High-impedance wire grid method to study spatiotemporal behavior of hot electron clump generated in a plasma.

High-impedance Wire Grid (HIWG) detector has been developed to study spatiotemporal behavior of a hot electron clump generated in an electron cyclotron resonance (ECR) plasma. By measuring the floating potentials of the wire electrodes, and generating structure matrix made of geometrical means of the floating potentials, the HIWG detector reconstructs the spatial distribution of high-temperature electron clump at an arbitrary instant of time. Time slices of the spike event in floating potential revealed the growth and decay process of a hot spot occurs in an ECR plasma.

Experimental studies on ion acceleration and stream line detachment in a diverging magnetic field.

The flow structure of ions in a diverging magnetic field has been experimentally studied in an electron cyclotron resonance plasma. The flow velocity field of ions has been measured with directional Langmuir probes calibrated with the laser induced fluorescence spectroscopy. For low ion-temperature plasmas, it is concluded that the ion acceleration due to the axial electric field is important compared with that of gas dynamic effect. It has also been found that the detachment of ion stream line from the magnetic field line takes place when the parameter |f(ci)L(B)∕V(i)| becomes order unity, where f(ci), L(B), and V(i) are the ion cyclotron frequency, the characteristic scale length of magnetic field inhomogeneity, and the ion flow velocity, respectively. In the detachment region, a radial electric field is generated in the plasma and the ions move straight with the E×B rotation driven by the radial electric field.

Interchange mode in the presence of dust.

The linear and nonlinear development of an electrostatic interchange mode which involves a magnetized nonuniform electron-ion fluid in the presence of nonuniform static charged dust grains is investigated. The charge on grains is taken as spatially dependent, and the consequences of that condition are investigated. It is shown that standardly accepted stabilization of the interchange mode in the presence of negatively charged grains can be violated due to the spatial dependence of the charge on grains. Also, the ion drift, which is caused by the action of a gravity term perpendicular to the magnetic field lines, is taken as nonuniform as a result of the magnetic field nonuniformity, and it is shown that due to such a nonuniformity the instability condition can be significantly modified. In the nonlinear regime several types of coherent stationary vortex structures are found: namely, dipolar and tripolar vortices and vortex chains. The dipolar vortex is found to propagate in the direction of the ion drift, while the tripole and vortex chains are carried by the drift flow. The spatial dependence of these structures is determined by parameters describing the nonuniformity of the equilibrium plasma.

Analytical description of a neutral-induced tripole vortex in a plasma.

An analytical description of a stationary triple vortex, observed in a cylindrical plasma, is presented. The concentration of neutrals, which is rather high in the experiment, turns out to be of crucial importance due to a spatially dependent distribution. In the radial direction the neutral concentration is paraboliclike, yielding an effective radial force directed towards the axis of the system. This neutral force causes the rotation of the plasma in the direction which is opposite to the E-->xB--> drift. The stationary triple vortex develops for a starting Gaussian-density distribution and a rigid-body rotation of the plasma column.

Electrostatic interaction in dusty plasma.

Two modifications of the standard description of electrostatic interaction in a dusty plasma are emphasized. First, the Coulomb-type potential profile is not applicable at very short distances around a dust grain, due to the polarization of the charge on the grain, i.e., the image charge effect, and, second, at larger distances, the standard Debye-Hückel potential screening is modified due to nonlinear corrections in the expanded Boltzmann distribution for plasma particles.