Volume 95, Issue 6, 15 March 2004
Index of content:
- PLASMAS AND ELECTRICAL DISCHARGES (PACS 51-52)
Three regimes of growth of a Gaussian ripple on a uniform plane electromagnetic wave front in a plasma95(2004); http://dx.doi.org/10.1063/1.1645643View Description Hide Description
Starting with the scalar wave equation and relevant expressions for nonlinear dielectric constant of plasma, the propagation of a Gaussian ripple on a plane wave front of uniform intensity has been studied in the paraxial approximation. In the plane of the ripple width (along the y axis) and the ratio of the electric field intensities of the ripple and the main beam at (along the x axis) three distinct regions (for a given intensity of the main beam) can be identified which correspond to steady divergence, oscillatory divergence, and self-focusing of the ripple. The variation of the ripple width with distance of propagation has also been obtained for typical points in the three regions.
95(2004); http://dx.doi.org/10.1063/1.1645998View Description Hide Description
The motion of macroparticles (MPs) emitted from the cathode into the vacuum arc plasma jet is considered taking into account asymmetric ion bombardment of the MP surface. The MP velocity is increased up to 0.17 of the plasma jet velocity for an initial MP radius and up to 0.3 of the plasma jet velocity for The electric current density distribution within the MP caused by the asymmetric plasma bombardment was calculated assuming homogeneous internal conductivity. The electric potential difference between the apex and antiapex points is for an MP radius of while the average MP electric potential relative to the surrounding plasma is Interaction between the internal electric current and the magnetic field used to collimate the plasma jet rotates the MPs with a frequency of
95(2004); http://dx.doi.org/10.1063/1.1647269View Description Hide Description
An investigation on the soft x rays emitted in a 2.2 kJ Mather-type dense plasma focusdevice using a multichannel diode spectrometer and a simple pinhole camera is reported. Emitted x rays associated with different shapes (hollow, solid, and hemispherical) of anode and in hydrogen/nitrogen gas medium are compared. The structure of x-ray emitting sites as well as x-ray yields were found to be strongly influenced by the shape of the anode and the filling gas pressure. The maximum yield of 2.2 J into 4π sr was obtained in the case of hemispherical anode in hydrogen gas medium. The x-ray pinhole images of the collapsed plasma with the hemispherical anode indicated spot-like structure having 500–800 μm in diameter. On the contrary, other anode shapes showed columnar pinched structure of 8–10 mm in length and 1–2 mm in diameter. Results indicated that an appropriate design of the anode could enhance the x-ray yield by more than tenfold in a conventional low energy dense plasma focusdevice.
Analytical fit of the probe characteristic for finite ion temperature values: Justification of the radial model applicability95(2004); http://dx.doi.org/10.1063/1.1650540View Description Hide Description
This article deals with an extension of the radial model for the sheath that surrounds a cylindrical or spherical Langmuir probe immersed in a plasma in which positive ion thermal motion is taken into account. The dependence of the electric potential profile and of the characteristic on the positive ion temperature is obtained. Moreover, a different parameterization is established from a numerical fit of the characteristic as a function of the probe radius, the biasing potential, and the ratio between the positive ion temperature and the electron temperature. This parameterization allows us to obtain an analytical approximation to the potential profile and the sheath edge. Finally, it also gives us a means of justifying under what conditions the radial model can be applied in plasmas with finite positive ion temperature.