The Auburn Linear EXperiment for Instability Studies (ALEXIS).
The Auburn Linear Experiment for Instability Studies has 5 main components–-the antenna (A), a standard 6-way cross (B), the main chamber (C), a custom box that can be used for optical access (D), and a double-walled water-cooled section with a tee attached (E). The ports are numbered 1 (closest to the antenna) to 7 (farthest from the antenna). The electromagnet coils are lettered (a) through (i).
The filament source in the back of the chamber (Section e) is shown here. Each filament is made from 3.5 in. long and 0.01 in. diameter tungsten.
The filament assembly includes (a) the tungsten filament, (b) the aluminum ring used to hold the assembly in place in the water-cooled section, (c) a stainless steel mesh that is used to bias the filament plasma, (d) an aluminum disk to ensure the RF plasma remains grounded, and (e) a Macor disk to electrically isolate the RF plasma from the biasing mesh.
A schematic of the hot filament source circuit. PS-1 controls the bias on the mesh and the blocking disk, PS-2 controls the bias voltage on the filament source relative to the biasing mesh, and PS-3 resistively heats the filament source.
The blocking disk used to block out the center of the RF plasma and to terminate the filament plasma. One side of the disk is biased to the same potential as the stainless steel mesh so that the entire filament plasma is maintained at a single potential independently of the RF plasma.
An example of a double probe used in ALEXIS.
Initial plasma potential (left) and electric field (right) measurements in ALEXIS. As the grid bias is decreased, the plasma potential decreases and the radial electric field becomes smaller. The radial electric field is localized across the boundary of the filament and RF plasmas.
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