Change In Electron Temperature Research Articles

Nonlinear transmission characteristics of the plasma sheath

Abstract : A model is constructed of a nonlinear, one dimensional inhomogeneous multicomponent plasma slab which has the characteristics of the plasma sheath surrounding a typical hypersonic re-entry vehicle at 200,000 ft while traveling at about 18,000 ft/second. A plane wave incident upon the slab at arbitrary angle can induce changes in electron temperature without affecting the neutral gas temperature. The variations of electron temperature produce changes in collision frequency and the rate coefficients describing the various electron production and loss mechanisms. Such changes cause alterations in the effective dielectric constant of the medium. On the basis of a model of a plane-layered medium composed of a stack of linear homogeneous sheets, the reflection and transmission coefficients of the nonlinear slab may be computed by a step-by-step numerical integration of Maxwell's equations expressed in the form of difference equations.

An Experimental Study of the `Electron' and `Vibrational' Temperatures in Low Pressure Discharges Through Nitrogen

The dependence of the electron temperatures on tube diameter, discharge current and pressure in a low pressure discharge through N2 has been investigated, the electron temperatures being obtained by the Langmuir probe method. Under identical experimental conditions, `effective' vibrational temperatures have been determined from intensity measurements on the second positive band system of nitrogen. From these results an attempt has been made to correlate the changes in electron temperatures with those in vibrational temperatures. Paschen curves for tubes with three different diameters were also determined to assist in the interpretation of the data.

Flow of Low-Density High-Speed Plasma through a Magnetic Barrier

The barrier transmission ratio I/I0 of a stream of plasma can be evaluated from theory in terms of the temperatures and masses of the ions and electrons, the speed of the stream, and the ratio ΔB/B0 of the height ΔB of the barrier field above the guiding field B0. All of these parameters were measured for a hydrogen plasma except the ion temperature Ti. Johnson-Malter double-probe data yielded at the maximum density point of the stream a plasma speed of 1.3 × 107 cm sec−1, a number density of 5 × 1013 cm−3, and an electron temperature T̃e = 3.5 ± 0.2 ev for B0 = 780 gauss at the position of the barrier. I/I0 decreased to 0.5 for ΔB/B0 = 17.8 at which point a theoretical curve has been fitted with T̃i = 7.1 ev; this value for T̃i was confirmed by application of the equipartition theory of Spitzer to the observed change of electron temperature with time.

Thermal Conductivity of an Electron Gas in a Gaseous Plasma

The thermal conductivity of an electron gas in a gaseous plasma is determined by experimental techniques which have been improved over those reported in a previous article by Goldstein and Sekiguchi. A pulsed microwave is utilized to probe the plasma parameters as well as to selectively heat up the electron gas in a small volume of the elongated plasma. The photomultiplier tube detects the change in electron temperature by taking advantage of the phenomenon of afterglow quenching. The experimental values for the thermal conductivity, which are determined by two different methods, are in good agreement. In the plasmas investigated, neon and helium, the degree of ionization is very low (${10}^{\ensuremath{-}5}$-${10}^{\ensuremath{-}6}$). However, the measured values of the thermal conductivity are still consistent with those obtained from the theoretical expression given by Landshoff, or Spitzer and H\arm for a fully ionized gas.

The structure of a shock wave in a fully ionized gas

The structure of a plane shock wave moving through a completely ionized plasma of protons and electrons is calculated. It is assumed that the two species of particles behave as two gases, each separately in a quasi-equilibrium state corresponding generally to two different temperatures. Navier-Stokes type equations with coefficients of viscosity and thermal conductivity appropriate to the two species are solved by numerical iteration.For very strong shocks it is found that both the velocity of electrons and protons and the temperature of the protons change in a distance about twice the mean path for momentum transfer between protons in the hot (shocked) gas. The electron temperature changes in about eight of these mean free paths, causing a relatively wide zone of hot electrons at low density ahead of the usual velocity shock-front. The density and temperature gradients of protons and electrons create an electric field.

Change of Electron Temperature in an Electron Beam

The effect of electron encounters on the velocity distribution in an electron beam after passage through an accelerating grid is calculated by direct integration of the Boltzmann equation. It is found, with electron densities and velocities typical of traveling wave tubes and diodes, that the electron encounters have a negligible effect, that the formulas of the usual kinetic theory for heat conduction do not hold, and that the longitudinal component of the electron gas pressure is negligible.

Influence of a Longitudinal Magnetic Field on an Electrical Discharge in Mercury Vapor at Low Pressure

The effect of a uniform longitudinal magnetic field on a low pressure arc has been investigated in an arc tube with a Hull type cathode and movable and fixed probes. The magnetic field collimated the current flow from the cathode into a luminous beam which disappeared rather abruptly 30 cm from the cathode into a tube-filling glow. This glow was more intense at the axis than in the absence of field. By making the field more intense at the cathode the beam was made to fill the tube and the subsequent glow was indistinguishable from that observed in the absence of field. It thus appeared that a uniform field exercised no constrictive effect on the arc. Distortion of the probe characteristics by the field limited the range within which the probes could be used to low field values at which interesting magnetic effects were still weak. It was demonstrable that the field imparted a transverse stiffness to the arc which caused the transmission of a disturbed condition over large distances in the direction of electron flow. The measurements showed that there was no marked change in electron temperature, gradient, or electron concentration in the presence of a field, and indicated that the limiting cross-sectional distribution of charge as transmitted disturbances die out is the same as in the absence of field. The change of transverse potential distribution with field was found to be roughly in accordance with the modified Boltzmann distribution for the electrons which was previously derived theoretically.

The Rate of Change of Electron Temperature in the Mercury Afterglow

A study has been made of the behavior of a plasma in which no new ions are found, as regards electron temperature and concentration, to determine the sources of the electron energy. Measurements were made with a movable probe in a stream of ionized mercury vapor passing out from an arc discharge. The velocity and vapor concentration were determined by stroboscopic measurements on moving striations produced by an impressed alternating voltage. The vapor concentration, expressed in pressure reduced to 0\ifmmode^\circ\else\textdegree\fi{}C, varied between 0.05 and 1.5 mm of mercury. The rate of cooling of the electrons was very rapid at first, but below 2500\ifmmode^\circ\else\textdegree\fi{}K this rate decreased rapidly. Finally the electron temperature reached a constant value which was several hundred degrees above that of the vapor, the difference being proportional to the vapor concentration. The most reasonable source of energy necessary to keep up the electron temperature seems to be either the local recombination process, directly or through the metastable atoms formed, or the metastable atoms brought down the tube by the vapor stream.