Radial Profiles Of Plasma Potential Research Articles

Characterization of DC glow discharge plasma in co-axial electrode geometry system by nonlinear dynamical analysis tools

This paper reports plasma behavior in an un-magnetized, co-axial electrode geometry DC glow discharge plasma system. Fluctuations and hysteresis in discharge characteristics have been observed when the electrode system has a central anode configuration. The important fact is that fluctuations and hysteresis in discharge characteristics are not observed in a central cathode configuration. The radial profile of plasma potential shows that it is less than the anode potential, so current continuity is maintained in this current-driven system. This paper also attempts to identify the source of order-to-chaos-to-order in floating potential oscillations with respect to the discharge characteristics. When discharge current (Id) increases after the first negative differential resistance region, the system self-organizes and stabilizes into a state of periodic oscillations. Chaotic behavior is a possible development of new dynamical states in the discharge, which develops from an initial high frequency, low amplitude oscillations (in the range 11.6 mA < Id < 15 mA) and, thereafter, transits to low frequency, large amplitude oscillations at Id >15 mA. In the reverse path of discharge characteristics, the oscillations are more regular than in the forward path. Before the production of low frequency, large amplitude oscillations, the current oscillations follow a similar pattern to the floating potential oscillations. As it transits from chaotic to low frequency, large amplitude floating potential oscillations, discharge current oscillations show a chaotic type of behavior.

Propagation of the end-face electrodes potential in the plasma volume of rf discharge

The problems of the creating a stationary electric field in a magnetized plasma of rf discharge are investigated. Helmholtz coils create a magnetic field in a cylindrical vacuum chamber with a diameter of 85.6 cm and a length of 220 cm. Radio-frequency discharge is generated at a frequency of about 5 MHz. Radio-frequency power absorbed by the plasma is in the range of 0.5–1.5 kW. Negatively charged electrodes are placed on the end-face of the chamber. We study three cathode configurations with diameters from 55 to 295 mm. Argon is used as the working gas. Radial profiles of plasma potential, electron density and electron temperature are obtained. The dependence of plasma potential in the discharge center on the voltage of end-face electrodes is studied.

Experimental Investigation of Non-Isolated Dust Particles on the Plasma Characteristics in Direct Current System

This paper reviews the radial profile of plasma parameters in the present and absent of nonisolated dust particles at different positions from the cathode surface. The results of voltage and current discharge shown that the present of dust did not effect of the behavior of discharge voltage but it decreased the discharge current. However, the measurement of radial distribution of plasma parameters along the cathode at different distance (2 cm and 4 cm) from it shown that, all plasma parameters are non-homogenous distribution along the cathode in the cathode sheath and plasma bulk. Moreover, according to radial profile of plasma potential, the charge of copper dust particles is negative in the plasma sheath but it is charged postively in the plasma bulk.

Applicability of Heavy Ion Beam Probing for Stellarator W7-X

A feasibility study for the heavy ion beam probe on the Wendelstein 7-X (W7-X) stellarator was done to provide measurements of the radial profiles of plasma potential, density, and their fluctuations. Calculations of probing Tl+ beam trajectories were done for the various W7-X magnetic configurations with Btor = 2.5 T. They show that satisfactory access is possible for K11-N11 port combination. The trajectory optimization aiming for the maximal plasma observation was done for the chosen port combination.

Plasma properties downstream of a low-power Hall thruster

Triple Langmuir probes and emissive probes were used to measure the electron number density, electron temperature, and plasma potential downstream of a low-power Hall thruster. The results show a polytropic relation between electron temperature and electron number density throughout the sampled region. Over a large fraction of the plume, the plasma potential obeys the predictions of ambipolar expansion. Near the thruster centerline, however, observations show larger gradients of plasma potential than can be accounted for by this means. Radial profiles of plasma potential in the very-near-field plume are shown to contain large gradients that correspond in location to the boundaries of a visually intense plasma region.

Laser-induced-fluorescence characterization of velocity shear in a magnetized plasma column produced by a segmented, Q-machine source

Control over the radial profile of one component of ion drift speed U, either perpendicular or parallel to the magnetic field, is demonstrated in the magnetized plasma column for two configurations of a double-ended Q machine in which one of the hot plates is segmented into a central disk and two concentric annuli. Each hot plate can be heated to ∼1800°C, and the segmented hot plate is bombarded with barium vapor, resulting in quasineutral, magnetized, barium-ion plasma. Since the electric potential in the plasma magnetically maps to the segments, the radial profile of plasma potential, and hence the E×B flow, can be made inhomogeneous. This configuration is referred to as the perpendicular configuration. A negatively biased, cross-sectional mesh, inserted between the two ends of the plasma column, reflects electrons from each source causing the radial profile of potential on the nonsegmented source side of the mesh to become uniform. In traversing the mesh sheath from the segmented source side, where the radial potential profile is inhomogeneous, to the nonsegmented source side, where the radial potential profile is homogeneous, the ions experience an axial acceleration that has an inhomogeneous radial profile. This configuration with the mesh is referred to as the parallel configuration. Laser-induced-fluorescence is used to measure the ion-velocity-distribution function on the nonsegmented-source side with and without the mesh inserted. Measurements show that the above configurations result in ion temperature anisotropy, 1<(T⊥∕T‖)<5, and radially nonuniform ion flows with a maximum in the shear profile (dU⊥∕dx)max as large as 0.6Ωi and (dU‖∕dx)max as large as 0.17Ωi where Ωi is the ion gyrofrequency.

Radial profile of plasma potential with various biased electrode ring configurations in a toroidal plasma

An experimental study on behavior of radial profile of the floating potential with different biased electrode ring configurations has been carried out in a currentless magnetized toroidal plasma. Radial profile of the floating potential has been measured by biasing single ring of various sizes and two rings. It is observed that floating potential profile of a well shaped with controllable depth, hill-cum-well shaped, and almost flat positive potential can be obtained. Results on parameter dependence studies of floating potential on the bias voltage, magnetic field, and gas pressure are presented.

Control of radial potential profile and nonambipolar ion transport in an electron cyclotron resonance mirror plasma.

A radial profile of plasma potential is successfully controlled by the use of circular concentric segmented electrodes at both ends in a simple axisymmetric electron cyclotron resonance mirror plasma. An enhancement of radial nonambipolar ion transport is clearly observed under a condition where the ion Larmor motion is strongly modified by a radial electric field directed outward.