temperature is obtained using a new method based on relations between the corresponding wave-equation and the four pole equations. The result is a differential equation similar to the equation of radiation transfer, but without the well known restrictions of this tool (approximation of ray optics, low damping of the wave).     

Interferometrische Bestimmung der Gastemperatur in der Stickstoffniederdruckentladung

A Michelson-interferometer in combination with a He-Ne-laser was used to determine the gas temperature in a nitrogen low pressure gas discharge. With this method the radial temperature profile could be measured to about 96% of the tube radius. Moreover rotational temperatures were measured with a 2 m-grating spectrograph from the spectrum of N₂- and N₂⁺-bands. In the range from 4 to 10 torr and 25 to 100 mA gas temperatures between 460 and 890 K were measured with the belonging rotational temperature from 620 to 1170 K. At pressures below 10 torr a difference of the rotational temperatures from the first negative and the second positive system was found. A qualitative consideration on the mechanism of the radial heat conductivity in the positive column was added.     

On the electron energy distribution in the gas discharge positive column: Langmuir paradox

The results of calculations of electron drift characteristics in a dc spatially inhomogeneous periodic electric field are presented. It is shown that the effect of field inhomogeneities on the drift velocity and the average electron energy is insignificant under typical conditions of experiments with gas-discharge plasma at low gas pressures. However, the intensity of the processes of excitation, ionization, and plasma spatial distribution are strongly affected by the inhomogeneity (variance) and field variation behavior. It is shown that the electric field inhomogeneity in the gas discharge positive column leads to maxwellization of the electron energy distribution function.     

Electron temperature measurement in a surface-wave-produced argon plasma at intermediate pressures

The main objective of this work is to obtain the electron temperature in an argon surface-wave-produced plasma column at intermediate gas pressures. After proving that argon upper excited states remain in Excitation Saturation Balance, the value of electron temperature along the plasma column has been obtained using a modified Saha equation and a corrected Boltzmann-plot. Moreover, the electron energy distribution function has been verified to be nearly Maxwellian in a 0.8-2.8 torr intermediate pressure range. Received 24 July 2000 and Received in final form 19 January 2001     

Die Energieaufnahme der Ionen in einem sehr schnellen Theta-Pinch

In a theta pinch with an extremely fast rising magnetic field (dB/dt 10¹¹ G/sec), a strong compression wave is produced in an initially fieldless low-density deuterium plasma. Assuming simple plasma models, a high-energy gain of the ions is expected already during the implosion of the plasma. In agreement with these calculations for a filling pressure of 20 μ D₂, a mean ion energy of 1–2 keV is determined from the first neutron emission at the end of the implosion, only 150 nsec after ignition. Decreasing the initial pressure to 10 μ D₂ does not cause any further increase of the achieved ion energy. This limitation of the ion heating is explained by a strong broadening of the current carrying layer at low densities which is observed by magnetic probe measurements. In the adiabatic compression, the mean ion energy attains values of several keV. During the first part of this phase, the energy distribution function of the ions is found to be essentially anisotropic, and monoenergetic rather than Maxwellian.     

狭缝微放电等离子体参数的光谱测量

利用平行管水电极介质阻挡放电装置,在氩气和空气混合气体中,得到了狭缝微放电等离子体。利用发射光谱法,研究了此放电中分子振动温度、分子转动温度和电子的平均能量随气体压强的变化。通过氮分子第二正带系(C3Πu→B3Πg)的发射谱线计算了氮分子的振动温度;利用氮分子离子(N2+)的第一负带系(B2Σu+→X2Σg+)的发射谱线计算了氮分子的转动温度;测量了氮分子离子391.4 nm和激发态的氮分子337.1 nm两条发射谱线的相对强度之比,研究了电子能量的变化。结果表明,当压强从60 kPa增大到100kPa,分子振动温度及分子转动温度均减小,氮分子离子谱线与激发态的氮分子谱线的强度之比亦减小。     

Geschwindigkeitsverteilung,Teilchendichte, transversale Driftgeschwindigkeit und Energiedichte des Neutralgases in der Freifallsäule unter Berücksichtigung der „Neutralgasaufzehrung”︁ durch die Ionisationsvorgänge

A neutral gas rarefaction caused by ionization processes occurs in the plasma of the low pressure gas discharges. The velocity distributions, the particle density, the transversal drift velocity and the energy density of the neutral gas are calculated both for the plane and for the cylindrical positive column under free fall conditions. The neutral gas rarefaction is taken into account. It is shown, that the velocity distributions is non-Maxwellian and anisotropic. The pressure tensor is anisotropic, too. Particle density and energy density of neutral gas decrease with increasing electron density and electron temperature relatively homogeneously over the cross section of the column. Only, if the degree of ionization is high, these densities are much smaller near the axis than at the wall. Decreasing neutral gas temperature causes a similar change in the particle density profile as increasing electron density and electron temperature do. The transverse neutral gas pressure decreases from the axis to the wall in all cases. In the steady-state column an upper limit exists for the transverse particle current density of the neutral gas and of the ion gas. This limit depends on the gas temperature, the filling pressure and the atomic mass of the filling gas. In the appendix the Boltzmann equation is given in a form, which is suitable to investigate cylindrical problems not only for simple examples.     

The influence of the state of a compressed thermonuclear substance on the combustion of inertial fusion targets under direct ignition by a short radiation pulse

One-dimensional numerical calculations were performed to study the dependence of conditions for initiating thermonuclear combustion and of the target gain of direct-ignition inertial fusion targets ignited by a short radiation pulse on the initial temperature of a preliminarily compressed fuel and the initial heat energy distribution between plasma electrons and ions in the ignition region (igniter). The igniter parameters at which an effective thermonuclear target explosion with a G ～ 10³ target gain occurred were shown to substantially depend on the initial temperature of the major fuel fraction and the initial heat energy distribution between igniter electrons and ions. The heat energy of the igniter passed a minimum as the size of the igniter decreased. The dependences of these minimum energies on the temperature of the major fuel fraction at various initial energy distributions between igniter electrons and ions were determined. An increase in the temperature of the major fuel fraction was shown to decrease the target gain.     

Measurement of Stark broadened profile of He(II) 4686A

Stark broadened profiles of the He(II) 4686A line were measured using a Z-pinch plasma as source. The electron density was determined from the halfwidth of the He(I) 3889 line and the temperature from the intensity ratio of the He(II) 4686 and the He(I) 3889 lines. The electron densities covered the range 0.5?2.3×10¹⁷ cm³ and the electron temperature was 4 eV. The plasma homogeneity was checked by varying the length of the column observed. The experimental profiles are in better agreement with the recent calculations of Greene than with the earlier calculations of Keeple.     

Energy losses and scattering of fast electrons in a dense plasma

This paper describes an algorithm for the calculation of specific energy losses and multiple scattering of fast electrons in a plasma, taking into account the interaction of the electrons of the beam with the bound and free plasma electrons and with the plasma. Results are presented of calculations for aluminum and lead plasmas with density 0.001-1 of normal and with temperature up to 1 keV for initial electron kinetic energy of 1 MeV. The energy-loss distribution in an aluminum plasma is calculated by the Monte-Carlo method.Tomsk Polytechnic University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 112–116, September, 1993.     

Study of uniformity of plasmas produced in a wall‐stabilized arc

In this contribution the plasma of an arc discharge in a mixture of helium and argon is studied. The gas mixture is introduced uniformly along the arc column between each of the stabilizing plates. From the measured lateral distribution of radiation (HeI, HI, ArI, ArII, NI, FI line intensity and width measurements), after Abel inversion, the radial temperature distributions were obtained at various positions of the arc column. Beside the expected radial temperature gradients, a distinct temperature gradient along the arc column was found.     

Das Abklingen des Plasmas der Impulslaser-Gasentladung in Stickstoff

For a typical laser gas discharge, the concentration and temperature of the most important plasma components at the end of the current pulse are calculated on the basis of given data for the tube radius, gas pressure, and energy input. Relating to a postdischarge time up to 1 s, the deionization, the association of the nitrogen atoms, the deexcitation of metastable molecules and the relaxation of the vibration temperature are investigated by means of simple balance equations. Finally the influence of plasma relicts on the following discharge pulse is discussed.