Static Plasma Research Articles

VLF/ELF radiation patterns of arbitrarily oriented electric and magnetic dipoles in a cold lossless multicomponent magnetoplasma

With the use of a power integral formulation, a study is made of the vlf/elf radiation patterns of arbitrarily oriented electric and magnetic dipoles in a cold lossless multicomponent magnetoplasma. Expressions for the ray patterns are initially developed that apply for arbitrary values of driving frequency, static magnetic-field strength, plasma density, and composition. These expressions are subsequently specialized to vlf/elf radiation in a plasma modeled on the magnetosphere. A series of representative pattern plots are presented for frequencies between the proton and electron gyrofrequencies. These patterns illustrate the fact that focusing effects that arise from the geometrical properties of the refractive index surface tend to dominate the radiation distribution over the entire range from the electron gyrofrequency to 4.6 times the proton gyrofrequency. It is concluded that focusing effects should be of significant importance in the design of a vlf/elf satellite transmitting system in the magnetosphere.

Electrostatic-Probe Studies in a Flame Plasma

Simple theoretical considerations have yielded an approximate formula for the ion current per unit length Ii to a cylindrical probe (radius rp, bias voltage V) immersed in a collision-dominated moving plasma (subsonic velocity=vf, electron density=ne, ion mobility=μi). Ii=2(πμiε0)1/3(neevfV)2/3[log(Ii/2neevfrp)]2/3 (mks)where e is the electronic charge. This relation has been checked with a propane/air flame and a moving probe; it is found to be correct within ±50% over several decades of probe voltage, probe-flame velocity and flame ionization. A more favorable choice of μi in the above expression improves the agreement between theory and experiment to ±30%. Measurements of sheath thickness obtained from the mutual interference of two adjacent probes support the basic tenets of the theoretical model. It is concluded that, in many instances of probe measurements in flames and other collision-dominated plasmas, the velocity-dependent approach adopted in this paper will be necessary since very large errors can arise if the usual static continuum plasma formulas are used. (Errors of up to a factor of 100 have been reported.)

Slipping stream instability in anisotropic plasma with magnetic shear

Starting with the Chew, Goldberger & Low equations, an analysis is made of instability arising due to a tangential velocity discontinuity in a dilute plasma. The velocities on either side are parallel but oppositely directed. Two cases are considered: (i) the magnetic field is uniform and everywhere transverse to the motion, and (ii) the magnetic field vectors on either side are orthogonal, being parallel to the motion on one side and perpendicular on the other. The conditions for instability are obtained and it is found that the effect of magnetic field is destabilizing in both cases. The effect of orthogonality of magnetic fields on the conventional fire-hose instability for a uniform, static plasma is also discussed as special case.

Plasma confinement in ring-current configurations

The field from one or several ring-shaped coils can be used as a magnetic bottle for plasma confinement. In stationary operation as a fusion device the coils have to be suspended. A possible method is provided by magnetically screened leads. Earlier investigations by the author on this problem are extended by the following results: In the confinement volume defined by field lines encircling one or several ring-shaped coils a static plasma equilibrium should be possible even in the presence of the magnetic field from the leads. The particle losses introduced by the leads are mainly non-adiabatic. They are partly due to deviations from the constancy of the equivalent magnetic moment in some very small regions where the field is weak, partly to deviations from the constancy of the longitudinal invariant which arise when a particle passes the lead region repeatedly and in finite steps. These effects produce a scattering which displaces a particle randomly across the magnetic field by about one Larmor radius for each complete lead passage. It is equivalent to a kind of ambipolar diffusion across the magnetic field.

Two-Particle Correlation in a Static Plasma

The two-particle correlation theory for a static plasma is developed by an inverse application of Poisson equation theory, a less cumbersome and restrictive method than the usual Fourier theory. The theory is developed in computable form for nonfrigid two-component plasmas, and completely for warm plasmas. In the latter case it is found that the two-particle correlation function has only a small effect, and that only in the sheath.

Interaction of a Streaming Plasma with the Magnetic Field of a Two-Dimensional Dipole

The flow of an infinitely conducting plasma past a two-dimensional magnetic dipole oriented parallel to the flow has been considered by Hurley, among others. The problem consists of finding a vacuum magnetic field such that along a bounding field line whose location is to be found, the magnetic pressure balances the Newtonian dynamic pressure appropriate to the local slope of the boundary. A related problem has been solved by Cole and Huth; in their case there is no flow, but an isotropic static plasma surrounding the magnetic field region which exerts a constant pressure on the boundary. In the actual flow problem we would expect there to be a stagnant (trapped) region near the front. The stagnant flow would be at nearly constant pressure. Away from this region the Newtonian pressure would again be applicable. This problem, which is a mixture of those cited above, has been solved by an approximate technique due to Cockcroft. The solution is shown to have features of both the cited problems, as appropriate.

ELECTROMAGNETIC WAVES IN A BOUNDED, ANISOTROPIC PLASMA

The interaction of a plane, electromagnetic wave with a flat, uniform free-space – plasma interface in a static magnetic field has been considered for arbitrary angles of incidence. The dispersion relation for the plasma is a complex quartic equation which reduces to a quadratic if the static magnetic field and plasma boundary are oriented along any one of the rectangular co-ordinate axes. (These axes need not simultaneously be the same for the plasma and the magnetic field.)Numerical results are presented for the attenuation and phase constants for each of the two possible waves in the plasma, for each orientation of the static magnetic field. Data are given for various angles of incidence, plasma properties, and orientations of the static magnetic field relative to the plasma boundary.Inspection of the fields in the plasma reveals some interesting aspects. In certain cases, waves which appear to move upward towards the plasma interface exist. Since these waves may carry energy into the plasma, they have been referred to as "backward" waves. Totally reflected waves which have both finite attenuation and finite phase coefficients can also exist in the plasma. These have been termed "modified Sommerfeld" waves.

ELECTRIC IMPEDANCE OF ARBACIA EGGS

The alternating current resistance and capacity of suspensions of unfertilized and fertilized eggs of Arbacia punctulata have been measured at frequencies from 10(3) to 1.64 x 10(7) cycles per second. The unfertilized egg has a static plasma membrane capacity of 0.73 microf./cm.(2) which is practically independent of frequency. The fertilized egg has a static membrane capacity of 3.1 microf./cm.(2) at low frequencies which decreases to a value of 0.55 microf./cm.(2) at high frequencies. The decrease follows closely the relaxation dispersion of the dielectric constant if the dissipation of such a system is ignored. It is considered more probable that the effect is due to a fertilization membrane of 3.1 microf./cm.(2) capacity lifted 1.5 micro. from the plasma membrane, the interspace having the conductivity of sea water. The suspensions show a frequency-dependent capacity at low frequencies which may be attributable to surface conductance. The equivalent low frequency internal specific resistance of both the unfertilized and fertilized egg is about 186 ohm cm. or about 6 times that of sea water, while the high frequency data extrapolate to a value of about 4 times sea water. There is evidence at the highest frequencies that the current is penetrating the nucleus and other materials in the cytoplasm. If this effect were entirely due to the nucleus it would lead to a very approximate value of 0.1 microf./cm.(2) for the capacity of the nuclear membrane. The measurements do not indicate any change in this effect on fertilization.