Simple Plasma Model Research Articles

カスプ磁場を用いたイオンスラスターの放電プラズマ

Discharge plasmas in magnetic cusp ion thrusters were studied. To evaluate ion loss rates to the chamber wall, ion density distributions were measured by a Langmuir probe scanned along the wall surface. Comparisons of discharge perfomances were made for various electrode geometries, anode configurations and two different magnetic field strengths. A simple discharge plasma model based on the assumption of ionization by primary electrons was applied to investigate the cusp confinement for the wall and ring anode configurations.

Striations of the convective type and feedback in low-pressure mercury/noble-gas discharges

Experiments indicate that ionization-diffusion instabilities (striations) of the convective type, present in low-pressure mercury/noble-gas lamps, are generated by current fluctuations in the inhomogeneous part at the cathode end of the discharge. Self-excitation of striations is made possible by feedback via the electrical supply circuit of the lamp. An experimental boundary condition is found at the point of excitation. A simple plasma model, with an extension that takes feedback into account, fully describes the laser-like phenomenon of mode selection and the influence of the discharge length.

Alfvdén wave heating of a cylindrical plasma using axisymmetric waves. Part 1. MHD theory

MHD theory with the Hall term has been used to analyse the Alfvén resonance heating of cylindrical plasmas using axisymmetric waves excited by an antenna. An analytic expression for the antenna impedance has been derived for a simple plasma model and this is used to help interpret the computational results for small, medium and large plasmas. Compressional wave eigenmodes give large antenna resistances; however, the energy is deposited near the plasma surface. At a frequency just above each eigenfrequency, the Alfvén resonance damping is zero. Below the first eigenfrequency, the energy can be deposited near the plasma centre; however, the antenna resistance is fairly low except for medium size plasmas with a nearly constant central density. Ion cyclotron wave resonances are briefly discussed. Some general concepts relevant to the penetration of wave energy into large plasmas are presented.

Helical Equilibrium With Anisotropic Pressure and Mass Flow

A helical equilibrium equation with anisotropic pressure and mass flow is derived. A simple helical plasma model for high beta with highly anisotropic pressure (P|| ≫ P⊥) and small helicity is described. The effect of mass flow on a β-limitations which appears in this case is studied.

A study of compressional Alfvén waves in a toroidal plasma

A pair of loop antenna in a toroidal plasma device is found to excite compressional Alfvén waves in the frequency range of a few times the ion-cyclotron frequency. Two-dimensional profiles of the wave field and phase are obtained in a poloidal cross section as well as one-dimensional radial profiles. The main wave excited is found to have the fundamental poloidal mode number. However the contribution from higher poloidal modes increases at higher wave frequencies and plasma densities. Comparison with theoretical wave profiles shows deviation from a simple cylindrical plasma model.

Application of simple model theories to thermodynamic properties of liquid transition metals

The simple one-component plasma (OCP) model has been applied to thermodynamic properties of liquid 3d transition metals. For comparison, the results calculated by the hard-sphere (HS) model are also given. The electronic contribution to the entropy and heat capacity has been considered by a rectangular model of the density of states. In spite of the simplicity of the models the calculated values of the entropy, S, the specific heat at constant volume, CV, and the compressibility chi T, are in good agreement with experiment. This indicates that the OCP model, like the HS model, is well suited as a reference liquid for liquid transition metals.

The effects of parallel viscosity on stationary convection in plasmas

Stationary convection in a simple cylindrical plasma model driven interchange-unstable by an applied heat source is considered in the presence of large parallel ion viscosity. The nature of the spectrum and the cellular convective pattern at marginal stability are quite different from that obtained using only perpendicular ion viscosity.

Far-ultraviolet diffuse emission lines from the interstellar medium

view Abstract Citations (19) References (23) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Far-ultraviolet diffuse emission lines from the interstellar medium Paresce, F. ; Fossi, B. C. M. ; Landini, M. Abstract It is shown that the measurements of Feldman et al. (1981) of the diffuse emission lines of Si IV 1397 A, semiforbidden O IV 1406 A, semiforbidden N IV 1488 A, C IV 1549 A, and, possibly, semiforbidden O III 1663 A can be reconciled with a simple model of hot plasma in steady-state ionization equilibrium at T = 180,000 K. It is noted that the physical properties of this gas do not violate currently available observational constraints and that this component of the interstellar medium may have gone undetected until now. It is considered possible that this gas may be identified with that responsible for the EUV/soft X-ray background and possibly even with that responsible for the O VI absorption lines. The gas in the galactic halo highly clumped at T = 10 to the 4.9 power K cannot be the source of the observed emission if it is in approximate pressure equilibrium with its surroundings. Publication: The Astrophysical Journal Pub Date: March 1983 DOI: 10.1086/183988 Bibcode: 1983ApJ...266L.107P Keywords: Astronomical Models; Diffuse Radiation; Emission Spectra; Far Ultraviolet Radiation; Interstellar Gas; Ultraviolet Spectra; Forbidden Transitions; High Temperature Plasmas; Oxygen Spectra; Plasma Equilibrium; Astrophysics full text sources ADS |

OHTE: A Helical Pinch with Pitch Reversal

The OHTE configuration is obtained by surrounding a reversed field pinch (RFP) with a stellarator-like helical winding whose pitch is chosen to enhance field line pitch reversal. The helical coil current needed to form a separatrix boundary is calculated analytically for a simple plasma model, which gives results in close agreement with a numerical two-dimensional (2-D) MHD equilibrium code. Basic properties of the field line transform, which is predominantly in the axial or toroidal direction, are investigated. The 2-D equilibrium code is used to investigate the effects of current profiles and high beta, and the OHTE is compared with the RFP. These calculations show that the helical winding can significantly enlarge the parameter space for interchangestable finite-ß equilibria with pitch reversal while avoiding axial current reversal.

Mode coupling in a toroidal sharp-boundary plasma. I. Weak-coupling limit

The phenomenon of mode coupling in the discrete Alfven wave spectrum of ideal magnetohydrodynamics is studied using a simplified plasma model. It is shown that mode coupling occurs when a periodic modulation of the equilibrium magnetic field strength and curvature is introduced, either by toroidicity or by noncircularity of the cross-section. The existence of gaps in the frequency spectrum and the spatial localization of the eigenfunction as a result of mode coupling is analogous to the behavior of valence electrons in a one-dimensional crystal lattice.

An empirical formula for the (D,T) reaction rate parameter 〈σv〉

A simple analytic formula for the temperature dependence of the reaction rate 〈σv〉 of fusion processes in a Maxwellian DT plasma is given. Its accuracy is better than 2% between 10 and 100 keV and better than 10% between 2 an 10 keV as well as between 100 and 150 keV (if compared with the values calculated by Mileyet al.). The simplicity of the formula makes it particularly useful also for orientative evaluations of the performance of fusion experiments and reactors, based on simple plasma models. A few examples of applications of the formula are presented.

A model study of non-thermal effects in the plasma broadening of spectral lines

A simple model of a non-thermal RPA plasma is used to study possible collective resonances spectroscopically observable as satellites on spectral lines.

A hydrodynamic model for profile steepening at resonance absorption

The self-consistent modification of an inhomogeneous plasma density profile near the critical layer due to the ponderomotive force of an obliquely incident p-polarized electromagnetic wave is calculated within a simple hydrodynamic plasma model.

Charge separation and target voltages in laser-produced plasmas

Measurement of the voltages of isolated targets irradiated with 50-psec laser pulses show kilovolt target potentials existing for many nanoseconds. The amplitude of the voltage exceeds what is normally expected for a plasma pressure gradient by roughly an order of magnitude. The voltage amplitude and temporal characteristics are found to be dependent on the vacuum chamber dimensions. A simple one-dimensional plasma model explains the voltage characteristics through the existence of space-charge separation effects and leads to a measurement of the plasma temperature.

Angular distributions of x-ray line radiation from a laser-produced plasma

A method for measuring angular distributions of individual x-ray line intensities from laser-produced plasmas is described and applied to measure the strong angular dependence of lines from an aluminum plasma. The data are consistent with calculations made with a simple plasma model incorporating radiation reabsorption and transport in the plasma.

Mega-Gauss turbulence due to seeded composition fluctuations in dense plasma, and electron beam scattering

Fine scale variations in the chemical composition of a collision-dominated plasma give rise to corresponding spatial fluctuations in the electron density, which persist until being dispersed by diffusive or turbulent mixing. In the presence of a steep background temperature gradient these density fluctuations are expected to give rise to magnetic field fluctuations that reach the mega-Gauss range for temperatures of about a kilovolt. Using a simplified static plasma model, a spectrum is derived for the field fluctuations, together with a diffusion operator for the enhanced scattering of energetic particles in such a plasma. This phenomenon may be of interest in the design of targets for electron-beam driven fusion.

Use of intense relativistic electron beams to pump VUV lasers

Evidence is given to suggest that intense relativistic electron beams will find application as energy sources for pumping high-power vacuum ultraviolet lasers. A simple model of a stationary oxygen plasma was set up. When pulse heated, the plasma underwent a temperature evolution in close correspondence with measured values obtained in a plasma-heating experiment using a pulsed relativistic electron beam. In addition, a transient gain sufficient to produce amplified spontaneous emission (ASE) was calculated for the 3p→3s transitions in O III. The width of the gain curve was comparable to the width of experimentally measured uv laser pulses produced from an oxygen plasma having roughly the same density as in the plasma-heating experiment.

Comments on Field Line Resonances and Micropulsations

Summary Features and limitations of a simple plasma model exhibiting hydro-magnetic transverse mode field line resonances are discussed in relation to geomagnetic micropulsations.

Temperatur‐ und Konzentrationsprofile für ein nichtthermisches Sauerstoffplasmamodell

AbstractA simple cylinder symmetric oxygen plasma model is used to calculate the radial dependence of the gas temperature and ozon concentration for given electron temperature profiles.

A Vacuum Spark Discharge Source for Producing Highly Ionized Aluminum Lines in the Wavelength Region of 50-100 Å

A vacuum spark discharge source with aluminum electrodes is constructed to obtain highly ionized aluminum line spectra in the 50-100 Å region. It is similar to BRV sources in having a trigger electrode to initiate the discharge ; it differs from them in that the radiation from the discharge channel is observed in the radial direction. The highest ionization stage observed is Typical spectra are shown in a form of densitometer trace. A simple plasma model is assumed to discuss the possibility of obtaining more aluminum lines in the 50-100 Å region.