Showing papers in "Plasma Physics in 1974"
TL;DR: In this paper, the spatial variation of the amplitude of electromagnetic radiation propagating into an inhomogeneous plasma is discussed in reference to nonlinear interaction of HCN laser radiation with plasmas and to experiments on r.f. heating of the ionosphere.
Abstract: The spatial variation of the amplitude of electromagnetic radiation propagating into an inhomogeneous plasma is discussed in reference to nonlinear interaction of HCN laser radiation with plasmas and to experiments on r.f. heating of the ionosphere. Previous results on the ordinary wave and on the extraordinary wave at normal incidence are reviewed with emphasis on the physical processes affecting the amplitude behaviour. New numerical results are obtained starting from an integral representation of the solution of the wave equation for waves in a cold, inhomogeneous, magnetized plasma slab. Resonance absorption is discussed for the cases of normal incidence in the presence of a magnetic field (the Budden problem) and oblique incidence in the absence of a magnetic field.
148 citations
TL;DR: In this article, a nonlinear theory for a quasi-monochromatic whistler wave packet interacting with the resonant particles in an inhomogeneous plasma is developed, where expressions for the distribution functions for the trapped and untrapped particles are obtained on the basis of generalized theorems of phase volume conservation.
Abstract: A nonlinear theory is developed for a quasi-monochromatic whistler wave packet interacting with the resonant particles in an inhomogeneous plasma. Expressions for the distribution functions for the trapped and untrapped particles are obtained on the basis of generalized theorems of phase volume conservation. A nonlinear equation is derived which describes the space-time evolution of the wave amplitude. The nonlinear growth (damping) rate at large distances from the front edge of the packet is shown to be determined by the difference between the average distribution functions of the trapped and untrapped resonant particles. Qualitative features of the nonlinear evolution of a wave packet in inhomogeneous plasma are investigated.
129 citations
TL;DR: In this paper, the density and temperature of an expanding laser-produced carbon plasma were measured over a large range of distances by several different methods, and it was shown that the electron temperature of the same element was found to decay with a dependence Tc varies as t-1 rather than the theoretical adiabatic Te varies as 2.
Abstract: The density and temperature of an expanding laser produced carbon plasma were measured over a large range of distances by several different methods. The density of an expanding element was found to have a time dependence ne varies as t-3. The electron temperature of the same element was found to decay with a dependence Tc varies as t-1 rather than the theoretical adiabatic Te varies as t-2. These results confirm theoretical predictions about the effect of three body recombination on the cooling of a laser produced plasma.
120 citations
TL;DR: In this article, preliminary results of experiments on ion collection by a cylindrical probe in a plasma at rest are presented and the influence of ion-neutral collisions on the value of the normalized ion current are shown.
Abstract: Some preliminary results of experiments on ion collection by a cylindrical probe in a plasma at rest are presented. The influence of ion-neutral collisions on the value of the normalized ion current are shown.
85 citations
TL;DR: In this paper, the density of inductively excited low pressure h.f. plasmas has been measured as a function of a small transverse static magnetic field for various levels of the H.F. power applied to the discharge.
Abstract: The density of inductively excited low pressure h.f. plasmas has been measured as a function of a small transverse static magnetic field for various levels of the h.f. power applied to the discharge. Evidence is given for the plasma excitation by the zero and first order electron cyclotron wave resonance. Characteristic differences between the results at low and high h.f. powers are discussed with a simple model of the power absorption by the plasma electrons.
85 citations
TL;DR: In this article, a broadening effect of finite orbit size on the profile of alpha-particle density, and hence of the energy transferred to the thermal plasma, was evaluated, and the maximum orbit width was found to be 1.64 R (2q rho /R)2/3, instead of epsilon 1/2 rho theta as predicted by the small rhotheta analysis.
Abstract: An appreciable fraction of the alpha -particles produced by fusion in next generation Tokamaks or in a reactor, will be trapped in the toroidal magnetic field. The radial excursion of their orbits will exceed the width of the production profile. The broadening effect of finite orbit size on the profile of alpha -particle density, and hence of the energy transferred to the thermal plasma, is evaluated. Existing orbit analysis is not valid in the conditions of interest ( epsilon 1/2 rho theta >r, where rho theta is the Larmor radius in the poloidal field) and the orbit characteristics must first be derived. The maximum orbit width is found to be 1.64 R (2q rho /R)2/3, instead of epsilon 1/2 rho theta as predicted by the small rho theta analysis. The broadening of the alpha -heating profile will have a modest effect on the temperature distribution.
74 citations
TL;DR: In this article, the energy loss rate of a fast ion to electrons as it slows down in a plasma of arbitrary electron degeneracy and for the equilibration of the ions and electrons in the plasma were derived.
Abstract: Expressions are derived for the energy loss rate of a fast ion to electrons as it slows down in a plasma of arbitrary electron degeneracy and for the equilibration of the ions and electrons in the plasma.
55 citations
TL;DR: In this paper, two types of interaction have been observed between two adjacent expanding plasmas, produced by laser irradiation, and the density and temperature of both the initial and interacting plamas have been measured, by photon scattering.
Abstract: Two types of interaction have been observed between two adjacent expanding plasmas, produced by laser irradiation. The density and temperature of both the initial and interacting plasmas have been measured, by photon scattering For interaction early in the expansion the results can be explained by classical ion-ion collisions, while for later interaction (lower density) electron-electron and electron-ion collisions provide an explanation.
43 citations
TL;DR: In this paper, a Korteweg-de Vries equation for a two component-plasma with cold ions (Ti=0 for both species) and isothermal electrons has been derived.
Abstract: A Korteweg-de Vries equation for a two component-plasma with cold ions (Ti=0 for both species) and isothermal electrons has been derived. The amplitude of the solitons is reduced drastically by a few percent of light ions and an initial perturbation breaks up into more solitons than in a one component plasma.
40 citations
TL;DR: In this paper, simple analytical expressions for calculating the electron-ion, free-free Gaunt factor for high electron temperatures (>or=1eV/k) and long wavelengths (>or = 0.1 mu m) are presented.
Abstract: Simple analytical expressions for calculating the electron-ion, free-free Gaunt factor for high electron temperatures (>or=1eV/k) and long wavelengths (>or=0.1 mu m) are presented. The values of the Gaunt factor are displayed in a graphical form for wavelengths in the range 0.1-100 mu m.
33 citations
TL;DR: Using a Korteweg-de Vries equation, the authors in this article studied the propagation of ion acoustic solitary waves in a two ion species plasma. But their work focused on the dispersion relation between two acoustic branches with different phase velocities.
Abstract: Using a Korteweg-de Vries equation the author studies the propagation of ion acoustic solitary waves in a two ion species plasma. As the dispersion relation presents two acoustic branches with quite different phase velocities, two types of soliton can propagate: the slow one which is subsonic with respect to one ion mode and supersonic to the other, has greater amplitude and smaller width than the fast one.
TL;DR: In this paper, the interpretation of plasma ion temperature measurements obtained by energy analysis of the charge-exchange neutral atom flux from Tokamaks is refined through development of a Monte-Carlo computer code which simulates the charge exchange process in a three-dimensional, unmagnetized plasma having variable density and temperature parameters.
Abstract: The interpretation of plasma ion temperature measurements obtained by energy analysis of the charge-exchange neutral atom flux from Tokamaks is refined through development of a Monte-Carlo computer code which simulates the charge-exchange process in a three-dimensional, unmagnetized plasma having variable density and temperature parameters. Analysis of the code-generated neutral energy spectra shows that the apparent two-temperature distribution often observed experimentally can be solely a consequence of plasma density and temperature gradients. Furthermore, this diagnostic may underestimate the actual maximum plasma ion temperature in certain cases.
TL;DR: In this article, the authors present conclusive evidence of anomalous absorption of an intense RHCP wave at high magnetic fields omega ce/ omega > 1, where omega ce and omega are the electron cyclotron frequency and the frequency of the electromagnetic wave.
Abstract: The authors present conclusive evidence of anomalous absorption of an intense RHCP wave at high magnetic fields omega ce/ omega >1, where omega ce and omega are the electron cyclotron frequency and the frequency of the electromagnetic wave.
TL;DR: In this paper, an experiment is described in which torsional Alfven waves are excited in a magnetized, partially ionized plasma column, and measurements of the propagation and polarization of the wave field are compared with numerical solutions of the dispersion equation.
Abstract: An experiment is described in which torsional Alfven waves are excited in a magnetized, partially ionized plasma column. Measurements of the propagation and polarization of the wave field are compared with numerical solutions of the dispersion equation. With decreasing degree of ionization, collisional coupling of ions with neutrals leads to an increased Hall effect, which can be expressed in terms of an effective ion cyclotron frequency. Peaks in axial wave number and damping as well as a change in polarization are found at this frequency. Radial inhomogeneities of resistivity and plasma density lead to a radial variation in amplitude and phase of the wave field.
TL;DR: In this paper, a generalization of the conventional diagrammatic technique to include the effects of the non-linear responses of the medium is presented, and a diagrammatic structure called multiple-photon vertices is introduced.
Abstract: The theory reduces to that for a classical collisionless plasma in the classical limit and to conventional quantum electrodynamics in vacuo. The generalization involves two stages. The first is the use of quantum electrodynamics to calculate the linear and non-linear responses of an electron gas. Explicit expressions are derived for the linear response in a static magnetic field, and for the lowest order non-linear response in the absence of a static magnetic field. The second stage involves a generalization of the conventional diagrammatic technique to include the effects of the non-linear responses of the medium. Additional diagrammatic structures called multiple-photon vertices are introduced. Rules are given for drawing the generalized diagrams and for writing down the associated amplitudes. Illustrative examples are given.
TL;DR: In this article, the spectrum of scattered ruby laser light due to collective electron motion has been used to measure the ion temperature in the dense plasma focus over a range of operating conditions, the highest values being obtained on only a few discharges in pure deuterium.
Abstract: The spectrum of scattered ruby laser light due to collective electron motion has been used to measure the ion temperature in the dense plasma focus Over a range of operating conditions the deuterium temperature in the dense pinch is between 07 and 3 keV, the highest values being obtained on only a few discharges in pure deuterium Interpretation of the scattered light in terms of a near-thermal plasma is favoured for the dense pinch for two reasons Firstly, the electron parameters derived from the scattered spectrum are in agreement with other independent measurements and secondly, the contribution to the spectrum by rare gas ions in the plasma can be quantitatively accounted for
TL;DR: In this paper, the role of thermal conduction in modifying the characteristics of steady state deflagration structures in laser-solid target interaction is investigated, and it is found that even in the case where the thermal convection is small, the properties of the flow must be modified to include heat transfer to the expansion fan, and two dimensional gas flow effects.
Abstract: The role of thermal conduction in modifying the characteristics of steady state deflagration structures in laser-solid target interaction is investigated. It is found that even in the case where the thermal conduction is small, the properties of the flow must be modified to include heat transfer to the expansion fan, and two dimensional gas flow effects. In the case of the thick thermal structure modified scaling laws must be used.
TL;DR: In this paper, a type of discharge is described for which the resonant operating process gives an r.f. electric field in the plasma intense enough that the oscillation amplitude of the electron in that field is equal to or larger than the electron Debye length.
Abstract: A type of r.f. discharge is described for which the resonant operating process gives an r.f. electric field in the plasma intense enough that the oscillation amplitude of the electron in that field is equal to or larger than the electron Debye length. This meets the conditions necessary to produce r.f. strong field instabilities, such as those predicted by Silin (1966). Moreover, the experimental set-up allows a precise measurement, in the strong field region, of the average electron frequency, fpe, and it is thus possible to know the ratio fpe/f0, (f0 is the external r.f. field frequency) which plays an essential role in the study of electron parametric phenomena. Lastly, this plasma possesses an extremely low level of electron density fluctuation ( delta fpe/fpe approximately=10-5) which enables one to study under the best of conditions the various instabilities resulting from electron parametric interaction. This plasma is self-sustained over the Dipolar resonance or the Tonks-Dattner resonances (also known as main and secondary resonances) and new data concerning operation on such resonances are being presented here, for example: pressure influence (collisions), dielectric permittivity and coupling factor.
TL;DR: In this paper, the toroidal and poloidal coils of the closed containment means of the ATC were used to accelerate a radial toroidal column in an average ion-ion collision time or less.
Abstract: Method for fast radial toroidal plasma column acceleration in an average ion-ion collision time or less back and forth in the plane of the closed containment means of the ATC described in U.S. Pat. No. 3,702,163, irreversibly to heat the plasma column. In accordance with this invention, current is flowed through the toroidal and poloidal coil means of the ATC and these coils are distributed to provide an unbalanced biasing force on the toroidal, current carrying, plasma column by means of a shaped magnetic field having an unstable region between spaced apart stable regions. By modulating the shaped field the plasma column is pushed back and forth between the two stable regions. In another embodiment, the plasma current is modulated to the same end.
TL;DR: In this article, a background of hydrogen gas was introduced to permit charge neutralization as the electron beam transmits the cusp, and the results showed that a 10-20 kA pulsed beam of 350 keV and 60 nsec has produced circulating electron layers with diamagnetic fields on the mirror axis.
Abstract: Space charge effects were virtually eliminated by introducing a background of hydrogen gas to permit charge neutralization as the electron beam transmits the cusp. As a result, a 10-20 kA pulsed beam of 350 keV and 60 nsec has produced circulating electron layers with diamagnetic fields on the mirror axis up to 185 per cent of the vacuum field and lifetimes up to 9.5 mu sec. These electron rings exhibit characteristics very similar to those generated by perpendicular injection.
TL;DR: In the C-stellarator, the electron temperature range covered was greater than three orders of magnitude (0-1 eV) and the electron density range greater than five orders of degree (1*108 cm-3) as discussed by the authors.
Abstract: In the C-stellarator, the containment of many different types of plasma has been studied. They range from high current density, high plasma density ohmically heated plasmas which can be compared to the plasmas of the T-3 and TS Tokamaks down to tenuous cold plasmas which can be compared to those investigated in the Wendelstein II stellarator. The electron temperature range covered was greater than three orders of magnitude (0-1 eV
TL;DR: In this article, the yield of multiply charged ions from a steady-state Duoplasmatron ion source has been investigated, and it is shown that the attainable yield for highly charged ions is limited by the typical structure of the discharge itself and by instabilities in the ion source plasma.
Abstract: The yield of multiply charged ions from a steady-state Duoplasmatron ion source has been investigated. With some simplifying assumptions regarding the discharge plasma structure, one can calculate the density distribution of various charge states for a given feed material and main discharge parameters. The obtainable yields for highly charged ions can also be estimated. Such calculations have been made for the rare gases Ar, Kr and Xe, and these have been compared with experimental results. The comparisons show quite good agreement. It is shown that, besides technological limitations, the attainable yield for highly charged ions is limited by the typical structure of the discharge itself as well as by instabilities in the ion source plasma.
TL;DR: In this article, the validity of the similarity or self-similar model of laser plasma heating is examined and some criteria relating to the maximum radium of pellets to which it may be applied, are derived.
Abstract: The validity of the similarity or self-similar model of laser plasma heating is examined and some criteria relating to the maximum radium of pellets to which it may be applied, are derived. Numerical studies of the parametric variation of plasma parameters with laser variation are presented. It is found that substantially increased energies may be expected with CO2 lasers, compared with ND:glass.
TL;DR: In this paper, the dispersion relation for whistler waves in a cylindrical plasma is calculated, and it is shown that for omega < omega ce/2, it is necessary to include collisions to account for the experimental results for the real part of dispersion relations.
Abstract: The group velocity of whistler wave packets was measured in an overdense cylindrical plasma. The phase velocity was measured using c.w. excitation. The waves are excited and received by small antennae which excite and detect an oscillating B field in the plasma. The dispersion relation for whistler waves in a cylindrical plasma is calculated. It is seen that for omega < omega ce/2, it is necessary to include collisions to account for the experimental results for the real part of the dispersion relation. In the limit of large collisions the dispersion relation goes to the plane wave result. It is found that there exists a range of plasma parameters for which two modes of the whistler waves are excited. It is also shown that whistler waves can be used in an interferometer system to measure plasma density.
TL;DR: In this article, the weak non-linear interaction of a discrete set of wave packets which propagate in a warm magneto-plasma is examined within the framework of the two fluid approximation, and the equations governing the behaviour of the slowly varying amplitudes of the waves are derived by applying standard perturbation theory to the combined system of Maxwell's equations and the fluid equations for each species of charged particles.
Abstract: The weak non-linear interaction of a discrete set of wave packets which propagate in a warm magneto-plasma is examined within the framework of the two fluid approximation. The equations governing the behaviour of the slowly varying amplitudes of the waves are derived by applying standard perturbation theory to the combined system of Maxwell's equations and the fluid equations for each species of charged particles and by using a multiple scale expansion in both space and time. It is shown that, for arbitrary directions of propagation, the interaction matrix elements possess the familiar symmetry properties with respect to interchanges of the wave vectors of a resonant triplet. It is also verified that the mean energy and momentum of each wave can be written as the product of the wave action with omega and k respectively and that the total wave energy and momentum are conserved during an interaction.
TL;DR: In this article, it was argued that Dupree's diffusion theory of random acceleration in turbulent plasmas is valid only in the same parameter range as in the 'classical' theory.
Abstract: It is argued that Dupree's diffusion theory of random acceleration in turbulent plasmas is valid only in the same parameter range as in the 'classical' theory.
TL;DR: In this article, the stability of ion acoustic waves propagating in a magnetized plasma containing an electron temperature gradient is investigated, and the dispersion relation is solved numerically for various electron-ion temperature ratios and electron temperature-gradient drift velocities.
Abstract: The stability of ion acoustic waves propagating in a magnetized plasma containing an electron temperature gradient is investigated. The dispersion relation is solved numerically for various electron-ion temperature ratios and electron temperature gradient drift velocities. Earlier predictions, based on analytic calculations for small temperature ratios and drift velocities, are confirmed and some new results are presented. In particular, it is shown that a temperature gradient is a more effective destabilizing agent than a simple drift between ions and electrons. Dispersion plots and neutral stability curves are given.
TL;DR: In this article, the propagation of laser radiation parallel to the magnetic field in a pinch plasma column has been studied and it is shown that waveguide type modes with no longitudinal dependence may be necessary because of radiation pressure considerations.
Abstract: Calculations are presented on the propagation of laser radiation parallel to the magnetic field in a pinch plasma column in reference to recent proposals for plasma heating. It is shown that waveguide type modes with no longitudinal dependence may be necessary because of radiation pressure considerations. The size of these modes is calculated self-consistently assuming classical plasma transport coefficients and inverse Bremsstrahlung absorption. In all cases of interest, the area occupied by the laser radiation is small compared to the cross sectional area of the plasma. The solutions are stable against self-focusing but unstable to a firehose instability at high radiation densities. From this viewpoint, a system in which the radiation can make many passes through the plasma is worse than a single pass system.
TL;DR: In this article, the Stokes-Ekman-Hartmann boundary layers and their physical implications were investigated in the presence of an infinite disk in an electrically conducting rotating fluid.
Abstract: A study is made of the unsteady hydromagnetic boundary layer flow induced by the torsional oscillations of an infinite disk in an electrically conducting rotating fluid in the presence of a uniform magnetic field. Information is obtained about: (i) the structure of the steady and the unsteady flow field; (ii) the development of the Stokes-Ekman-Hartmann boundary layers with their physical implications; (iii) the significant interaction of the electromagnetic and Coriolis forces; (iv) the hydromagnetic Ekman suction velocity and total transient time required for the establishment of the hydromagnetic boundary layers; and (v) the generation and propagation of a series of inertial oscillations and the diffused hydromagnetic waves. It is shown that the rapid attainment of the Stokes-Ekman-Hartmann boundary layers and the striking properties of the Ekman suction velocity play a distinctive role on the hydromagnetic spin-up process.
TL;DR: In this paper, the effects of these modes can be compared to those of electron-electron collisions, and the collisional diffusion which may be associated with these orbits can have an expression similar to that of the experimentally observed 'pseudoclassical' diffusion of electron thermal energy.
Abstract: Three typical electron populations are distinguished in a high temperature two dimensional toroidal plasma; those that carry current under the influence of an externally applied electric field, those that can circulate but do not carry appreciable current, and those that are trapped. Travelling modes, along the magnetic field lines, with frequencies larger than the transit frequency of thermal electrons can be excited when the distribution function of the first population tends to detach itself from that of trapped and weakly circulating electrons. The effects of these modes can be compared to those of electron-electron collisions. The trapped and barely circulating electrons are strongly affected by standing modes with frequencies of the order of the average trapped electron bounce frequency, and producing 'quasi-banana' orbits whose radial amplitudes are larger than those of the known 'bananas'. The collisional diffusion which may be associated with these orbits can have an expression similar to that of the experimentally observed 'pseudoclassical' diffusion of electron thermal energy.