Integrated campaign to study the stationary inertial Alfvén wave in the laboratory and space regimes

Abstract

A small, off-axis mesh-anode electrode at one plasma-column end is used to create a paraxial channel of electron current and depleted density in the large plasma device upgrade at UCLA. We show that the on-axis, larger, surroundingplasma column rotates about its cylindrical axis because a radial electric field is imposed by a multiple-segmented-disc termination electrode on the same end as the mesh-anode electrode. The radial profile of azimuthal velocity is shown to be consistent with predictions of rigid-body rotation. Launched inertial Alfvén waves are shown to concentrate in the off-axis channel of electron current and depleted plasma density. In the absence of launched waves, time varying boundary conditions, or spatially structured boundary conditions, a non-fluctuating, non-traveling pattern in the plasma density is shown to arise spontaneously in the channel, but only in the combined presence of electron current, density depletion, and spontaneously in the channel, crossfield convection (i.e. rotation). These results may be relevant to the stationary Alfvén wave in the inertial regime in space and laboratory plasmas.

ExB flows for high-throughput plasma mass separation

“…On the other hand, positive biasing up to 20 V leads to a roughly uniform increase of the plasma potential for radii smaller than the largest electrode radius 99 . Similarly, imposing a radial voltage drop of up to 150 V across a single set of ring electrodes in an afterglow discharge of the Large Plasma Device has been showed to lead to a progressive increase of the potential in the core region 100 . These different results for positive biases are qualitatively consistent with results at low density discussed earlier.…”

“…This can in turn be used to affect the positive radial electric field near the radius of this ring. However, with the exception of the work by Tsushima and co-workers 92,93 and, to a lesser extent, by Koepke et al 100 , the ability to combine multiple rings to tailor the electric field profile throughout the plasma column has not yet been demonstrated. In addition, the contrasting results obtained with negative biases by Gilmore et al 99 on the one hand and Mase et al 89 on the other hand brings into question the practicality of forming a negative electric field (radial potential well) such as the one needed in the POMS-E concept (see Sec.…”

Laboratory evidence for stationary inertial Alfvén waves

“…The LAPD [3] is a linear-geometry, high-pulse-repetition plasma device that produces low-density, low-plasma-beta, helium or argon plasma. Plasma production occurs via ionization of a neutral gas by a 72 cm-diameter electron beam generated by a cathode-anode discharge at one end of the 18 m plasma column.…”

“…According to the theoretical model [7,11], StIA wave structures should only exist in the presence of both the parallel current and plasma rotation. When the MDE is unbiased, the space potential is uniform across the diameter of the plasma, whereas when a voltage bias is applied to the MDE, the shape of the space potential is peaked at the radial interface between the innermost and outermost groups of ganged plates [3]. The MDE is capable of producing controllable plasma drift across (8) , and what remains are fluctuations in the plasma density having wavefronts aligned with the direction of the rotational flow (clockwise), and collocated in the region of the ME (border outlined with a circle).…”

“…An Alfvén wave can be studied in detail in a long plasma column at a few facilities around the world. We report results obtained in the large plasma device (LAPD-U) [2] during the multi-year Space Plasma Campaign [3] at UCLA's Basic Plasma Science Facility. The objective of the work reported here is to find a new mechanism for structure and flows in plasma that could be responsible for accelerated, energetic particles from enhanced Alfvénic coupling and transport of mass, momentum, and energy.…”