摘要:

The attenuation of plane, right circular polarized electromagnetic waves propagating along an axial magnetic field into a thermal plasma is computed by an adaptation of Weibel's analytical and numerical results for nonmagnetic field cases.

ISSN:0031-9171    

DOI:10.1063/1.1692084

出版商:AIP    

年代:1968

数据来源: AIP

摘要:

The far‐field electromagnetic radiation produced when a field of supraluminous longitudinal plasma oscillations is incident on a localized inhomogeneity in the thermal plasma density is calculated. The plasma is assumed collisionless and is composed of stationary ions and thermal electrons. The calculation makes use of the thermal equilibrium spectrum of supraluminous waves (with phase velocities greater than the speed of light),which do not Landau damp. The generation and maintenance of this supraluminous spectrum is discussed elsewhere. Upon inserting numerical values for typical laboratory plasmas and also for a typical astrophysical radio source, such as the Crab nebula, it is demonstrated that the phenomenon is completely negligible in the laboratory but can be important in astrophysical systems.

ISSN:0031-9171    

DOI:10.1063/1.1692085

出版商:AIP    

年代:1968

数据来源: AIP

摘要:

Current chopping has been magnetically induced in low‐pressure (2 × 10−5− 5 × 10−3Torr) arcs carrying currents of 50‐200 A. The chopping was achieved in a time duration of 1‐10 &mgr; sec using a&thgr;‐pinch or an axially uniform magnetic field. Voltage spikes across the arc larger than 80 kV accompanied the chopping when an 8‐mH inductor was connected in series with the arc circuit. Irregular oscillations of frequencies higher than 10 MHz were detected during current chopping; the amplitude of the oscillations was proportional to the voltage spike. Other oscillations whose frequency range extended from 100‐200 kHz were detected, preceding and following the current chopping. x rays were emitted from the arc at current chopping whose flux depended on the voltage spike.

ISSN:0031-9171    

DOI:10.1063/1.1692086

出版商:AIP    

年代:1968

数据来源: AIP

摘要:

Observations are reported that by adding methane to the hydrogen or deuterium filling in the discharge tube of a theta pinch the absolute density at which it is possible to achieve breakdown in the preheater phase can be lowered. Plasma conditions have been investigated for a filling gas pressure of 0.8‐m Torr pure CH4or CD4, respectively, using light scattering and neutron emission. Measurements on impurity concentrations indicate that for low filling pressures and low absolute impurity concentrations, selective injection and loss of impurities to the walls during the preheater phase of a theta pinch may become important. Large errors can then arise in determining the concentration of elements with physically stable condensable forms (e.g., carbon and boron) when using the method involving the measurement of the intensity of an emitted spectral line as a function of added impurity concentration.

ISSN:0031-9171    

DOI:10.1063/1.1692087

出版商:AIP    

年代:1968

数据来源: AIP

摘要:

Faraday rotation measurements have been combined with Mach‐Zehnder interferometer measurements to yield the value of the internal magnetic fieldBiin the Scylla IV plasma as a function of time and radius. Since the Faraday rotation is proportional to∫ Bi(l)ne(l) dland the Mach‐Zehnder interferometer provides∫ ne(l) dl, the data give the average value of the internal magnetic fieldBi(r)which exists over the plasma lengthlat the radiusr. The measurements ofBi(r)are combined with those of the external magnetic fieldBeto determine the average plasma &bgr; as a function of radius,&bgr; = 1 − B2i(r)/B2e. The Faraday rotation measurement employs a 1.5‐mm diam beam of visible radiation (6328 A˚) from a He‐Ne gas laser as a plasma magnetic‐field probe and a calcite Wollaston prism as the polarization analyzer with silicon diode detectors. In the low‐pressure plasma regime (10‐25 mTorr) the &bgr; values in the central plasma‐core (∼5‐mm diameter) range in value between 0.9 and 1.0 with initial reversed bias magnetic fields and between 0.7 and 0.95 without bias fields. Radial profiles of &bgr; averaged over the plasma length have been obtained at various times during the discharge. A combination of &bgr;,n, andTein the simple pressure balance yields ion temperatures in the 2‐ 6‐keV region.

ISSN:0031-9171    

DOI:10.1063/1.1692088

出版商:AIP    

年代:1968

数据来源: AIP

摘要:

The spherical‐harmonic expansion of the Boltzmann equation is expanded in a power series in a small parameter, the average fraction of energy an electron loses per collision. The power‐series expansion permits an ordering in magnitude of the expansion coefficients of the distribution function, and thus indicates that many terms in the equations relating to the coefficients may be neglected.

ISSN:0031-9171    

DOI:10.1063/1.1692089

出版商:AIP    

年代:1968

数据来源: AIP

摘要:

The structure of a propagating current sheet in a linear pinch discharge in argon is examined with magnetic and electric probes, and interpreted from a magnetogasdynamic point of view. From an integration of thejzB&thgr;distributions it is deduced that the bulk of the initial mass fill of the chamber is radially accelerated to the current sheet velocity. Acceleration of ions in the sheet is partially accomplished by a radial electric field, which imparts about half of the necessary energy. The remaining energy is acquired through ajz+B&thgr;force applied to the ions, which are deflected axially as they pass through the sheet, and, therefore, conduct a large fraction of the axial current.

ISSN:0031-9171    

DOI:10.1063/1.1692090

出版商:AIP    

年代:1968

数据来源: AIP

摘要:

The gravitational instabilities of a system consisting of two homogeneous fluids with horizontal interface, in the presence of a uniform horizontal magnetic field, are investigated. The fluids are incompressible and have finite electrical conductivity and viscosity. The dispersion relation, which is obtained for the general case, is then specialized for a lower fluid of vanishing density, viscosity, and conductivity. In the limit of infinite conductivity in the upper fluid, the resulting dispersion relation corresponds to that previously obtained for a conducting fluid supported by a magnetic field against gravity. For finite conductivity in the upper fluid, this procedure avoids the difficulties involved as a result of diffusion across a supporting magnetic field. The effects of viscosity and resistivity on the Rayleigh‐Taylor modes are obtained. In addition, a resistive gravitational interchange instability is found, although magnetic shear is absent. It is further established that a small viscosity diminishes the growth rate of the resistive gravitational instability.

ISSN:0031-9171    

DOI:10.1063/1.1692091

出版商:AIP    

年代:1968

数据来源: AIP

摘要:

A one‐dimensional system of equations modeling the incompressible magnetohydrodynamic equations is proposed. Numerical experiments corresponding to the “turbulent dynamo” problem, in the form of a statistical initial‐value problem for the model system, are performed. Correlations, energy spectra, and other properties are examined at various times. The advantage of the model system is that no approximation need be made for the nonlinear “transfer” terms whose balance controls the outcome. The results of the experiments are that, for Reynolds numberRin the range 4‐20, dynamo action occurs in the model system whenever the magnetic Reynolds numberRmis greater than or equal toR. Dynamo action also occurs in the caseR = 20, Rm = 4, but fails to occur forR = 20, Rm = 0.2. In all cases where dynamo action occurs, the magnetic energy approaches the equipartition level, sometimes after first overshooting this level by a considerable amount.

ISSN:0031-9171    

DOI:10.1063/1.1692092

出版商:AIP    

年代:1968

数据来源: AIP

摘要:

Earlier conclusions about the nature of the turbulent energy budgets, the value of the inertial subrange spectral constant &agr;, and the turbulence Reynolds numberR&lgr;in a curved mixing layer are revised in view of the results of a recent investigation.

ISSN:0031-9171    

DOI:10.1063/1.1692093

出版商:AIP    

年代:1968

数据来源: AIP