bluuebunny/crossref_metadata_2025_split huggingface dataset:
Kinetic method of investigating oscillations and stability of inhomogeneous plasma in a helical magnetic field
Authors: Mikhailovskaya L.V. , Mikhailovsky A.B. 
Published: January 2011

A new method based on the use of the kinetic Vlasov equation is suggested to investigate oscillations and stability of inhomogeneous plasma in a helical magnetic field of cylindrical symmetry. A dielectric permeability tensor has been obtained for the plasma configuration mentioned. Exceeding the limits of hydrodynamics permits one to study oscillations with a wavelength of the order of the Larmor radius of the particles. In addition such an approach makes it possible to take into consideration interaction between the resonance particles and the wave thus permitting investigations of the "kinetic" mechanisms of oscillation buildup. These questions have also been discussed in an earlier article of one of the authors.
The advance that is achieved in the present work consists of consideration of the curvature and shear of the magnetic field lines. With consideration of these quantities equations have been obtained that make it possible to investigate the behaviour of drift waves that are unstable in the case of a magnetic field with straight and parallel lines, and also waves that have been discussed by Suydam. We discuss the effect of a buildup of convective perturbations with resonance electrons that is connected with their motion along the lines of force. Such an effect takes place when the hdyrodynamic instability of Suydam is stabilized because of the large Larmor radius of the ions. The buildup effect mentioned is analogous to the "residual-instability" effect but considerably stronger than the latter if plasma pressure is small compared to magnetic pressure. This effect exists if there is a temperature gradient.
It is shown that in a plasma that is in a gravitational field and confined by a straight magnetic field, an analogous effect of drift buildup of flute perturbations is possible
Plasma acceleration by electromagnetic and magnetostatic field gradients
Authors: Consoli Térenzio , Hall R.B. 
Published: January 2011

The movement of charged particles in electromagnetic and magnetostatic field gradients is examined. It is shown that when the orientation and amplitude of such gradients are suitably arranged, the mean force in relation to time acting on these particles remains constant in direction. Discussed are this mean force and, more generally, the validity of the theory of mean value in relation to time.
The results are applied to the case of a low-density plasma, and a brief description is given of four possible applications of a device based upon such forces: as injector, plasma propellant, vacuum pump and direct converter of thermal energy into u.h.f. electromagnetic energy. Orders of magnitude are stated. In two annexes, the authors determine the limits of validity of the theory based on mean value, and a comparison is made with an exact theory. The curves obtained are described and classified by analogue computer.
Acceleration of plasma electrons
Authors: Stefanovsky A. M. 
Published: January 2011

The author studied plasma electron acceleration in toroidal devices where electron beam equilibrium on the annular orbit is secured by image currents appearing in a metallic housing that covers the vacuum chamber. The initial plasma was created in a toroidal magnetic field with the aid of electron injection along the lines of force of that field and neutral gas ionization in the chamber. The first series of experiments showed that the overwhelming majority of plasma electrons do not accelerate after the creation of an electric field up to 150 V/cm; at the same time powerful oscillations are excited in the plasma. These oscillations appear as a result of the effect on the plasma, of a non-uniform electric field. The results obtained in this series of experiments are analogous to those obtained on plasma betatrons.
In the second series of experiments the accelerating electric field was created uniformly and simultaneously along the column of the preliminary plasma. Comparison of the plasma density obtained with the aid of a probe technique, and measurement of the currents that appeared in the plasma show that probably all plasma electrons are initially accelerated by the electric field. Subsequently, however, for reasons that are unclear so far, acceleration ceases and the plasma current becomes a purely ohmic current. Measurement of the x-ray energy that appeared in experiments with an accelerating field of 250 V/cm shows that the electron component of the plasma is, under these conditions, heated by a short electric field pulse (1.7 × 10−7 sec duration) to a temperature of 50 - 70 keV. It is assumed that these effects can be very significant for obtaining large accelerated currents in plasma betatrons. In a denser plasma, one does not succeed in accelerating the electrons to relativistic energies; however, the superposition of a strong electric field can be applied with success for heating the electron component of the plasma.
Plasma equilibrium in a toroidal chamber with a travelling magnetic field
Authors: Volkov T.F. 
Published: January 2011

The displacement was found of the center of a plasma column in a toroidal chamber that is maintained in equilibrium by the average pressure of the high-frequency travelling magnetic field H and the dc magnetic field ℋ of the longitudinal surface currents. The travelling hf magnetic field is created by passing ac currents with specially selected phases through the annular conductors enveloping the chamber. It is assumed that these conductors do not affect the distribution of the dc magnetic field, which is assumed to be the same as in a single ideally conducting toroid. The solution is performed in assuming that toroidality is small (expansion in powers with respect to 1/R; R is the large radius of the torus).
The conditions for detachment of the column from the chamber walls in a quasi-static regime, is evaluated in the following manner. Let a plasma column of radius α be in equilibrium in a cylindrical chamber of radius b (R = ∞) at a distance δ from the walls. If the column is bent into a torus, then for detachment of the plasma from the chamber walls it is necessary that δ be larger than the displacement of the center of the plasma column Δ (a,b) = b – δ. The condition for detachment, δ > Δ (b – δ, b), limits β, the ratio of plasma pressure to full magnetic-field pressure (time average of H plus ℋ).
In a concrete case that is close to the experiments described in ref. 1 (R=35 cm, b=4 cm, and 12 waves of the travelling magnetic field fill the length of the torus), the formula is

h = ℋa/Hb is the ratio of x at the surface of the plasma column to H near the current conductors (on the surface of the chamber). From this formula it follows that for large longitudinal currents (h
2 > 0.49), detachment is impossible. From table I we can find the maxima of β for which, with preset h
2, a column can exist that is detached from the chamber walls. As is seen from this table, the conditions for detachment are very stringent.
Longitudinal dielectric constant of the classical plasma — I
Authors: Coste J. 
Published: January 2011

Starting from the work of Guernsey on the system of the two first equations of the BBGYK hierarchy, we show that an approximate solution of these equations may be found in the limit of high frequency or short wave length, and we derive general expressions for the longitudinal dielectric constant ε (k, ω) of the plasma. Limiting cases are considered: zero frequency [equilibrium quantities are derived from ε (k, 0)]; and frequencies much higher than the inverse relaxation time.
Longitudinal dielectric constant of the classical plasma — II
Authors: Coste J. 
Published: January 2011

We study the contribution of electron-electron correlations to ε (k, ω), by considering the case of a one component plasma. This contribution is compared to that due to the electron-ion correlations. A resonance effect is found at ω = 2 ωp. From ε (k, ωp) we derive a formula for the damping of the plasma oscillations.
Normal modes of plasma oscillation
Authors: Trocheris Michel 
Published: January 2011

The present paper is concerned with the well-known problem of electrostatic waves in a uniform collisionless plasma, in the linearized approximation. Although much work has already been done on this problem, a number of questions still arise. In particular a slightly unstable wave corresponds to an exact normal mode solution, whereas a slightly damped wave has a much more limited meaning: it is encountered by solving the equations with initial conditions in the manner first introduced by Landau.
In this paper a new type of normal mode is introduced which can represent damped waves as well as unstable ones, thus preserving the continuity between both kinds of waves. This is possible by considering the distribution function as a linear functional, or as an analytic function defined for complex values of the velocity. A complete system of such normal modes is formed. The spectrum consists of discrete eigenvalues corresponding to waves, either growing or damped, together with a continuum that may be chosen to have an imaginary part such that it corresponds to rapidly damped transients. An expansion formula is derived and the expansion given by Van Kampen and Case is recovered as a special case. This expansion is used to solve the equation for the distribution function and the relation to the solution by Laplace transformation is discussed.
Interaction of fast plasmoids with magnetic field barriers
Authors: Chwaszczewski S. 
Published: January 2011

A useful way of obtaining more accurate information about the processes that occur when fast plasmoids are trapped in magnetic traps is to investigate the interaction of the fast plasmoids with the barriers of magnetic fields that are constant or variable in time. The results obtained may be valuable in helping to clarify questions concerning the acceleration of plasmoids by variable magnetic fields and to explain some of the processes involved in penetration of the magnetic field by the plasma. To investigate the effects of the interaction between fast plasmoids and magnetic field barriers a coaxial plasma gun of the Marshall type was constructed. When the optimum conditions for operating the gun had been established plasmoids with a speed of 1.3 × 107 cm/s and an initial density of 2.5 × 1013 ion pairs per cma were obtained.
During investigation of plasmoid interaction with the barrier of a constant magnetic field, compression of the plasma was observed at low field intensities. At high magnetic field intensities the density of the plasmoids penetrating the barrier decreased until the plasma was completely reflected by the barrier. Using the model of a collisionless plasma, equations were obtained for the distribution of electromagnetic fields along the radius of a plasmoid passing through the barrier. By comparing the solution of this equation with the measured diamagnetic signal the electron gas density in the plasmoid was determined; it was found to be in agreement with results obtained with a twin probe. The interaction of plasmoids with the barrier of a variable magnetic field is determined not only by the amplitude of the field intensity, but also by a whole set of interaction phases. New values characterizing these phases were introduced for convenience. The reflection, partial penetration and acceleration of the plasmoids was measured for different interaction parameters.
Plasma electric noise of a steady hf discharge in a magnetic field
Authors: Vdovin V.L. , Rusanov V.D. , Frank-Kamenetsky D.A. 
Published: January 2011

The plasma is produced by magneto-acoustic techniques in a glass tube situated in a constant magnetic field. The plasma flows out continuously along the axis into the measuring chamber at whose centre the magnetic field varies from 700 to 2500 Oe. A hydrogen plasma was studied at pressures of (5 to 1) × 10−3 Torr. The active high-frequency power put into the discharge was 4 kW. The temperature of the electrons varied from 4 to 10 eV, and the electron concentration at the centre of the chamber was 1 × 1010 to 4 × 1012 cm−3. The density of the plasma and the temperature of the electrons were determined mainly by electric probes. Further, the density and temperature of the electrons were checked by a microwave technique (for which the Fabry-Perot interferometer was used) as well as by optical methods.
In the range from 10 to 200 kHz, intensive (∼1 V) electric noise with first-harmonic frequencies of several tens of kHz was discovered and investigated by means of dual electric and capacitative and double capacitative probes. The relationship between this noise and the plasma parameters was studied, and discussed from the point of view of the “universal” plasma instability.
Convective and absolute instability
Authors: Dysthe K.B. 
Published: January 2011

Unstable systems characterized by linear partial differential equations with constant coefficients are considered. The question of convective or absolute instability has meaning only for a stated condition; then the Cauchy problem for the system is solved by Fourier and Laplace transforms. For one space dimension, we start from the solution which is written as a Laplace inversion integral, and evaluate it asymptotically (t→ ∞). For several space dimensions we start from a solution of the Cauchy problem that is written as a Fourier integral; this solution is evaluated asymptotically by the saddle point method. Six criteria distinguish between the two types of instabilities. The first is equivalent to the criterion found by Sturrock, and applies only to systems propagating in one space dimension. The fifth is more general because it applies to one or more space dimensions. The second and sixth give sufficient conditions for convective instability. The third and fourth give sufficient conditions for absolute instability.
The “bulk” of the growing wave is defined to be the part of it having the highest growth rate. The velocity associated with the bulk of the wave is calculated for unstable systems satisfying the stated condition. This velocity may be zero for an absolutely unstable system.
A simple model for the yield of excited hydrogen atoms as a function of gas target thickness
Authors: Berkner K.H. , Kay L. , Riviere A.C. 
Published: January 2011

A simple analytical model is presented to describe the variation in the yield of excited hydrogen atoms formed by charge exchange as a function of gas target thickness. The model enables the existence of a maximum in the yield and the size of the maximum to be predicted from a minimum of cross-section information. A prediction can also be made for the amount by which the gas target thickness can be reduced in going from the value required for optimum total atom yield to that required for optimum excited atom yield. Both the ratio m of the yield at the maximum to the yield under thick target conditions and the reduction in target thickness r can be expressed in terms of only two independent variables by neglecting certain small cross-sections. Values for m and r are presented as sets of curves on one diagram.
From available cross-section data, values for m between 1.0 and 1.5 are predicted for H2, He, Ne, Ar and Xe gases for energies between 25 and 75 keV. The only experimental values of m available are those for Ne, Na and Mg reported by Il'in et al. For Ne the model predicts a value of m of 1.0 at 25 keV which is in agreement with the experiment. Although values of m up to 10 were observed by Il'in et al. for Na and Mg, there is insufficient cross-section data available as yet for these materials for predictions to be made from the model.
Plasma instability in the electric field of an ion-cyclotron wave
Authors: Sizonenko V.L. , Stepanov K.N. 
Published: January 2011

The authors investigate the stability of a collisionless plasma in which the ions are moving relative to the electrons at right angles to the applied magnetic field, under the influence of the electric field of an ion-cyclotron wave, with a velocity u⃗⊥ that is less than or commensurate with the thermal velocity of the ions vi. They study the excitation of longitudinal electrostatic oscillations with frequency and growth rate significantly greater than the gyrofrequency of the ions, but significantly less than that of the electrons, and with a wavelength significantly less than that of the ion-cyclotron wave.
It is shown that, when the ion temperature Ti is significantly higher than the electron temperature Te. electron-acousticoscillations are excited in the plasma. The excitation of these oscillations by resonance ions is possible even when u⊥ ≪ vi. When Te ≫ Ti ion-acoustic oscillations are excited in the plasma, the build-up of these oscillations by the ions being the result of absorption by resonance electrons. When Te ⪆ Ti oscillations are excited if the velocity of the ion beam u⊥ is somewhat greater than the thermal velocity of the ions.
When Ti ≫ Te. the reactive effect of the oscillations causes the function representing resonance ion distribution in the beam direction to level off and form a plateau. When Te ≫ Ti the unstable ion-acoustic oscillations spread the resonance electron distribution function, which is equivalent to electron heating, and slow down the ion beam.
Status report on MHD electrical power generation–IAEA/ENEA International Liaison Group on MHD Electrical power generation
Authors: Lindley B. C. 
Published: January 2011

The present status of commercial large-scale MHD electrical power generation is reviewed in the light of information presented at the Third International Symposium on MHD Electrical Power Generation (Salzburg, 1966) and of subsequent developments. Research and development activities, and the state of evaluation of engineering and economic factors are assessed in respect of open-cycle MHD power plant, closed-cycle MHD power plant, and the associated electromagnet.
The MHD power generator is attractive in that energy is extracted directly from that of the flow of working fluid. The generator itself is of simple static construction, thus permitting high maximum cycle temperature, high specific power output and potentially much larger unit size than may ultimately be achievable with turbomachinety. In principle, these features should offer increased thermal efficiency and reduced capital cost compared with conventional plant.
In the ‘open-cycle’ MHD system electrical energy is extracted directly from the flow of a plasma formed by the seeded products of combustion of a hydrocarbon fuel. The ‘closed-cycle’ MHD system similarly employs a working fluid which may be a seeded inert gas (helium, neon, argon) or a pure alkali metal. Operation may be based on the gas turbine or Brayton cycle, or incorporate steam plant (for the lower range of temperature) based on the condensing or Rankine cycle. In the case of the open-cycle MHD system, installations are being constructed or already operating successfully with hundreds of MW thermal input and tens of MW electrical output, and substantial effort has been devoted to other aspects of the plant. It is concluded that a pilot-scale power station is technically feasible but that the economics of MHD steam plant are not fully established.
Research and development towards the closed-cycle MHD system is at an earlier stage, and there are fundamental aspects of plasma behaviour relating to instabilities and the feasibility of utilizing magnetically-induced non-equilibrium ionization which have to be resolved. Engineering and economic evaluation of system concepts requires attention. Closed-cycle systems operated on a condensing or Rankine cycle with liquid-metal MHD generators are also at an early stage of development. There is as yet insufficient information on the performance of various liquid acceleration schemes and MHD generators to allow assessment for commercial plant, although for special applications (e.g. space vehicle power systems) the concept is attractive.
Superconducting electromagnets are technically and economically necessary for MHD power systems which, in almost all respects, derive benefit from operation at higher magnetic fields. Field levels of 5 – 7 T are attainable at present, and there are good prospects for further development to large size and higher fields.
Dynamics of three-wave processes in plasmas
Authors: Fedorchenko V.D. , Muratov V.I. , Rutkevich B.N. 
Published: January 2011

Travelling waves with a frequency of the order of 109 c/s were excited in a plasma column and their non-linear interaction with the ionic sound waves (f = 104 c/s) was observed.
At various distances from the input the authors recorded combination spectra showing the dynamics of the processes involved: the travelling wave amplitude decreases and, at a distance of 29 cm from the input, falls to zero, its energy being redistributed to numerous satellites. The energy redistribution process is not periodic.
The characteristic wave interaction time is found to be short (τ ∼ 10−8 s), which indicates the efficiency of the process and enables conclusions to be drawn regarding the determinacy of the interacting wave phases (δω⋅τ ≪ 1).
Contribution to the theory of magnetic pumping of an inhomogeneous collisional plasma
Authors: Nemov V.V. , Stepanov K.N. 
Published: January 2011

The authors consider the heating, by magnetic pumping, of a radially non-uniform plasma cylinder of non-uni form radius located in a longitudinal, constant and uniform magnetic field B. An oscillating magnetic field having the form of a travelling wave with phase velocity ω/k of the order of the ionic thermal velocity is produced by means of external azimuthal electric currents. The frequency of the oscillating field ω is significantly less than the reciprocal of the ion-ion collision time 1/τi, and the ion cyclotron frequency ωi, the plasma electrons are magnetized (the electron cyclotron frequency is considerably greater than the reciprocal of the electron-electron collision time), and the plasma pressure is significantly less than the magnetic pressure.Simple expressions are obtained for the energy absorbed per unit time by the plasma as a result of dissipative effects: ion viscosity and longitudinal electronic heat conduction (Joule losses play a minor role in magnetic pumping). Particular attention is paid to the case of acoustic resonance, where the inhomogeneous plasma contains a layer in which the velocity of sound is equal to the phase velocity of the excited wave. In this situation the absorption of energy by the plasma increases sharply and the increase in plasma temperature T is determined to within an order of magnitude by the relation dT/dt ∼ ωT(B∼/B)2, where B∼is the amplitude of the oscillating magnetic field at the axis.
Cusp containment and thermonuclear reactors
Authors: Spalding I.J. 
Published: January 2011

Existing theories of the cusp containment of quiescent plasma are reviewed. Some technical and economic requirements of any fusion reactor are then summarized and used to deduce the probable dimensions of open-ended high-β reactors. It is shown that such reactors must be long, pulsed, and of very high output power. Crucial physical problems are the microstability of the high-β plasma boundary and, to a lesser extent, problems associated with energy transport by hot electrons.
Assuming that these physical and technological problems are capable of solution, it is shown that mirror-symmetric versions of the hybrid-cusp discussed previously by Bickerton may have significant advantages over the simpler linear θ-pinch geometry.