bluuebunny/crossref_metadata_2025 huggingface dataset:
Microwave-Plasma Interaction in a Thermally Ionized Plasma
Authors: Epstein Melvin
Published: December 2004

Equations have been formulated that govern the interaction between a plane transverse electromagnetic wave and the slightly ionized nonequilibrium gas flowing downstream of a shock wave. Under the assumption that the electromagnetic field is weak, the equations have been linearized and analytical solutions have been obtained. These solutions indicate that significant localized heating of the gas can be accomplished only for narrow ranges of the parameters of the problem. Calculations have been made for the increase in electron density and change in reflection coefficient. The results indicate that very small fields (e.g., 10 mW/cm2) can heat the electrons enough to significantly alter the reflection coefficient.
Interpretation of Observed Impurity Radiation in a Discharge of the C-Stellarator
Authors: Hinnov Einar
Published: December 2004

Measurements of absolute intensities of the resonance multiplets of oxygen ions in a typical discharge of the C-Stellarator are employed to deduce the ion concentrations as a function of time. The analysis of the data is based on an idealized model in which electron temperature and density are uniform both radially and axially. Electron temperatures are found from relative intensities of some of these multiplets, and compared with temperature computed from the electrical conductivity. Mean particle confinement times are deduced from the time behavior of the concentrations of highly ionized oxygen. From these confinement times, and the observed electron density changes, the particle influx rates are obtained. The total power loss by radiation is evaluated for the uniform model. The radiation by oxygen ions, which is explicitly nearly independent of temperature, and the ionization and heating of hydrogen influx, which is nearly proportional to temperature, are found to be the dominating mechanisms of power loss.
Mixed Sustained and Self-Sustained Discharge Mechanism in Shock-Ionized Argon
Authors: Dällenbach W.
Published: December 2004

The electrical discharge in dense plasmas such as those obtained in shock tube experiments is investigated theoretically. Assuming that the positive ion saturation current density is of the order of the positive ion random current density, it is shown that quite high current densities are possible in dense plasmas, without an electron emission at the cathode being required. For instance, current densities up to 1000 A/cm2 are possible in argon at a temperature of 15 000°K and a pressure of 1 atm. It is then shown that the positive ion mean free path is in general much larger than the positive space charge sheet near the cathode. Hence the positive ions may be accelerated by the cathode voltage drop. Since their accommodation coefficient is smaller than 1, they keep part of their kinetic energy after neutralization, and they additionally can heat up the plasma in the vicinity of the cathode. This self-sustained discharge mechanism, which represents a thermal breakdown of the plasma layer near the cathode, reduces the cathode voltage drop and limits the current density to a higher value.
Quantum Effects on the Conductivity of a Dense Plasma
Authors: Rand S.
Published: December 2004

The collective properties of a plasma, in its interaction with a radiation field, become important when the electron plasma frequency is comparable with, or exceeds, the radiation frequency. The particle interactions must properly be treated quantum mechanically when electron plasma wave phonon energies are of the order of, or greater than, average random electron energies. Both of these conditions may be satisfied for the system of optical or infrared radiation interacting with a dense plasma. Expressions for the high frequency conductivity and opacity are obtained for a dense, fully ionized plasma. It is found that, when the photon energy greatly exceeds the average random energy, and when the electron plasma frequency is much greater than the radiation frequency, then the free-free contribution to the opacity, ordinarily written without the inclusion of collective effects, is reduced by a factor of the order of ĒΩ3/ℏωp4, where Ē is the mean random electron energy in the plasma, Ω is the radiation angular frequency, ℏ is Planck's constant, and ωp is the electron plasma frequency.
Experimental Investigation of Radiation from an Argon Plasma
Authors: Tankin R. S. , Berry J. M.
Published: December 2004

A thermistor bolometer was used to measure the radiation from an argon plasma generated in a plasma torch and exhausted into the atmosphere. Pointwise radiation measurements along the centerline of the plasma jet yielded the axial distribution of radiative flux from the jet. Total radiation measurements revealed that up to 18% of the net power input to the plasma is radiated from the plasma jet. Temperature-radiation measurements showed the Kramers-Unsöld theory predicts the temperature dependence of radiation reasonably well.
Nonexistence of Quiescent Plasma States in Ion Propulsion
Authors: Derfler Heinrich
Published: December 2004

The problem of neutralizing an ion beam is analyzed within the framework of a one-dimensional collision-free theory. The character of steady-state solutions obtained depends upon the ratio between the mean thermal speed of the electrons and the ion velocity. When the ions are faster, excess electrons are returned to their source from a finite distance behind the electron emitter and the flow of charges is unidirectional (beam-like) further downstream. When the electrons are faster, a ``floating target'' must be postulated downstream to intercept electrons and ions at equal rates and to return excess electrons to the emitter. In this case the flow pattern of the electrons is ``plasma-like.'' Both beam-like and plasma-like states are found to be unstable with respect to small perturbations. Thus the plasma driving a space vehicle cannot be in a quiescent state.
Performance Studies with an Electrically Driven Shock Tube
Authors: Koopman David W.
Published: December 2004

Studies of an electrically driven shock tube employing a coaxial electrode configuration have been made to determine the nature of the shock-heated plasma and the suitability of such a shock tube as a source for quantitative spectroscopic measurements. Good agreement has been found between the flow velocity measured experimentally and the velocity predicted from a mathematical treatment of the acceleration process. Image converter camera photographs have shown that the flow is highly turbulent and irregular, in contrast to expected shock-wave behavior. A graphical procedure has been employed to calculate the conditions behind fast shock waves in a 75% He-25% Ne gas mixture at an initial pressure of 1 Torr. Time-resolved spectroscopic measurements of plasma conditions demonstrate that the temperature and density are about half those values calculated for the observed shock speed of 5.5 cm/μsec. The measured plasma conditions and the internal consistency of the data indicate that the gas can be described as being in quasithermodynamic equilibrium to within 30%. The irregular nature of the flow, however, restricts the usefulness of the device as a spectroscopic source.
Secular Behavior in an Analysis of Damped Standing Waves in a Gas
Authors: Morse T. F.
Published: December 2004

By considering multiple time scale behavior in the viscous damping of a one-dimensional wave, it has been shown how secularities (terms growing unbounded in time) present in the Hilbert solution of this problem may be eliminated. The method of time scales and the accompanying freedom to remove secular terms overcomes in part the major disadvantage of the Hilbert procedure which requires a periodic renormalization of the lowest order initial conditions. This method, which has proved most useful in nonequilibrium statistical mechanics, provides a link between the Hilbert and Chapman-Enskog treatment of a simple hydrodynamic problem.
Experiments on the Stability of Couette Motion with a Radial Thermal Gradient
Authors: Snyder H. A. , Karlsson S. K. F.
Published: December 2004

An experimental study has been made of the hydrodynamic stability of viscous flow between coaxial rotating cylinders with a superposed radial thermal gradient. For the data presented, the outer cylinder is at rest and the annulus is small. The axis of the cylinders is vertical; the fluid is water. There is a qualitative difference between the type of instability which first sets in when the thermal gradient is zero or nonzero: the secondary motion when the gradient is nonzero does not consist of toroidal Taylor cells. However, there is a transition to Taylor cells at a higher Taylor number. Free convection affects the results strongly. Quantitative data concerning the transition to Taylor cells are presented along with a qualitative description of the cells which first cause instability.
Azimuthal Plasmoid Motion in a Coaxial Source with Bz Bias
Authors: Wetstone David M. , Greber Isaac
Published: December 2004

Photographic evidence is presented for the presence of an azimuthal component of the plasmoid motion in a coaxial source of small aspect ratio when operated with an applied Bz field comparable in magnitude to the mean, self-induced Bθ field. The series of displaced images obtained suggests that the rotation is of the correct sense, and that restrikes of the source rotate in alternate directions with the current reversal in the source every half-wave. Photographs taken without bias field confirm the fact that the plasmoid does not form a continuous torus, and the theoretical consequences of this upon the simple hydromagnetic model are examined. This model is used also to derive an approximate equation of azimuthal motion which predicts an amount of rotation about three times larger than that observed. The amount of rotation does, nevertheless, scale with the bias field strength, as predicted by the model.
Unsteady Relative Extension of Incompressible Simple Fluids
Authors: Slattery John C.
Published: December 2004

Through a generalization of Coleman and Noll's discussion of steady extension we find a new class of flows which are dynamically possible in every incompressible simple fluid. An interesting aspect of this treat is that the two material functions which describe the behavior of the fluid are not the same as those found by Coleman and Noll, although they do become identical in the limit of steady-state behavior.
Scattering of Electromagnetic Waves by a Plasma Cylinder
Authors: Fejer J. A.
Published: December 2004

The scattering of an electromagnetic wave by a plasma cylinder is investigated. The problem of the homogeneous cylinder is solved analytically. Numerical solutions are obtained for two selected examples in which the plasma is cylindrically symmetrical but inhomogeneous. In the calculations, the thermal motion of the electrons is taken into account approximately by a scalar pressure term. The results of the calculations show that resonant scattering takes place at several frequencies. At the lowest resonant frequency the thermal motion of the electrons plays little part, and the plasma behaves essentially as a dielectric. Thermal motion plays a prominent part in the resonances which occur at the higher frequencies and which are caused by standing ``plasma waves'' (electron acoustic waves). These higher resonant frequencies are rather closely spaced (starting from just above the plasma frequency), if the plasma cylinder is homogeneous and its diameter is much greater than the Debye length. The separations between the resonant frequencies increase, however, if the electron density is taken to be substantially greater on the axis of the cylinder than at the boundary. The results of the present computations for such an inhomogeneous cylinder appear to be in qualitative agreement with data obtained from experiments on the resonant scattering of microwaves by a gas discharge column.
Analysis of Electromagnetic Wave Propagation Through Magnetoactive Plasmas
Authors: Gold Richard R.
Published: December 2004

A detailed analysis of electromagnetic wave propagation through a stratified magnetoactive plasma layer is presented. Exact solutions for the reflection and transmission coefficients are obtained for two general electron density distributions; kinked-trapezoid and exponential-homogeneous-exponential. Oblique incidence is considered with no magnetic field; a constant magnetic field applied normal to the layer is included for the case of normal incidence (ion cyclotron resonances are not considered). Numerical results are presented to illustrate the effect of the inhomogeneous plasma model on transmission. The asymptotic expansion of the solution for the kinked-trapezoid profile provides a simplified expression for calculation purposes when L/λ0 (ratio of slab width to free space wavelength) is larger than one. An infinite series solution is obtained in the final section based on an integral equation formulation of the problem including arbitrary variations in the properties of the stratified plasma (collision frequency as well as electron density). Relatively simple algebraic expressions for the reflection and transmission coefficients are derived when L/λ0 is small. Propagation across thin plasma slabs can be analyzed readily on this basis.
Test Particle Method in Kinetic Theory of a Plasma
Authors: Rostoker Norman
Published: December 2004

A test particle of coordinates X = (x, v) is surrounded by a shield cloud of field particles of coordinates X′ characterized by a conditional probability function P(X|X′t). A relationship has been found between this function, the one-particle function f(X, t) and the two-particle correlation function G(X, X′; t). It is G(X, X′;t)=f(Xt)P(X | X′t)+f(X′t)P(X′ | Xt)+n ∫ dX″ f(X″,t)P(X″ | Xt)P(X″ | X′t). The first two terms indicate that each of the two particles involved is a test particle as well as part of the shield cloud of the other particle. The last term corresponds to the two particles shielding a third particle. This relation has been established without solving explicitly for anything and has none of the usual restrictions such as spatial homogeneity, adiabatic time behavior, etc., usually necessary for obtaining explicit solutions. It is useful because the problem of kinetic theory is reduced to determining P which involves only the Vlasov equation. In addition, superposition principles for fluctuations, etc., are apparent at the outset.
Self-Consistent Method for Determining the Boundary Shape between a Plasma and a Magnetic Field
Authors: Baker John C. , Beard David B. , Young John C.
Published: December 2004

A calculational method of determining the boundary surface between a plasma and a magnetic field is described. The method consists of neglecting the curvature of the surface and approximating the magnetic field adjacent to the boundary by a sum of the field due to the local surface current and the plasma-independent magnetic field source. This field is used in the boundary equations to compute the boundary surface. The resulting surface is then used to compute the magnetic field due to the curvature of the surface and the computation of the boundary surface is repeated. Reiteration of the calculational steps is continued until a self-consistent solution is obtained in which the magnetic field resulting from the curvature of the previous surface is used to obtain a surface whose shape does not differ from the previous surface by more than the imprecision of the calculation of the magnetic field. The method is illustrated by application to three simple problems of (1) a line dipole immersed in a plasma exerting a constant pressure on the boundary, (2) a point dipole immersed in plasma exerting constant pressure, and (3) a line dipole in a plasma stream exerting a pressure in only one direction (parallel to the stream velocity).
Necessary and Sufficient Condition for the Stability of Plane Parallel Inviscid Flow
Authors: Rosenbluth Marshall N. , Simon Albert
Published: December 2004

Plane parallel flow between rigid plates of an incompressible inviscid fluid is considered. A necessary and sufficient condition for infinitesimal stability is derived in the special case where w″ has only a single zero and w′ > 0 where w(x) is the velocity profile between the plates. A general sufficient condition for instability is also obtained.
Shock Tube Studies of Radiative Transport in an Argon Plasma
Authors: Rutowski R. W. , Bershader D.
Published: December 2004

An experimental study was made of thermal transport at the stagnation point of a 1-in.-diam hemisphere-cylinder model immersed in a high enthalpy flow of shock-heated argon. Emphasis was placed on the separation of convective and radiative transport. Variation of operating parameters gave regimes in which (1) the heat transfer was almost wholly of the aerodynamic or convective type, or (2) both convective and radiative heat transfer had to be considered. Separate measurements of the total heat transfer and of the radiative component permitted separation of the former into convective and radiative parts. A limited comparison is made between the convective results and those obtained earlier for unionized argon. The radiative transport is compared with that obtained theoretically from the Kramers bremsstrahlung theory as applied to an argon plasma.
Interferometric Analysis of Axisymmetric Plasma Flow
Authors: Kahl G. D. , Wedemeyer E. H.
Published: December 2004

Experimental results of applying the method of two-wavelength, streak interferometry are given for the cylindrical, time-dependent flow of ionized argon produced by an exploding wire. Measurements from simultaneous streak interferograms at wavelengths 5460 and 4358 Å are used to determine contour charts of electron concentration and mass density of the shock-arc-heated argon plasma. Where thermal equilibrium can be assumed, values of velocity, pressure, and temperature can be deduced. The resulting temperatures agree well with those obtained from the Saha relation at the measured degree of ionization. The reduction equations and assumptions needed for the axisymmetric analysis are given. An estimate is made of the error in measured mass density caused by multiple ionization.
Supersonic Plasma Streams Seeded with Electronegative Gases
Authors: Carswell Allan I. , Cloutier Gilles G.
Published: December 2004

An experimental study of the properties of supersonic plasma streams which have been seeded with small amounts of an electronegative gas is described. It has been found that striking reductions of the electron and ion densities of the plasma can be achieved using sulfur hexafluoride (SF6) as the seed gas. The properties of seeded argon streams at pressures of 1 Torr and velocities of about Mach 2 have been studied using double-probe and microwave (9.2 Gc/sec) scattering techniques. The results show that when the SF6 is introduced with a concentration of only 5 × 10−4 relative to that of the argon in the stream, the plasma is quenched almost completely. Under these conditions the reflection of microwaves from the stream is reduced by 20 dB and the probe measurements show the presence of the ``hole'' cut in the plasma by the SF6. Measurements of seeding with argon, nitrogen, and oxygen in the argon streams are also discussed.
Dynamics of Vapor Bubbles in Binary Liquids with Spherically Symmetric Initial Conditions
Authors: Skinner L. A. , Bankoff S. G.
Published: December 2004

A technique is presented for determining the dynamics of vapor bubbles in binary liquids when the temperature and concentration fields are spherically symmetric. This is an extension of an earlier work [L. A. Skinner and S. G. Bankoff, Phys. Fluids 7, 1 (1964)], which employs the constant bubble pressure approximation, applicable when surface tension and inertial effects are negligible. The problem is solved in general form, and a specialized example is treated in detail.
Magnetoplasmadynamic Channel Flow and Energy Conversion with Hall Currents
Authors: Yen James T.
Published: December 2004

Several new complex parameters and several new real and complex functions are introduced for the first time. It is found that they are fundamental to this problem and hence to other problems involving Hall currents. Several conclusions on channel flow and energy conversion are obtained. In particular, it is shown under what conditions a mixed type generator can be more efficient than both the corresponding Hall current and ordinary-type generators. Moreover, it is shown that in a Hall current pump, it is unnecessary to require a zero net Hall current. With viscous effects, a suitable net Hall current and transverse loading combination may produce an optimum pumping.
Instability of an Alternating-Current Positive Column
Authors: Rugge Henry F. , Pyle Robert V.
Published: December 2004

The positive column of a glow discharge in a magnetic field is known to become macroscopically unstable at some critical magnetic field. The driving mechanism proposed by Kadomtsev and Nedospasov for the growth of a helical (m = 1) perturbation is such that the periodic reversal of the axial electric field at a frequency greater than a critical frequency would be expected to lead to stability. This critical frequency is expected to be approximately the e-folding rate. An experimental study has been made in dc and half-wave rectified-current discharges and in square and sinusoidal ac glow discharges in H2, D2, He, Ne, and Ar at frequencies as high as 70 kcps. Over a wide range of frequencies the half-wave rectified discharges yielded instabilities whose onset and helical nature duplicated those of the dc cases. However, the instability in the ac discharges was indeed suppressed as the frequency of electric field reversal was increased. The frequency-dependent suppression of the instability is compared with theoretical growth rates. The effect of including several m modes is calculated and good qualitative agreement is obtained with the Kadomtsev and Nedospasov model. However, better quantitative agreement is obtained when the Johnson and Jerde modification is employed.
Spatially Growing Electrostatic Turbulence
Authors: Drummond William E.
Published: December 2004

The nonlinear theory has been extended to spatially growing plasma oscillations in a bounded plasma, and it is shown that at large distances this leads to a stationary turbulent electrostatic spectrum. A novel feature appears in that the gradient of the longitudinal radiation pressure leads to a charge separation and consequently to a dc electrostatic field in the region in which the turbulence is growing.
Calculation of Gas Transport Properties and the Interaction of Argon Atoms
Authors: Barker J. A. , Fock W. , Smith F.
Published: December 2004

A method for calculating the collision integrals required for evaluating gas transport properties is described. The method is suitable for use with high-speed computers. Results are given for the Kihara spherical core potential function and for a potential function which Guggenheim and McGlashan derived for argon. The applicability of these potential functions to argon is tested by comparison with experimental viscosity and second virial coefficient data.
Oscillating Boundary Layer in Magnetohydrodynamics. I. Nonconducting Boundary
Authors: Caldwell Douglas R.
Published: December 2004

The hydromagnetic motion caused in an infinite fluid by an oscillating nonconducting boundary was studied theoretically. The results were confirmed experimentally by measurements of the damping of a torsional pendulum suspended in mercury in the presence of an axial magnetic field.
Interaction of Collisionless Plasma Streams with Transverse Magnetic Fields
Authors: Sellen J. M. , Bernstein W.
Published: December 2004

A collisionless field-free synthesized Cs+ plasma stream is impacted on the transverse magnetic field of a C-electromagnet. The configuration of a ``narrow'' beam is maintained as stream widths (∼4 cm) are small compared to the ion cyclotron radius. The interaction is observed to be unstable when the plasma penetrates or traverses a magnetic field in excess of ∼5 G. The instability is manifested by the appearance of both high (10–100 Mcps) and low (100 kcps) oscillations. It is believed that the instability arises from contrastreaming electron currents generated by a peaked potential structure in the boundary gradient region.
Stability of Potential Flow
Authors: Pierce John G.
Published: December 2004

An investigation is made of some questions pertaining to the stability of potential flow. A formalism due to Eckart is adapted to obtain equations for the perturbations of a known steady potential flow, in a coordinate system defined by the potential function and the stream function. Eigensolutions having a time dependence e−iωt are investigated for stability. It is shown that there exist no such stable solutions which are quadratically integrable in an unbounded space, or periodic in a closed space. A subclass of stable solutions is found, belonging to a continuous frequency spectrum. These are not quadratically integrable. The question of the existence of unstable but quadratically integrable solutions is not treated.
Annular Effect in Viscoelastic Fluids
Authors: Pipkin A. C.
Published: December 2004

In the oscillating motion of an incompressible viscoelastic fluid in a pipe, at high Reynolds number the root-mean-square axial velocity has its maximum value in a boundary layer at the wall of the tube. The elasticity of the fluid can make this annular effect much more pronounced than it is in the case of a Newtonian viscous fluid. The analysis is carried out for small-amplitude oscillations of a general viscoelastic fluid, and the exact solution for this case is compared with the solution obtained by the boundary-layer approximation. The solution in the case of slow motion of arbitrary amplitude is also considered, and it is shown that no annular effect occurs in this case.
Further Generalization of Onsager's Cascade Model for Turbulent Spectra
Authors: Corrsin Stanley
Published: December 2004

Onsager's conservative cascade model used to deduce the turbulent energy spectrum in the isotropic ``inertial range,'' is generalized in three different ways, with examples taken from the turbulent mixing problem. (a) Extension to a nonconservative cascade, mixing with a first-order isothermal chemical reaction, is presented more compactly than an earlier treatment and is applied to a new case. (b) Application to mixing at wavenumbers in the viscous range is indicated briefly. (c) Extension is made to a dual cascade, a model for turbulent mixing with a second-order isothermal reaction. The nonlinearity of the reaction causes spectral transfer.
Boundary-Layer Transition on a Cooled Rough Sphere in Hypersonic Flow
Authors: Kuethe Arnold M. , Ishii Takao , Amick James L.
Published: December 2004

Measurements are given of the combined effects of two-dimensional roughness and surface cooling on boundary layer transition at 45° from the stagnation point on a sphere in simulated hypersonic flow. With the roughness elements at 22.5° the combined effects of roughness and cooling are represented by a single functional relation between the transition length Reynolds number and the ratio between roughness height and the displacement thickness of the boundary layer at the roughness position. The measurements cover a range of ratios of surface-to-stagnation temperature of 0.5 to 1.0 and roughness heights of 1.8 × 10−4 to 4 × 10−3 in. Comparisons are made with measurements in incompressible flow and with one datum point in hypersonic flow.
Tail Shock Problem
Authors: Meyer R. E.
Published: December 2004

Attention is drawn to unresolved difficulties concerning the mechanism of tail shock formation behind bodies of revolution at supersonic and hypersonic flight speeds. In the limit of infinite Reynolds number, the flow near the neck of the wake is assumed to approach a locally conical field with vertex at the point on the axis where the shock starts. A detailed treatment is given for the case where the flow downstream of the shock is axial and of large Mach number M, so that the semivertex angle τ of the shock is small, but Mτ is not, and the shock is not weak. The problem then involves a small entropy parameter, and a uniform first-order approximation with respect to it is obtained. This may be the first purely analytical treatment of a conical shock that is not weak.

The gas is found to suffer a precompression, upstream of the shock, such that the density vanishes at the inner boundary of the stream. It is shown that this result must be expected to be independent of all but the one assumption that the gas impinges on the axis at a nonzero angle. Accordingly, tail shock formation in two-dimensional and axially symmetrical flows must be expected to differ in significant, still unknown ways.
Master Equation for Plasmas
Authors: McCune James E.
Published: December 2004

A straightforward derivation of the general kinetic equation describing the irreversible evolution of the N-momenta distribution function for a classical spatially homogeneous stable plasma (nrD3 ≫ 1) is given. Collective effects are included. This plasma master equation reduces to the weak-coupling master equation when collective effects are neglected. The results are given first in terms of a coupled pair of equations analogous to those obtained by Bogoliubov for the kinetic description of a plasma. The equation for the generalized correlations is then solved for stable plasma in terms of the N-momenta distribution function; the master equation then follows by substitution, and is shown to possess an H theorem. The conditions under which these results reduce to the kinetic equation of Balescu and Lenard, are discussed. The origins of irreversibility in plasmas are discussed in the light of this and other recent work, and the properties of the stationary solutions of the general kinetic equations are analyzed.
Magnetogasdynamic Boundary Conditions at a Conducting Wall
Authors: Luzzi T. E. , Gross R. A.
Published: December 2004

Velocity boundary conditions at a conducting wall have been developed for the continuum magnetogasdynamic equations. The wall is separated from the fully ionized plasma by a Langmuir type sheath. The effects of the sheath on the single fluid plasma boundary conditions are studied for the case where the particle gyro period is large compared to its flight time across the sheath. The effects of chemistry and heat transfer in the vicinity of the wall are ignored. For the case where the wall potential is greater than the plasma it is possible to have a slip velocity at the wall where no-slip would occur in an equivalent un-ionized gas flow. The magnetohydrodynamics equations have been solved with the above boundary conditions for the case of plasma flow between two parallel conducting plates held at a potential difference. The lower potential plate (cathode) is a thermionic current emitter. Depending upon the potential difference between the plates and the cathode thermionic emission current, the anode potential is either greater than that of the plasma and slip occurs or less than that of the plasma and no-slip occurs. Slip no-slip criteria are presented for the flow of plasma over many bodies, some of which are cathodes and the others anodes.
Oscillating Boundary Layer in Magnetohydrodynamics. II. Conducting Boundary
Authors: Caldwell Douglas R.
Published: December 2004

The generation of Alfvén waves by an oscillating, electrically conducting boundary was studied theoretically. Evidence concerning the validity of the calculations was obtained by measurements of the damping and period of a torsional pendulum suspended in mercury in the presence of an axial magnetic field. The electrical potential associated with the Alfvén waves was also measured.
Dynamics of Ionizing Shock Waves: Shocks in Transverse Magnetic Fields
Authors: Chu C. K.
Published: December 2004

Shock waves propagating into a nonionized neutral gas and ionizing it are considered. A transverse magnetic field is assumed. Using a simple ionization model, it is found that the electric field ahead of the shock may not be arbitrarily imposed, but is determined by the shock structure. This fact was already pointed out by Lyubimov; this paper extends Lyubimov's results and puts them on a more convincing mathematical basis. The piston problem is solved for these shocks; it is found that for a given ionization temperature these shocks are pure gas dynamic shocks at low piston speeds, and approach classical hydromagnetic perpendicular shocks at high piston speeds.
Magnetofluidmechanic Blast Waves in a Medium with Finite Electrical Conductivity
Authors: Lykoudis Paul S.
Published: December 2004

The classical theory of blast waves is extended in the case of an electrically conducting medium in the presence of a magnetic field. The plane (j = 0), cylindrical (j = 1) and spherical (j = 2) cases are discussed for a fluid possessing electrical conductivity varying with an appropriate power of temperature (say Tσ1), whereas the mass-density distribution of the medium in the undisturbed region and the imposed magnetic field are allowed to be inverse powers of the spatial coordinate r (say r−ω and r−b, respectively). For small magnetic Reynolds numbers it is found that similarity solutions exist provided the following relation is satisfied: 4b + 2σ1(1 + j − ω) = 3 + j + ω. The case of cylindrical symmetry with constant mass density and magnetic field parallel to the cylindrical wave is discussed in detail (ω = b = 0, σ1 = j = 1). Numerical results are provided for different values of the specific heat ratio. It is found that the magnetic field decelerates the fluid behind the shock wave, producing at the same time higher temperatures.
Plasma Rotation and Instability in the Θ-Pinch Due to Transverse Magnetic Fields
Authors: Thonemann Peter C. , Kolb Alan C.
Published: December 2004

Plasma rotation in a θ-pinch is analyzed theoretically on the basis of the mechanism proposed by Haines. The torque on the plasma is assumed to be due to the interaction of an axial Hall current with a weak transverse magnetic field component normal to the plasma axis. Such a transverse magnetic field is present when multipole fields of Ioffe type are used to prevent radial plasma drift. The Hall currents arise from the interaction of the main θ current with the transverse magnetic field. The problem is simplified by ignoring radial and axial plasma motion and assuming the plasma to be incompressible. The resistive decay of the plasma currents and the distortion of the initial transverse magnetic fields by the Hall currents are shown to be of primary importance in determining the characteristic growth time of rotation and the maximum rotational velocity. The condition for the appearance of flute instabilities as a result of plasma rotation is briefly discussed.
Beam-Temperature Effects on the Electrostatic Instability for an Electron Beam Penetrating a Plasma
Authors: Singhaus H. E.
Published: December 2004

The electrostatic instability of an infinite electron beam penetrating an infinite plasma is analyzed. The objective is to determine the effect of beam temperature upon the growth rate of the electrostatic waves (a Gaussian velocity distribution is assumed). In addition, the role of collisions within the plasma is explored. A conclusion of this study is that a high-temperature limit for the beam can be defined in terms of the plasma frequencies of the beam and of the plasma. At the high-temperature limit, the plasma collisions can quench the electrostatic instability; at lower temperatures, collisions tend to enhance the growth rate. The results presented here are based upon a numerical analysis of the usual dispersion equation that is obtained for this beam-plasma system. In addition to the numerical results, approximate analytic expressions for the growth rate are derived for a number of cases of interest.
Confinement of a Hot Electron Plasma in a Mirror Machine, DECA 1
Authors: Bariaud A. , Gravier R. , Korman M. , Luc H. , Renaud C. , Tachon J.
Published: December 2004

Plasma, produced by a hydrogenated titanium washer gun, was compressed between two pulsed magnetic mirrors (rise time : 150 μsec, decay time : 6 msec). For weak initial magnetic fields (below 150 G), and large compression ratios (above 100), the resulting plasma consists of very energetic electrons and of colder ions; it is confined during several milliseconds. Typically, with an initial field of 30 G antiparallel to a compression field of 10 kG, the compressed plasma has a diameter of 1.5 cm and a length equal to or less than 7 cm; the average hot electron density is (4 ± 2) × 1011 cm−3, with mean energy of 45 ± 10 keV; the density of the cold plasma, which might be present around the compressed plasma, is less than 1011 cm−3. Calculations show moreover that, in addition to the adiabatic heating, an important nonadiabatic acceleration occurs at the beginning of the compression. When the initial density is higher than 1013 cm−3, the energetic electrons do not appear. One observes, then, large radial leaks which might be caused by an instability. Such conditions correspond to a β which is higher than 1 to 3% for the compressed plasma.
Ohmic Heating in the B-1 Stellarator
Authors: Bernstein W. , Kranz A. Z.
Published: December 2004

A detailed comparison between experimental data and the predictions of ohmic heating theory is made over a wide range of axial magnetic confining field, electric heating field, and helium pressure. It is found that, in the early stages of the discharge, agreement between theory and experiment is good, and the predicted scaling laws are valid. However, experimentally it is found that it takes about 5 times longer to complete first ionization than predicted. Also, the current is seen to level off at a plateau at a time when theory predicts a continuous heating. These discrepancies are attributed to three energy sinks: cold neutral particles entering the discharge, runaway electrons leaving the discharge, and radiation from impurities. In addition, the electron density is observed to decrease during the length of the discharge (pump-out). For the early current plateau observed at low ratios of heating field to pressure, it appears that the plasma density is about 15% less at 18 000 gauss than at 27 000 gauss as a result of this pump-out. The hydromagnetic instability predicted by Kruskal and previously demonstrated to exist is given the physical characteristics of an increased rate of diffusion.
Interactions between First and Second Sound in Liquid Helium
Authors: Dessler A. J.
Published: December 2004

The reflection coefficient for a small-amplitude second sound wave reflected by a large-amplitude first sound wave front is derived. This type of reflection is unique in that the discontinuity (the first sound wave) travels faster than the wave being reflected. Hence, the discontinuity can overtake the second sound wave from behind. It is shown that the principal term in the reflection coefficient is due to the particle velocity associated with a pressure wave. This reflection coefficient is positive when the discontinuity overtakes the second sound wave from behind and negative when the discontinuity and the second sound wave are approaching one another head-on. The reflection coefficient for a small-amplitude first sound wave reflected by a large-amplitude second sound wave front is also derived.
Magnetohydrodynamic Flow in a Shock Tube
Authors: Mitchner M.
Published: December 2004

The effect of a transverse magnetic field on the motion of a perfectly conducting fluid in a shock tube is examined. A generalized form of the Riemann invariant for the continuous motion of such a fluid is combined with the conservation equations for a magnetohydrodynamic shock to obtain an exact description of the fluid motion in a shock tube in terms of arbitrary initial conditions. The fluids are assumed to have constant specific heat ratios.

Qualitatively, the effect of the magnetic field is equivalent to that of a pressure, but quantitatively the effect is always greater than merely the hydrodynamic pressure equivalent of the appropriate Maxwell stress. A magnetic field in the high-pressure region alone can produce shocks having Mach numbers for typical laboratory conditions, of the order of hundreds, and in general is in agreement with available experimental results. A magnetic field in the low-pressure region results in weaker, but higher velocity shocks.
Self-Diffusion in Liquids: Paraffin Hydrocarbons
Authors: McCall David W. , Douglass Dean C. , Anderson Ernest W.
Published: December 2004

The pressure dependence of the self-diffusion coefficients of several normal paraffin hydrocarbons and the isomers of hexane have been determined. In addition, the temperature dependence of self-diffusion coefficients has been measured for the isomers of hexane. Energies and volumes of activation have been calculated. With the exception of 2, 2-dimethyl butane, these parameters do not change significantly with branching in the isomers of hexane. The volumes of activation are about 10–20% of the molar volumes in all cases. Diffusion coefficients computed from a semiempirical modification of an equation derived by Longuet-Higgins and Pople are compared with the experimental results.
Method for Solving Fluid Flow Problems by Following the Motion of Energy Cells
Authors: Enig Julius W.
Published: December 2004

Numerical solutions have been obtained for one-dimensional fluid flow problems involving shock and rarefaction waves by fixing attention, for the first time, on the energy of the fluid and following the motion of constant energy cells, each of which contains a time-dependent quantity of mass. This is analogous to the usual method which consists of solving the Lagrangian hydrodynamic equations and following the motion of constant-mass cells, each of which contains a time-dependent amount of energy. The method has been applied to problems in which the total energy of the fluid is a constant. Solution by finite-difference techniques leads to a stability criterion which can be less restrictive than that obtained from the Lagrangian equations and hence give shorter computational times.
Analogy between the Rayleigh Problem and Flow behind the Shock Wave in Magnetohydrodynamics
Authors: Rosciszewski Jan
Published: December 2004

The flow behind a shock wave that propagates through a perpendicular magnetic field along a flat plate of high conductivity is analyzed under the assumption of small magnetic Prandtl number. Under such circumstances the regime of influence of magnetic diffusion is much thicker than the viscous boundary layer and the flow can be treated as essentially inviscid. On this basis it is shown that the problem becomes analogous to the Rayleigh problem, insofar as the velocity distribution along the wall is concerned, provided that the velocity of flow behind the shock wave is exactly equal to the Alfvén velocity.
Adiabatic Electron Fluid in the Presence of Strong Space-Charge Forces
Authors: Auer P. L.
Published: December 2004

We treat the case of an electron fluid with finite pressure embedded in a slowly varying axial magnetic field. Allowing for the presence of ions and accompanying space-charge forces, we find that variations in the resulting drift velocity vD alter the electron's precession frequency from the gyrofrequency Ω to a new frequency ω, with ω2 = Ω2 - Ω·(▿×vD). The precession orbit becomes distorted into an ellipse and the conventional adiabatic invariant is replaced with a new one. The fluid-dynamic consequences of these alterations are explored in the limit that the initial electron pressure is small compared to the initial magnetic pressure.
Prevalent Instability of Nonthermal Plasmas
Authors: Furth H. P.
Published: December 2004

In thermally anisotropic plasmas or sheet pinches, the zero-order counterstreaming or directed streaming of like particles gives rise to instability modes that correspond essentially to the formation of local first-order pinches within the plasma. The marginal stability criteria for all such modes can be interpreted in terms of Bennett's pinch condition. The range of examples discussed includes Weibel's thermally anisotropic hot-electron plasma instability in null field, which is generalized for hot ions and finite magnetic field, and which is applied to interpenetrating neutral plasma streams, to a spherical electrostatic plasma-containment scheme, and to the Astron thermonuclear experiment. The familiar ``mirror instability'' is shown to be another example of a ``pinch''-type mode. Sheet pinches with or without longitudinal magnetic field are generally unstable against tearing into subsidiary linear pinches.
Integral Equations for Distribution Functions in Fluids
Authors: Green H. S.
Published: December 2004

Starting from a chain of exact equations due to Mayer, integral equations are derived for the two-, three-, and four-particle distributions for a fluid mixture. An equation similar in form, but having some advantages over the hyper-netted chain equation, is obtained for the pair distribution function. This equation reduces in first approximation to the Percus-Yevick equation, but exhibits corrections to the latter depending on the three- and four-particle distribution functions. The solution of the equations for the three- and four-particle distribution functions is discussed, and it is found that a potential difficulty arises through the divergence of Neumann's expansion at sufficiently high densities.
Some Stabilized Plasma Experiments
Authors: Alexeff I. , Neidigh R. V.
Published: December 2004

Several combinations of magnetic cusps and mirrors are evaluated for their ability to contain cold plasma. Plasma noise, density, and decay time are measured. The plasma is considered stable if its loss rate is not greater than that permitted by multiple scattering. The cusp field with its annulus bent by adding axially parallel uniform field gave optimum containment. A plasma containing electrons at 25 to 130 keV temperature was found to be stable in a simple magnetic mirror configuration.
Collision Damping of Electron Plasma Waves
Authors: Rand S.
Published: December 2004

The damping of electron plasma waves, which results from electron-ion and electron-electron collisions, has been studied. A perturbation expansion about a self-consistent field is used. For long wavelengths, the principal contribution to the damping results from electron-ion collisions, with the contribution from electron-electron correlations smaller by a factor of the order (k/kD)2, where kD is the Debye wavenumber. Furthermore, in a high-temperature gas, it is found that the exchange contribution to electron-electron scatters is smaller than the direct contribution by a logarithmic factor.
Wave-Wave Scattering of Beam and Plasma Oscillations
Authors: Aamodt R. E. , Drummond W. E.
Published: December 2004

The spreading of the high-frequency electron plasma oscillation energy spectrum due to nonlinear interactions with a low-frequency beam mode is calculated for a homogeneous collisionless plasma with a large external magnetic field.
Electron-Density Measurements in an Electron Cyclotron Resonance Plasma
Authors: Shohet J. L.
Published: December 2004

Electron density in an electron cyclotron-heated plasma is determined by two methods. The first is by perturbation of the resonant frequency of fundamental modes of the cavity in which the plasma is contained. It is seen that for the TEL in (L > 0) class of modes, the resonant frequency increases, decreases and then increases as electron density is increased. The second method utilizes microwave transmission cutoff as the steady-state density of the plasma is such that the plasma frequency of the electrons exceeds the transmitted signal frequency.