Coaxial Discharge and Transverse Magnetic Field

The study deals with the effect of an applied transverse magnetic field on the dynamics and parameters of the focused and expanded plasma in a coaxial discharge. The experimental results were found with a 3 kJ Plasma focus device of a Mather geometry. The discharge takes place in hydrogen gas with base pressure of 0.5 Torr. The experiments are conducted with a 10 kV bank voltage, which corresponds to 100 kA peak discharge current with rise time 8 μs. Helmholtz magnetic coils are placed outside the expansions chamber to produce a transverse magnetic field with intensity 280 G perpendicular to the plasma expanded from the coaxial electrodes. The investigations have shown that the plasma flow along the expansion chamber axis is restricted when applying the externally transverse magnetic field and the maximum axial velocity of the expanded plasma is decreased by 33%. X-ray probe has been used to measure the focused plasma electron temperature (T_e). The experimental results and the calculations showed that T_e is decreased from 2.2 keV to 800 eV with the application of a transverse magnetic field. The expanded plasma electron temperature and density have been measured by an electric double probe, the results cleared that the expanded plasma electron temperature is decreased by 2.6 times while its density is increased by 9 times, when a transverse magnetic field is applied.     

On the possibility of natural formation of a transverse wave with a phase velocity lower than the velocity of light

The formation of a transverse wave with a phase velocity lower than the velocity of light, which can exist in an equilibrium plasma without a slow-wave structure in zero magnetic field, is described. It involves the transformation of a transverse wave with trapped electrons, traveling along the magnetic field, into a slow transverse wave after the removal of the magnetic field. During the evolution of the wave with trapped electrons, the magnetic induction decreases very slowly in the direction of the wave propagation. As a result, the velocity at which electrons are in resonant interaction with the wave increases; therefore, the electrons fall to the bottom of potential wells. Under the influence of the trapped electrons, the phase velocity of the wave decreases and becomes lower than the velocity of light. It becomes equal to the velocity at which the electrons are in resonance interaction with the wave at the instant when the magnetic field vanishes. It is demonstrated that a transverse wave with a velocity lower than the velocity of light can exist in an equilibrium plasma even after the magnetic field vanishes; in this case, the flow of trapped electrons serves as a slow-wave structure.     

Hot-Electron Magneto-Transport in InSb

The balance equations are used to investigate the hot electron magneto-transport in narrowgap semiconductor InSb at 77 K in crossed weak magnetic field and electric field. In the case of vanishing transverse velocity, the drift mobility and the Hall mobility are calculated and it is shown that the Hall factor in InSb at 77K is less than 1 and decreases with electric field. In the case of vanishing transverse electric field, the longitudinal velocity and the transverse velocity are calculated as a function of the magnetic field and the electric field. The effect of the magnetic field on the longitudinal velocity is different from that on the transverse velocity.     

Comments on “hydromagnetic slip flow with heat transfer in an inclined channel”

The hydromagnetic slip flow of a viscous incompressible and electrically conducting fluid through an inclined channel of rectangular cross section in the presence of a transverse magnetic field has been analysed. The walls of the channel are assumed to have prescribed temperatures and finite conductivities. The boundary conditions for both velocity and temperature are properly rectified. The expressions for the velocity, induced magnetic field and the temperature are obtained both analytically and numerically.     

Axial discharge stabilization using a rotating magnetic field

A new axial gas discharge stabilization technique is described. Thermal instabilities and discharge constrictions are suppressed through the use of a transverse rotating magnetic field. The enhanced plasma stability observed is a result of a transverse Lorentz force that deflects the plasma column off-axis. As the magnetic field rotates, the plasma sweeps across the tube cross-section at the angular velocity of the impressed field. A 25% increase in power loading has been achieved using the stabilization technique.     

Quasistationary magnetic field generated in a plasma by a whistler-mode radio pulse

It has been shown experimentally that a quasistationary magnetic field is generated in a weakly collisional magnetized plasma by a spatially nonuniform high-frequency whistler-mode field. The sources of the quasistationary magnetic field are nonlinear currents generated due to the longitudinal and transverse components of the ponderomotive force, acting on charged particles in the spatially localized high-frequency pump field. The dynamics of the excited magnetic fields has been analyzed. It was found that the settling time of the quasistationary magnetic field is determined by the switching-on time of the high-frequency field and the propagation of pulsed current and magnetic fields from the region of their generation occurs with the velocity of low-frequency whistler waves.     

Hydromagnetic Rayleigh problem with Hall effect

An exact solution of the governing equations of motion for the flow, induced by an impulsive start of a long flat plate, under the action of a strong transverse magnetic field with Hall currents, has been obtained in a closed form. Some interesting results along with the asymptotic cases of very small and very large times are discussed, accounting for the influence of the governing parameters on the flow character. It is seen that the time taken by the flow to attain the steady state increases due to Hall effect. The final steady flow is characterised by a boundary layer, of which the thickness increases due to Hall current.On leave fromRavenshaw College, Cuttack, Orissa, India.The author is indebted to Dr. R. S.Nanda for his help in the preparation of this paper, and to Dr. P.Mitschka for his constant ercouragement.     

Transit of beams of charged particles through a non-adiabatic magnetic field

The possibility of obtaining beams of particles with high transverse energies in a strong magnetic field is discussed. The motion of particles in a weakly non-adiabatic field is described by a linear non-homogeneous equation. The non-adiabaticity of motion is caused, in the first approximation, by the curvature of the magnetic lines of force. The conditions for a small spread of magnetic moments of the beam particles are established by solving the equation of motion. The transverse energy of particles and its spread can be varied by varying the shape of the magnetic field and the initial radial velocities of the particles. As a result of the conditions for a small spread of magnetic moments, a beam traversing a steep magnetic field gains a smaller magnetic moment than a beam passing through a field with a lesser slope.The author is indebted to Dr M. Seidl, DrSc, for valuable discussions on the subject, and to Dr M. Ondráek, CSc for help in the computer calculations.     

Hydromagnetic slip flow with heat transfer in an inclined channel

The problem of steady two-dimensional laminar flow in slip flow regime of a viscous incompressible and electrically conducting fluid through an inclined channel of rectangular cross-section in presence of a transverse magnetic field has been considered. The walls of the channel are assumed to have prescribed temperatures and finite conductivities. The expressions for the velocity component, induced magnetic field and the temperature are obtained and their numerical results are shown graphically.     

On hydromagnetic turbulent shear flow between moving parallel planes

Hydromagnetic turbulent shear flow of viscous, incompressible, electrically conducting fluid between two infinite uniformly porous moving parallel planes in the presence of axial and transverse magnetic field has been studied by the semi-empirical method. The expressions for the mean distributions for velocity and magnetic field for turbulent shear flow have been obtained for both the cases. As particular cases, the results have been obtained if the planes are fixed. The solutions obtained when the magnetic field is axial have been shown graphically for turbulent and laminar flows.     

ELECTRON DIFFUSION IN A NON-UNIFORM ELECTRIC FIELD AND A UNIFORM MAGNETIC FIELD

A Monte Carlo simulation technique has been used to model the electron transport beharlot, especially the electron diffusion motion, in the cathode fall region of a glow discharge under the influence of a non-uniform electric field and a transverse magnetic field perpen-dicular to the cathode sheath electric field. Three types of collisions (elastic, excitation and ionization) are taken into account in our model. The electron free flying time is determined by the electron-neutral atom collision frequency. We focus attention on the electron diffusion distance and velocity. The electron-neutral atom collision processes and the electron drift velocity are also studied. The results indicate that with the increase of the magnetic field the electron diffusion distance increases and the electron diffusion velocity decreases. The results Mso show that the collision processes are enhanced by the magnetic field, this is in agreement with the experimental result. However, the axial magnetic field does not affect the electron transport behavior.     

Anomalous plasma diffusion transverse to high magnetic fields in InSb

Investigations on the ambipolar diffusion of an electron-hole plasma transverse to a magnetic field have been carried out in InSb. A plasma layer, produced at the surface of the sample by a short laser pulse, was moved through the sample in crossed electric and magnetic fields by the Lorentz force. From the broadening of the plasma layer we found at 80K an enhanced diffusion coefficient which decreased proportional to 1/B for magnetic fields higher than 1T, constrary to the expected classical 1/B ² dependence. Furthermore, the diffusion coefficient was strongly dependent on the electric field. The ambipolar drift velocity, measured simultaneously showed a classical behaviour. Together with the enhanced diffusion we observed instabilites in the electric potential. The instability threshold decreased towards the cathode.     

MHD cylindrical shock wave in self-gravitating gas

Summary Similarity solutions of the propagation of cylindrical blast waves through a self-gravitating polytropic gas caused by an instantaneous release of finite energy are investigated theoretically including the influence of transverse magnetic field. A comparative study of the distributions of velocity, density, mass, pressure, temperature and magnetic field has been illustrated through figures. The authors of this paper have agreed to not receive the proofs for correction.     

Magnetogravitational Instability of a Thermally Conducting Rotating Plasma through a Porous Medium

Magnetogravitational instability of an infinite homogeneous, viscous, thermally conducting, rotating plasma flowing through a porous medium has been studied with the help of relevant linearized perturbation equations, using the method of normal mode analysis. Rotation is taken parallel and perpendicular to the magnetic field for both, the longitudinal and the transverse modes of propagation. The joint influence of the various parameters do not, essentially, change the Jeans' criterion but modifies the same. The adiabatic velocity of sound is being replaced by the isothermal one due to the thermal conductivity. Porosity reduces the effects of both, the magnetic field and the rotation, in the transverse mode of propagation, whereas the rotation is effective only along the magnetic field for an inviscid plasma. The viscosity removes the effect of rotation in the transverse mode of propagation.     

Influence of Finite Larmor Radius with Finite Electrical and Thermal Conductivities on the Gravitational Instability of a Magnetized Rotating Plasma Through a Porous Medium

An infinitely extending homogeneous, self-gravitating rotating magnetized plasma flowing through a porous medium has been considered under the influence of Finite Larmor Radius (FLR) and other transport phenomena. A general dispersion relation has been derived through the linearized perturbation equations. Longitudinal and transverse modes of propagation have been discussed for the rotation with axis parallel and perpendicular to the magnetic field. The joint influence, of the aforesaid parameters, does not essentially change the Jeans' criterion of instability but modifies the same. The adiabatic sonic speed has been replaced by the isothermal one due to the thermal conductivity. It is further observed that the FLR corrections have stabilizing effect for an inviscid, non-rotating plasma, in case of transverse propagation. Rotation decreases the Larmor radius, whereas the porosity reduces the effects of rotation, FLR, and the magnetic field. Viscosity removes the effects of both, the roation, and the FLR corrections.     

Effect of an axial magnetic field on the Poiseuille flow of a nematic liquid crystal

The effect of an axial magnetic field on the Poiseuille flow of nematicp-azoxyanisole (PAA) has been computed using the Ericksen-Leslie continuum theory. The apparent viscosity decreases appreciably in the presence of the magnetic field. Orientation and velocity profiles for different shear rates and magnetic fields are presented.     

Soliton generation via continuous stokes acoustic self-scattering of hypersonic waves in a paramagnetic crystal

A new mechanism is proposed for continuous frequency down-conversion of acoustic waves propagating in a paramagnetic crystal at a low temperature in an applied magnetic field. A transverse hypersonic pulse generating a carrier-free longitudinal strain pulse via nonlinear effects is scattered by the generated pulse. This leads to a Stokes shift in the transverse hypersonic wave proportional to its intensity, and both pulses continue to propagate in the form of a mode-locked soliton. As the transverse-pulse frequency is Stokes shifted, its spectrum becomes narrower. This process can be effectively implemented only if the linear group velocity of the transverse hypersonic pulse equals the phase velocity of the longitudinal strain wave. These velocities are renormalized by spin-phonon coupling and can be made equal by adjusting the magnitude of the applied magnetic field. The transverse structure of the soliton depends on the sign of the group velocity dispersion of the transverse component. When the dispersion is positive, planar solitons can develop whose transverse component has a topological defect of dark vortex type and longitudinal component has a hole. In the opposite case, the formation of two-component acoustic “bullets” or vortices localized in all directions is possible.     

Trapping of a supersonic beam in a traveling magnetic wave

Here we report on a new approach to the magnetic deceleration of supersonic beams, based on the generation of a propagating wave of magnetic field. Atoms and molecules possessing a magnetic dipole moment, in so-called low field seeking quantum states, are trapped around a node of the propagating wave. The wave travels at a desired velocity in the direction of the supersonic beam, which can be chosen to match a velocity class populated in the beam. An additional quadrupole guide provides transverse confinement, independently of the decelerator itself. Our technique has been conceived to generate a smooth motion of the magnetic wave, which should optimize the efficiency of the trapping during a future Zeeman deceleration of the beam. We demonstrate the trapping of metastable argon atoms in a magnetic wave traveling at selected, constant velocities.     

Transverse-longitudinal coherence function of a sound field for line-of-sight propagation in a turbulent atmosphere

Using the narrow-angle and Markov approximations, a formula for the transverse-longitudinal coherence function of a sound field propagating in a turbulent atmosphere with temperature and wind velocity fluctuations is derived. This function, which applies to observation points that are arbitrarily located in space, generalizes the transverse coherence function (coherence when the observation points are in a plane perpendicular to the sound propagation path), which has been studied extensively. The new result is expressed in terms of the transverse coherence function and the extinction coefficient of the mean sound field. The transverse-longitudinal coherence function of a plane sound wave is then calculated and studied in detail for the Gaussian and von Kármán spectra of temperature and wind velocity fluctuations. It is shown, for relatively small propagation distances, that the magnitude of the coherence function decreases in the longitudinal direction but remains almost constant in the transverse direction. On the other hand, for moderate and large propagation distances, the magnitude of the coherence decreases faster in the transverse direction than in the longitudinal. For some parameters of the problem, the coherence function has relatively large local maxima and minima as the transverse and longitudinal coordinates are varied. With small modifications, many results obtained in the paper can be applied to studies of electromagnetic wave propagation in a turbulent atmosphere.