Operation Modes of Hot-Cathode Plasma Source for Linear Devices

Abstract

Operation of a plasma source with a hot disk cathode and a cylindrical hollow anode in axial magnetic field is sensitive to the cathode-to-anode diameter ratio. When the cathode edge maps along magnetic field lines to the inner anode surface, the discharge voltage is relatively low, and the plasma stream with moderate density occupies the entire cross-section of the anode bore. By contrast, when the cathode projection is fully inside the anode bore with the radial cathode-to-anode gap ∼ 1 cm, the discharge voltage jumps to much higher values exceeding 250 V. The plasma density profile becomes Gaussian-like with the width matching the cathode radius according to magnetic flux surfaces. The plasma density in the high-voltage cross-field discharge reaches 10 13 cm −3 , and the discharge parameters almost do not change with magnetic field up to 1.5 kG in the anode area. This plasma source is suitable for the use in linear devices for plasma-material interaction studies.

Conceptual design of the ALIANCE-T mirror experiment

“…After exiting the magnetic mirrors, the plasma flare expands and hits the plasma receiving electrodes ('endplates'). Besides the obvious benefit of continuous operation, there are several advantages to using an RF generator instead of a hotcathode [12] or arc-discharge plasma source in ALIANCE-T. One of them is the symmetry of both plasma and gas flows in the machine, which greatly simplifies the analysis of experimental data. Another advantage is that such generators have demonstrated [13] high-efficiency gas ionization (<10% nonionized gas leak at 10 kW), which limits the residual gas pressure in the vessel and reduces charge-exchange losses to an acceptable level (see section 5), even with a basic pumping system.…”