Showing papers in "Plasma Physics in 1977"
TL;DR: In this paper, a simple theory of collisional attenuation, obtained by extension of the collisionless theory to the case of few collisions, predicts very well the dependence of the attenuation on the electron density, the electron collision frequency, and the geometry of the plasma column.
Abstract: Attenuation of a surface wave is studied experimentally in an unmagnetized cylindrical plasma column sustained by the wave itself. The losses connected with the plasma creation are negligible and the wave propagation is described by the relations for the linear regime. It is shown that a simple theory of collisional attenuation, obtained by extension of the collisionless theory to the case of few collisions, predicts very well the dependence of the attenuation on the electron density, the electron collision frequency, and the geometry of the plasma column.
106 citations
TL;DR: In this paper, the interaction of an electrostatic wave near the upper-hybrid resonance frequency with low-frequency electrostatic ion-cyclotron perturbations is considered.
Abstract: The interaction of an electrostatic wave near the upper-hybrid resonance frequency with low-frequency electrostatic ion-cyclotron perturbations is considered. It is shown that this interaction leads to the formation of near-sonic upper-hybrid envelope solitons.
61 citations
TL;DR: In this article, it was shown that random reconnections of magnetic field lines in a diffuse pinch can lead to the appearance of reversed axial field near the discharge tube wall, and it was suggested that the magnitude of the effect will depend on the degree to which current can be exchanged between adjacent field lines at a point of reconnection and on this basis a mathematical model was developed which described magnetic field configurations of the diffuse pinch which are intermediate between two extremes: the force-free paramagnetic model with no field reversal in the limit where the current does not follow the field at all
Abstract: It is shown that random reconnections of magnetic field lines in a diffuse pinch can lead to the appearance of reversed axial field near the discharge tube wall. It is suggested that the magnitude of the effect will depend on the degree to which current can be exchanged between adjacent field lines at a point of reconnection and on this basis a mathematical model is developed which describes magnetic field configurations of the diffuse pinch which are intermediate between two extremes: the force-free paramagnetic model with no field reversal in the limit where the current does not follow the field at all at a recombination point, and the Bessel function model in the limit where the current rigorously follows the field lines. An iterative procedure for the generation of intermediate configurations is described, and numerical results are presented and compared with experimental results from ZETA.
50 citations
TL;DR: In this paper, the amplitude, width and velocity variation of the solitons is studied, taking into account the ion thermal effects, and the results obtained are compared with those for plasmas with cold ions.
Abstract: Ion-acoustic waves in warm-ion plasma which includes some negative ions are studied using the properties of a modified Korteweg-de Vries equation. The equation, which describes the amplitude, width and velocity variation of the solitons is studied, taking into account the ion thermal effects. As in the case of a cold plasma, the warm negative ions also introduce a critical concentration at which the wave breaks up, which could play an important role in exploiting the ion-heating mechanism. The results obtained are compared with those for plasmas with cold ions.
43 citations
TL;DR: In this paper, a non-linear Schrodinger equation for Langmuir waves is derived by using a fluid model for the electrons, while both a fluid and a Vlasov formulation are considered for the ion dynamics.
Abstract: A non-linear Schrodinger equation for Langmuir waves is presented. The equation is derived by using a fluid model for the electrons, while both a fluid and a Vlasov formulation are considered for the ion dynamics. The two formulations lead to significant differences in the final results, especially in the expressions concerning the modulation instability of a plane Langmuir wave. When the Vlasov equation for the ions is applied, a Langmuir wave is modulationally unstable for arbitrary perturbations independent of the unperturbed wave amplitude, in contrast to what is found for fluid ions. A simple analogy with negative energy waves explaining the different features of the two cases is outlined.
42 citations
TL;DR: In this article, it was shown that the pinched electron diode may not be the most advantageous self-insulated geometry for a spherical focus, since the energy that produces the magnetic field is utilized inefficiently.
Abstract: Pulsed ion diodes magnetically insulated by their own feed currents can be treated in a manner similar to that used for applied field diodes. The self insulated diode has the advantages of easy construction and automatic confinement of the magnetic field to the acceleration gap. On the other hand, the energy that produces the magnetic field is utilized inefficiently. With models for the ion current density it is possible to calculate the optimum electrode shapes of ion diodes to produce a spherical focus. In this application it is shown that the pinched electron diode may not be the most advantageous self insulated geometry.
30 citations
TL;DR: In this article, it was shown that a whistler wave can parametrically decay into another whistler plus a kinetic Alfven wave, and that the parametric coupling occurs due to the electrostatic properties of the kinetic Alven wave.
Abstract: It is shown that a whistler wave can parametrically decay into another whistler wave plus a kinetic Alfven wave. The parametric coupling occurs due to the electrostatic properties of the kinetic Alfven wave. Corresponding growth rate and threshold condition are obtained.
29 citations
TL;DR: In this article, the singular eigenfunctions were used to obtain a solution to the problem of penetration of neutrals into a dense plasma with a realistic Maxwellian ion distribution.
Abstract: The method of singular eigenfunctions is used to obtain a solution to the problem of penetration of neutrals into a dense plasma with a realistic Maxwellian ion distribution. A general solution is obtained and explicit results given for models of the reflection processes at the wall. These include the neutral density distribution, the emergent neutral velocity distribution and the neutral particle and energy fluxes to the wall. The analytic results indicate the validity of the diffusion approximation and provide a boundary condition for such a treatment.
29 citations
TL;DR: In this paper, a kinetic equation for a multi-species plasma in an external uniform magnetic field is derived from the BBGKY hierarchy of equations, which generalizes the equation of Rostoker (1960), which assumes that the distribution function is independent of the azimuthal angle, and all previous results can be derived from it.
Abstract: A kinetic equation for a multi-species plasma in an external uniform magnetic field is derived from the BBGKY hierarchy of equations. The equation generalizes the equation of Rostoker (1960), which assumes that the distribution function is independent of the azimuthal angle, and all previous results can be derived from it. An additional advantage is that the collision integral is obtained in a form which is free from infinite sums of Bessel functions, and this greatly facilitates calculations based on it.
25 citations
TL;DR: In this article, the effects of a finite temperature ion beam traversing a plasma on the motion and characteristics of ion acoustic solitons were investigated for both ion species (beam and plasma) were adiabatic and for the case where one of the species was isothermal.
Abstract: The effects of a finite temperature ion beam traversing a plasma on the motion and characteristics of ion acoustic solitons were investigated. The soliton's width and amplitude as deduced from a Korteweg-de Vries equation were considered for the case when both ion species (beam and plasma) were adiabatic and for the case where one of the species was isothermal. The effects of changes in the temperature of the ion components on the characteristics of the solitons was also studied.
25 citations
TL;DR: In this article, low frequency self-oscillations are observed when an ion beam with a velocity near the ion acoustic velocity is injected into the plasma, which results from the fact that the system is axially bounded.
Abstract: In an ion beam-plasma system, low frequency self-oscillations are observed when an ion beam with a velocity near the ion acoustic velocity is injected into the plasma. This oscillation has a discrete spectral structure which results from the fact that the system is axially bounded. A real wave number for each discrete excited mode is determined by the bounded length. The self-oscillation frequency is approximately proportional to the wave number and to the ion beam velocity. These properties of the oscillation are quantitatively explained by the kinetic dispersion relation for the two stream ion-ion instability in the ion beam-plasma system.
TL;DR: In this paper, the authors measured the plasma focus current and found that only some pressure dependent fraction of the total current in the device flows at the focus region, and the correlation between this current and the neutron yield can be described as Y approximately I4.
Abstract: Using small magnetic probes, which were decoupled from the ground potential, the plasma focus current was measured. Only some-pressure dependent-fraction of the total current in the device flows at the focus region. The correlation between this current and the neutron yield can be described as Y approximately I4. The occurrence of m=0 instabilities in the focus plasma appears in the probe signal and is also correlated to the neutron yield. A comparison between MHD-calculations and the observed field structures is presented.
TL;DR: In this article, the possibility of using a plasma as the nonlinear medium of a parametric amplifier was examined and it was found that if the intensity of the pump beam is 1011 W/cm2 an experimentally realizable device could be made to amplify beams in the 11-16 mu m range with efficiencies limited only by the Manley-Rowe relations.
Abstract: The possibility of using a plasma as the nonlinear medium of a parametric amplifier is examined. In the proposed scheme a 10.6 mu m CO2 laser is used to produce the pump beam. It is found that if the intensity of the pump beam is 1011 W/cm2 an experimentally realizable device could be made to amplify beams in the 11-16 mu m range with efficiencies limited only by the Manley-Rowe relations.
TL;DR: In this article, a physical model and computer code were developed to study equilibria of strong proton rings and their behavior under an adiabatic increase in the external magnetic field.
Abstract: Recent calculations suggest the possibility of achieving a Lawson breakeven condition by the magnetic compression of proton rings to field reversal. This report describes a physical model and computer code RING developed to study equilibria of strong proton rings and their behavior under an adiabatic increase in the external magnetic field. Ring ion motion is followed using a volume-weighted finite-size particle-in-cell method. Because of the very short electron time scale, the electrons are simulated by a simple fluid model using Ohm's law. Quasineutrality, current neutralization in the r-z plane, cylindrical symmetry and a magneto-static model are assumed. Preliminary results indicate that (a) equilibria tend to be intermediate between the long layer and bicycle tire cases; and (b) compression past field reversal on the axis is possible within the framework of this model.
TL;DR: The NASA Lewis bumpy-torus superconducting magnet facility may be biased to positive or negative potentials approaching 50 kilovolts by applying direct-current voltages of the respective polarity to 12 or fewer of the midplane electrode rings as discussed by the authors.
Abstract: The toroidal ring of plasma contained in the NASA Lewis bumpy-torus superconducting magnet facility may be biased to positive or negative potentials approaching 50 kilovolts by applying direct-current voltages of the respective polarity to 12 or fewer of the midplane electrode rings. The electric fields which are responsible for heating the ions by E/B drift then point radially outward or inward. The low-frequency fluctuations below the ion cyclotron frequency appeared to be dominated by rotating spokes.
TL;DR: In this article, the envelope solitons are shown to be stable with respect to three-dimensional, long wavelength perturbations, and the authors explain apparent contradictions with previous work of other authors.
Abstract: Envelope solitons are shown to be stable with respect to three-dimensional, long wavelength perturbations. Apparent contradictions with previous work of other authors are explained.
TL;DR: In this paper, the spectral emissivity of a non-relativistic plasma of arbitrary density for frequencies above the electron cyclotron frequency is derived and a general formula is given which then is explicitly discussed for the case of thermal equilibrium.
Abstract: The spectral emissivity of a non-relativistic plasma of arbitrary density for frequencies above the electron cyclotron frequency is derived. A general formula is given which then is explicitly discussed for the case of thermal equilibrium. For emission perpendicular to the static magnetic field an analytic formula has been obtained. For arbitrary directions, the results are calculated numerically and given in graphical form. In the limit of vanishing electron density the usual results are recovered.
TL;DR: In this paper, it was shown that the kinetic equation for a plasma situated in a magnetic field, of a strength such that the ion Larmor radius is larger than the electron Debye length, has the form of a Fokker Planck equation in which the diffusion and friction coefficients can be derived from 'Rosenbluth potentials' in the usual manner.
Abstract: For pt.I see ibid., vol.19, p.237 (1977). It is shown that the kinetic equation for a plasma situated in a magnetic field, of a strength such that the ion Larmor radius is larger than the electron Debye length, has the form of a Fokker Planck equation in which the diffusion and friction coefficients can be derived from 'Rosenbluth potentials' in the usual manner. These 'magnetic Rosenbluth potentials' are however anisotropic, even if the plasma distribution functions is isotropic, because the magnetic field alters the dynamics of ion-electron collisions, and significantly enhances the duration of interaction of ions and electrons with no relative motion parallel to the magnetic field. The potentials are evaluated explicitly in the case of Maxwellian electrons.
TL;DR: In this paper, a resonant collective process can be excited in a plasma gradient which accelerates energetic particles into the higher density region of the higher-density region, and the process can then be used to accelerate the particles into higher density regions.
Abstract: A resonant collective process can be excited in a plasma gradient which accelerates energetic particles into the higher density region
TL;DR: In this article, the stability of the flute mode in a mirror-confined plasma of density n 0 is considered, and the instability potential is sampled at various azimuths around the plasma circumference.
Abstract: Axial feedback stabilization of the flute mode in a mirror-confined plasma of density n0 is considered. The instability is described using the usual low frequency slab model. The instability potential phi is sampled at various azimuths around the plasma circumference. The sampled potential is amplified, phase shifted in azimuth, and the resulting feedback voltage e is applied to a conducting endwall split into azimuthal segments. For typical mirror reactor conditions, stabilization is obtained for exactly 90 degrees azimuthal phase shift provided (e/ phi )(nx/n0) is greater than 7p2ai2/Rp2, where p is the azimuthal mode number, ai the ion Larmor radius, and Rp the plasma radius.
TL;DR: In this paper, it was shown that current conduction in a high current density Hall accelerator discharge is dominated in the early stages by a single density streamer (a spoke), and later by fast approximately 5 MHz fluctuations.
Abstract: Measurements are presented showing that current conduction in a high current density Hall accelerator discharge is dominated in the early stages by a single density streamer (a spoke), and later by fast approximately 5 MHz fluctuations. Linear electrothermal theory is extended and is used to identify these modes as an ionisation wave in a molecular plasma and a fast thermal mode in an atomic plasma respectively. A two dimensional time dependent fluid model of the plasma successfully describes further details of the early stages, and shows the effect of ion motion.
TL;DR: In this article, the magnetized Balescu-Lenard collision integral for a multi-species plasma in the form derived by Hassan and Watson (1976) is approximated by ignoring wave effects.
Abstract: The magnetized Balescu-Lenard collision integral for a multi-species plasma in the form derived by Hassan and Watson (1976) is approximated by ignoring wave effects. The resulting collision integral is put in Fokker-Planck form and most of the integrals occurring in the coefficients are performed analytically. The remaining integral is evaluated approximately in various limits for ion-electron, electron-electron and electron-ion interactions.
TL;DR: In this paper, the properties of cylindrical ion acoustic solitons which diverge from the exciter are compared with those of plane solITons, showing that the geometrical expansion of the wave fronts leads to a transition from a one-dimensional soliton to a dispersive oscillatory wave train even if the initial perturbation is a 1D soliton.
Abstract: The properties of cylindrical ion acoustic solitons which diverge from the exciter are compared with those of plane solitons. The geometrical expansion of the wave fronts leads to a transition of the solitons to a dispersive oscillatory wave train even if the initial perturbation is a one-dimensional soliton. In this transitional regime good agreement is observed between the experiment and numerical solutions of the cylindrical Korteweg-de Vries equation.
TL;DR: In this article, the effects of the magnitude and direction of the magnetic field on the plasma heating rate were studied numerically and a formula was derived for the power absorbed per unit volume of plasma in a uniform, static magnetic field.
Abstract: The excitation of electron plasma waves by interaction of two opposed electromagnetic waves in a magnetized plasma is examined. A beat frequency wave may be resonantly generated as either of two natural modes which have frequencies small compared to the sum frequency of the source waves. An analysis is based on Maxwell's equations and the electron-gas moment equations with the pressure tensor neglected. A formula is derived for the power absorbed per unit volume of plasma in a uniform, static magnetic field. The effects of the magnitude and direction of the magnetic field on the plasma heating rate are studied numerically.
TL;DR: In this paper, the drift motion of a collisionless plasma is measured in a curved magnetic field and a large drift is observed when the plasma is isolated from electric conductors, because a short-circuit path is formed through the conductors by the fast motion of electrons along the magnetic field.
Abstract: The drift motion of a collisionless plasma is measured in a curved magnetic field. A large drift is observed when the plasma is isolated from electric conductors. In a stationary state where the plasma is in contact with the conductors, the E*B drift is found to be very small, because a short-circuit path is formed through the conductors by the fast motion of electrons along the magnetic field.
TL;DR: In this article, the Korteweg-de Vries equation was used to model the reaction of a piston driver to a low-amplitude shock-like structure in a DP device.
Abstract: Plasma response to a piston driver has been modelled by the Korteweg-de Vries equation. The numerical shocklike solutions are evolving solitons similar to the asymptotic solutions of Gurevich and Pitaevski (1974). Quantitative experimental agreement is found with low-amplitude shocklike structures in the DP device.
TL;DR: In this paper, the spectrum of light scattered by a plasma in a magnetic field consists of a sequence of peaks if the scattering vector k is almost perpendicular to the magnetic field B. The angular location of this wedge can be determined by using a Fabry-Perot or a Michelson interferometer.
Abstract: The spectrum of light scattered by a plasma in a magnetic field consists of a sequence of peaks if the scattering vector k is almost perpendicular to the magnetic field B. Serious smearing of the peaks occurs when 2kve cos pi >or= omega ce where pi is the angle between k and B. Hence the scattered light will exhibit modulation only within a thin angular wedge. The angular location of this wedge can be determined by using a Fabry-Perot or a Michelson interferometer and from this direction of the magnetic field can be determined. A generalized treatment is presented to allow for the interpretation of experimental results from any light scattering arrangement or plasma field configuration. The limits imposed on this diagnostic technique, such as the laser beam divergence and field uniformity are also derived.
TL;DR: In this paper, the interaction of a high intensity relativistic electron beam with plasma was studied using a short pulsewidth electron beam source, where the beam was injected axially into a magnetized plasma column with density np=4*1011-1*1013 cm-3.
Abstract: The interaction of a high intensity relativistic electron beam with plasma is studied using a short pulsewidth electron beam source. The beam is injected axially into a magnetized plasma column with density np=4*1011-1*1013 cm-3. The beam current is completely neutralized by a 'reverse current' when the plasma density is sufficiently high. In a low density region decay of the reverse current appears, explained by enhanced collisions due to plasma instabilities. Though the pulsewidth is as short as 3 ns, the beam energy is efficiently transferred and the plasma is heated. Dependence of plasma energy increment upon initial plasma density and beam current are studied. As a result of the beam-plasma interaction, strong microwave emissions are observed at frequencies near electron cyclotron harmonics that last long after the termination of the beam, and the fundamental emissions are very weak. A possible explanation is to attribute the microwave emissions to electrostatic cyclotron harmonic wave instabilities excited in non-Maxwellian plasma heated by the electron beam and trapped in the magnetic field.
TL;DR: A theory of the generation and propagation of two and three dimensional magnetohydrodynamic surface waves due to an arbitrary as well as special oscillatory pressure distribution acting on the free surface of an inviscid electrically conducting fluid is presented in this paper.
Abstract: A theory of the generation and propagation of two and three dimensional magnetohydrodynamic surface waves due to an arbitrary as well as special oscillatory pressure distribution acting on the free surface of an inviscid electrically conducting fluid is presented. The unsteady solutions for two as well as three dimensional free surface elevation are obtained explicitly. The asymptotic behaviour of these solutions for large time and distance are determined to describe the qualitative and quantitative nature of the wave motions. The solutions consist of both the steady-state and the transient components. The latter is found to decay asymptotically for large time, and the steady-state is reached. Magnetohydrodynamic surface waves in deep and shallow fluid are dispersive in nature.
TL;DR: In this paper, a method for the construction of all solutions of the relativistic Vlasov equation that depend on one cartesian coordinate z and time t in the combination z-Vpt only with Vp>c was given.
Abstract: A method is given for the construction of all solutions of the relativistic Vlasov equation that depend on one cartesian coordinate z and time t in the combination z-Vpt only with Vp>c. These solutions represent non-linear electromagnetic waves in a relativistic plasma without static fields, which reduce for sufficiently small amplitudes to the longitudinal and transverse waves in a uniform plasma known from linear theory. Explicit expressions will be given for the influence of wave amplitude and plasma temperature on the coupling of longitudinal and transverse wave components, the dispersion relations of longitudinal and transverse waves and the modulation of plasma density and streaming velocity. The relevance of elliptically polarized transverse waves of this type to the description of pulsar waves is discussed.