Isotropic Plasma Column Research Articles

Wall stabilization of the rigid ballooning m = 1 mode in a long-thin mirror trap

The prospect of stabilization of the m = 1 ‘rigid’ ballooning mode in an open axially symmetric long-thin trap with the help of a conducting lateral wall surrounding a column of isotropic plasma is studied. It was found that for effective wall stabilization, the beta parameter β must exceed some critical value β crit. The dependence of β crit on the mirror ratio, radial pressure profile, axial profile of the vacuum magnetic field, and the width of vacuum gap between plasma and lateral wall was studied. Minimal critical beta at the level of 70% is achieved at zero vacuum gap, although stability zone at β → 1 exists even at extremely wide vacuum gap. It is shown that when a conducting lateral wall is combined with conducting end plates simulating attachment of the end MHD stabilizers to the central cell of an open trap, there are two critical beta values and two stability zones that can merge, making stable the entire range of allowable beta values 0 < β < 1.

Microwave radiation of cylindrical plasma column

The travelling wave antennas representing a column of isotropic plasma and a plasma column placed into external infinitely large magnetic field have been theoretically and numerically investigated and compared. The relationships of radiation patterns as a function of the plasma density, geometrical parameters of the plasma cylinder and the radiation wavelength were also investigated. We considered both the linear antennas and the radiating antennas with wavelengths close to the antenna radius. An axially symmetric E-wave was studied. The need of taking into account the radial distribution of antenna current was shown. The dependence of normalized radiation patterns on the wave-slowing was analyzed. The characteristic value of plasma density was found; if this value is exceeded, the normalized radiation patterns are sharp directional and have the main lobe located at small angle towards the antenna axis. For the magnetized plasma this characteristic value of density is much smaller than for the isotropic one. With the rise of the plasma density the level of side lobes gets smaller.

An experimental study of the axial structure of a gas discharge sustained by a surface electromagnetic wave in the presence of a uniform external magnetic field

Examines experimentally the axial profiles of the plasma parameters (electron temperature Te and the electron number density n) of a helium low-pressure gas discharge column sustained by a travelling electromagnetic wave in the presence of a strong magnetic field for two values of magnetic induction corresponding to the magnitudes of omega c/ omega =2.5 and 5 respectively ( omega c is the electron cyclotron frequency and omega is the wave angular frequency). It is found that the electron temperature is diminished and the plasma density is increased (accompanied by a decrease of its axial gradient) in comparison with the magnitudes of the same parameters and characteristics of an isotropic plasma column. The measured axial plasma density gradients are compared with theoretically calculated ones and the agreement between theory and experiment is good.

Narrow-beam antennas using cylindrical columns of isotropic plasma†

It has been reported earlier (Gupta 1970) that a radiation pattern with single or multiple narrow beams may be obtained when a column of isotropic plasma is excited by a ring source of electromagnetic waves placed inside the column. This investigation has been extended to the case where the waves on plasma column are excited by a waveguide source. Also the TE- and TM-modes of propagation for both the excitation schemes have been discussed. Narrow beams of radiation may be obtained in all these four eases. It is observed that the small beamwidths (1° to 5°) are obtained for high plasma densities (∊p = 01) and large plasma column radii (k 0b≥15.0)

Propagation in isotropic plasma waveguides

The paper considers the propagation behaviour of a circular waveguide enclosing either an axial or an annular column of isotropic plasma. The effect of the glass walls of the container required to enclose an actual gaseous plasma is exactly taken into account. The phase-change and attenuation coefficients of both structures are computed for a range of parameters relevant in microwave applications. It is evident that the circularly symmetric mode of the axial column has characteristics suited to devices employing forward waves, whereas the circularly symmetric mode of the annular structure is suited to devices employing the backward wave. A brief review of possible passive- and active-device applications of the structures is presented and some of the limitations on the realisation of these devices noted. An equivalent transverse-network representation for a radially stratified isotropic structure is presented in the Appendix, thereby making possible the computations described in the paper.

Plane-wave scattering by a magnetoplasma cylinder

The scattering of H-polarised plane waves by an infinitely long axially magnetised cylinder of uniform plasma is investigated for the case in which the radius of the cylinder is small in comparison with the wavelength of the incident wave. The scattering amplitude is found to be a maximum at two frequencies, which are shown to be related to the familiar dipolar resonant frequency of an isotropic plasma column. Approximate expressions for the two resonant frequencies are derived.

Radiation from an electric dipole in a plasma column

The radiation characteristics of an axially oriented electric dipole in an isotropic plasma column are investigated. Surface waves are found to be excited for frequencies of less than 1/√2 times the plasma frequency. The dependence of the power carried by the surface wave, as well as that carried by the space wave, on the frequency and the radius of the plasma column is examined. The surface waves are found to be excited with maximum efficiency at about half the plasma frequency. The radiation pattern in the far zone is evaluated and found to have, in general, a maximum in the broadside and a null in the end-fire directions. The normalised radiation resistance is found to vary as the square of the frequency for small column dimensions and high frequencies.