Plasma In Thermal Equilibrium Research Articles

Continuous calibration of a vacuum ultraviolet system from 65 to 125 nm by a cascade arc and comparison with the calibrated line radiation of a hollow cathode

A high-power stationary helium cascade arc has been developed as a standard source for continuum radiation in the VUV spectral range from 65 to 125 nm. The calibration of the VUV system response was based on the calculated and measured continuum radiation of a 2-mmphi pure He arc. Diagnostics of the arc plasma in partial thermal equilibrium yielded the electron density and the temperature that were inserted in the calculations of the continuous radiation. The results were compared with the helium, argon, and krypton radiation lines of a high-current hollow cathode lamp. This lamp was built according to the construction drawings of a hollow cathode, which was calibrated by means of the electron synchrotron radiation at the Physikalisch Technische Bundesanstalt Berlin.

The Extreme‐Ultraviolet Emission of the Seyfert Galaxies Markarian 279, Markarian 478, and Ton S180

We present EUV light curves and spectra of three Seyfert galaxies. The data were obtained from EUVE observations of the galaxies Mrk 279, Mrk 478, and Ton S180. The variability in the light curves provides an upper limit to the size of the EUV-emitting region which excludes the broad-line region and diffuse intercloud regions as the source of this emission. The EUV spectra are all characterized by discrete line features; in the case of Mrk 478, we find the lines vary on timescales of less than 1 day. These results allow us to rule out various models proposed for Seyfert galaxies. Comparing these spectra in their rest frames, we find that several of these features appear at the same wavelengths. A composite EUV spectrum is produced from these redshift-corrected spectra. The most striking feature in the composite spectrum is an emission feature at ~79 A, which is also observed in the spectra of each of the individual galaxies. It is difficult to explain this feature by emission from a photoionized or collision-driven plasma in thermal equilibrium. We suggest this line feature may be the fluorescent transition of neutral Fe related to the 6.4 keV Kα emission that has frequently been observed in the X-ray spectra of Seyfert galaxies. If this interpretation is correct, this result imposes strong constraints on the distribution of warm material in these galaxies.

Energy and pressure densities of a hot quark-gluon plasma.

We calculate the energy and hydrostatic pressure densities of a hot quark-gluon plasma in thermal equilibrium through diagrammatic analyses of the statistical average, $\langle \Theta_{\mu \nu} \rangle$, of the energy-momentum-tensor operator $\Theta_{\mu \nu}$. To leading order at high temperature, the energy density of the long wave length modes is consistently extracted by applying the hard-thermal-loop resummation scheme to the operator-inserted no-leg thermal amplitudes $\langle \Theta_{\mu \nu} \rangle$. We find that, for the long wave length gluons, the energy density, being positive, is tremendously enhanced as compared to the noninteracting case, while, for the quarks, no noticeable deviation from the noninteracting case is found.

Derivation of the screening effects in a plasma in statistical and thermal equilibrium.

A derivation of screening effects in a moderately dense equilibrated plasma, based on the methods of finite temperature field theory, demonstrates the limits of validity of the ``weak screening'' form. Because the systematics of the theory make it possible to unambiguously separate off the leading order ${\mathit{e}}^{3}$, there can be no effects that cancel screening. The static nature of the equilibrium removes questions connected with use of time-response methods for a steady-state problem. The derived screening potential approaches the Debye-Huckel potential at large separations, but is cut off by quantum effects at short distances; the inherent violations of self-consistency in classical derivations of the Debye-Huckel potential are absent. Applied to the conditions of the Sun's central region, screening corrections deviate only moderately from the classical, \ensuremath{\sim}15%. The partial degeneracy of electrons also presents only small effects beyond those accounted for by the appropriate population factors. Given the weak role of screening, the effect of the corrections on solar neutrino fluxes is, therefore, seen to be small.

Magnetohydrodynamic simulations of outflows from accretion disks

Magnetohydrodynamic simulations have been made of the formation of outflows from a Keplerian disk threaded by a magnetic field. The disk is treated as a boundary condition, where matter is ejected with Keplerian azimuthal speed and poloidal speed less than the slow magnetosonic velocity, and where boundary conditions on the magnetic field correspond to a highly conducting disk. Initially, the space above the disk, the corona, is filled with high specific entropy plasma in thermal equilibrium in the gravitational potential of the central object. The initial magnetic field is poloidal and is represented by a superposition of monopoles located below the plane of the disk. The rotation of the disk twists the initial poloidal magnetic field, and this twist propagates into the corona pushing and collimating matter into jetlike outflow in a cylindrical region. Matter outflowing from the disk flows and accelerates in the z-direction owing to both the magnetic and pressure gradient forces. The flow accelerates through the slow magnetosonic and Alfven surfaces and at larger distances through the fast magnetosonic surface. The flow velocity of the jet is approximately parallel to the z-axis, and the collimation results from the pinching force of the toroidal magnetic field. For a nonrotating disk no collimation is observed.

The Effects of Plasma Fluctuation in MHD Generators. Studies with a Numerical Turbulence Model.

The effects of the spatiotemporal inhomogeneity of a plasma in thermal equilibrium on the local and output characteristics of a Faraday-type MHD generator were investigated using numerically modeled turbulent velocity and temperature data. The conditions of Saha equilibrium in the range of the mean temperature level and the maximum turbulent frequency were given. The mean conductivity formula was also given as a function of the rms fluctuation. The average correlations between the electric field fluctuations and those of the conductivity in the mean Ohm's law were evaluated in terms of the mean electrical parameters. Rosa's G-factor was modified to include the spatiotemporal conductivity variance. It was shown that the one-dimensional anisotropic model somewhat underestimates the effective resistance of the turbulent MHD plasma with a two-dimensional anisotropy.

Effects of Plasma Fluctuation in MHD Generators Studies with Numerical Turbulence Model.

Effects of the spatiotemporal inhomogeneity of a plasma in thermal equilibrium on the local and output characteristics of a Faraday-type MHD generator were investigated using numerically modeled turbulence data of the temperature and the velocity. The conditions of Saha equilibrium in the range of the temperature level and the frequency were given. The mean conductivity formula was also given as a function of the rms fiuctuation. The average correlations between the electric field fluctuation and that of the conductivity in the mean Ohm's law were evaluated in terms of the mean electrical parameters. Rosa's G-factor was modified to include the spatiotemporal conductivity variance. It was shown that the 1D anisotropic model somewhat underestimates the effective plasma resistance of the turbulent MHD plasma with 2D anisotropy.

Thermal, nonthermal, and stimulated fluctuations of tokamak electron cyclotron radiation

Electron cyclotron radiation is the only blackbody level e.m. radiation which emerges from magnetically confined, fusion grade plasmas. Its power fluctuations and their space correlations carry information relevant to plasma transport studies. An overview is given of the properties of electron cyclotron emission fluctuations for a plasma in thermal equilibrium and when the fluctuations are enhanced by plasma turbulence or by modulated auxiliary heating.

Collective phenomena and instabilities of perturbative quantum gravity at non-zero temperature

The leading temperature corrections to the graviton self-energy at small momenta and at temperatures well below the Planck scale are calculated, and gauge invariance of the underlying effective action is verified, generalizing and correcting previous investigations which were restricted to the static limit. By this the full dispersion relations of a graviton plasma in thermal equilibrium are obtained, which comprise a spatially longitudinal, a spatially transverse, and a partially spatially trnasverse mode. These are characterized by a common plasma frequency ω 2 pl = 22/45 × 16 πG p ( p being the energy density α T 4 ) above which there are gravitational plasma waves and below which dynamical screening occurs. In the static case only the spatially transverse mode is shielded with screening mass m 2 2/9 × 16 πG p . Whereas the spatially longitudinal mode develops an imaginary mass m 2 J = −58/27 × 16 πG p , is the analogue of the classical Jeans instability. For spatial inhomogencities with wavelengths larger than 1/ m j exponentional anti-damping occurs in the spatially longitudinal mode, and for sufficiently large wavelengths also in the partially spatially transverse mode.

Spectroscopic Detection of Oxygen in Nitrogeneous Gas Mixtures

AbstractA pulsed high‐frequency discharge was used to excite a non‐LTE (local thermal equilibrium) plasma with a high specific power density sufficiently high to dissociate oxygen and gaseous oxides. If traces of hydrocarbons were present in the gas mixture, in the spectrum the Violet system of CN appeared with a long radiation decay time. The CN bands are excited preferentially by inelastic collisions with metastable nitrogen molecules (A3σ). These levels can be efficiently depopulated by competing impact with atomic oxygen. By measuring the radiation signal during the radiation decay a dynamic range of 6 was achieved for a variation of the oxygen content between 1 and 100 ppm.The measured radiation decay of the violet CN 0–0‐bands at 388 nm was simulated by a simple model of rate equations valid in the time region where diffusion processes may be neglected.

Alternative representation of the dielectric tensor for a relativistic magnetized plasma in thermal equilibrium

An alternative representation of the dielectric tensor εij(k, ω) for a relativistic magnetized plasma in thermal equilibrium is presented. This representation involves an infinite series expansion in powers of , as well as an asymptotic expansion for large Here ωc = eB0/mc is the nonrelativistic cyclotron frequency, k⊥ is the wavenumber perpendicular to the magnetic field B0êz, and α is the dimensionless parameter defined by α = mc2/KBT. The present work generalizes Shkarofsky's (1966) representation. Moreover, unlike Trubnikov's (1958) formal result, in which the k⊥ and kz dependences of εij(k, ω) are inexorably coupled, the present representation naturally separates the k⊥ and kz dependences of εij(k, ω). As an application, the general expression is simplified for the case of a weakly relativistic plasma, and the dispersion relation is obtained for electromagnetic waves, including first-order relativistic effects. The method developed in this paper can be used for other non-thermal distributions.

Thermal Instability in a Hot Plasma

AbstractThe nature of local thermal instability in static and dynamic radiating plasmas described by an equilibrium cooling function has been reexamined. Several new results have been found. In a plasma in both thermal and hydrostatic equilibrium, if the cooling function is not an explicit function of position, and does not display isentropic thermal instability (i.e. sound waves are thermally stable), then isobaric thermal instability by the Field criterion is present if and only if convective instability is present by the Schwarzschild criterion. In this case, thermal overstability does not occur. For the case of a dynamical plasma we present a very general Lagrangian equation for the development of nonradial thermal instability. In the limit of large cooling time to free-fall time ratio, the equation is solved analytically by WKBJ techniques. Results are directly applicable to cluster X-ray cooling flows. Such flows are surprisingly stable except for perturbation wavenumbers that are very nearly radial. We believe that the origin of cooling flow optical filaments is not to be found in linear thermal instability.

Macroscale implicit electromagnetic particle simulation of magnetized plasmas

An electromagnetic and multi-dimensional macroscale particle simulation code (MACROS) is presented which enables us a large time and spatial scale kinetic simulation of magnetized plasmas. Particle ions, finite mass electrons with the guiding-center approximation, and a complete set of Maxwell equations are employed. Implicit field particle coupled equations are derived in which a time-decentered (slightly backward) finite differential scheme is used to achieve stability for large time and spatial scales. It is shown analytically that the present simulation scheme suppresses high frequency electromagnetic waves and that it accurately reproduces low frequency waves in the plasma. These properties are verified by numerical examination of eigenmodes in a 2D thermal equilibrium plasma and by that of the kinetic Alfven wave.

Motion of charged particles in planetary magnetospheres with nonelectromagnetic forces

We derive expressions for the mirror point, the bounce period, the second adiabatic invariant, and the bounce‐averaged azimuthal drift velocity as functions of equatorial pitch angle for a charged particle in a dipole magnetic field in the presence of centrifugal, gravitational, and Coriolis forces. These expressions are evaluated numerically, and the results displayed graphically. We also evaluate the average azimuthal drift speed for a flux tube containing a thermal equilibrium plasma distribution.

Validity of the Boltzmann distribution under non-linear constraints

The Boltzmann distribution exp (- lambda Ei) for the occupancy pi of a fixed energy level Ei derives from a maximum entropy procedure under the constraint of energy conservation Sigma iEipi=U0. This constraint is linear in the pi. It is shown that the form of the distribution still holds when the energy levels Ei depend on the occupancies pi, provided that dU identical to Sigma iEidpi is a perfect differential so that energy is conserved. The energy constraint then becomes non-linear in the pi. Specific applications of this result are covered, in particular the Poisson-Boltzmann equation for the electrostatic potential in plasma in thermal equilibrium.

A model for ionization balance and L-shell spectroscopy of non-LTE plasmas

We have developed a model for calculating ionic charge-state distribution and level populations in steady-state nonlocal thermal equilibrium (non-LTE) plasmas. We use this normalize the relative populations for a single ionization stage so that we can compute spectral line intensities as functions of electron temperature and density. These relative populations are determined by the balance of three processes: collisional excitation, de-excitation, and radiative spontaneous emission. As an application of the model, we have computed spectral-line intensities for all the Δ n = transitions of nitrogen-, oxygen- and flourine-like argon ions, and we have used these results to analyze recent experiments.

X-ray spectrum of sigma Geminorum: an RS Canum Venaticorum type binary

The binary system σ Gem has been observed on three occasions during 1984 November 17–21 with the medium-energy and the low-energy detectors on the EXOSAT Observatory. Spectral analysis of the data obtained over the energy range of 0.05–6.0 keV shows evidence for a bimodal temperature distribution of emission measure in an optically thin thermal equilibrium plasma with one component |$\sim5\times {10}^{6}$| K and the other one of |$\sim40\times {10}^{6}$| K. It is found that the lower-temperature component is the dominant source of X-ray emission. The data are interpreted in terms of emission from two types of hot coronal loops with constant pressure on the surface of the visible red giant star in the binary. The two systems of coronal loops correspond to the two temperature plasma components measured. The observed variations in the luminosity of the system are probably due to the rotational effects on the smaller, cooler loops confined to certain regions on the surface of the late-type giant star.

Arc facility for investigating non-local thermal equilibrium plasmas

A high-pressure arc facility has been modified for computerized control and data acquisition to simplify measurements of non-local thermal equilibrium (non-LTE) plasmas. The instrumentation uses a 1-m monochrometer with programmable wavelength scanning system. Plasma self-absorption is determined via a concave back mirror and shutter. The raw data are corrected for absorption, zeroed, centered, and smoothed. The net line intensity is then determined and converted into the radial emission coefficient prior to feeding into LTE or non-LTE analysis programs. Sample graphs demonstrating the self-absorption correction technique and data reduction procedure are presented.

Self-excitation effect in the scattering of electromagnetic radiation in a strong magnetic field

It is pointed out that the electron scattering of incident electromagnetic radiation of frequency ω i includes also a component with the cyclotron frequency ω L . Except in the limit ω i ⪢ ω L , this “self-excited effect” modifies appreciably the cross section. The modified cross section for a classical non-relativistic electron is given in this paper for both a single electron and a cold plasma. The spectral distribution of electron scattering is discussed and the Thomson absorption coefficient of a magnetized thermal equilibrium plasma is obtained for some typical cases. The results obtained here may be relevant to astrophysical processes, such as the spectrum formation of x-ray pulsars.

Pre-equilibrium emission of lepton pairs from oscillating quark-antiquark plasma.

The production rates of lepton pairs from an oscillating qq-bar plasma are calculated and compared with those expected from a plasma in local thermal equilibrium and from the Drell-Yan mechanism. It is found that for a reasonable choice of the parameters of the model, the pre-equilibrium rate may dominate over the thermal and Drell-Yan rates for the dilepton mass > or =2 GeV.