Measurement of End Losses from C-2W's Open Field line Plasma

In TAE Technologies’ current experimental device, C-2W (also called “Norman”) [1], the FRC core plasma is surrounded by a mirror-confined scrape-off layer on open field lines. These open field lines expand by a factor of ~30 in the divertors before terminating on a set of concentric electrodes that are used for plasma biasing. An array of energy analyzers and bolometers mounted on the divertor electrodes [2] measures axial power losses as well as the electron temperature and ion energy distribution function (IEDF) of the plasma at the termination point of the open field lines. We use this system to study the sheath and pre-sheath voltage drops that form in the expanding magnetic field divertors at various levels of electrode bias. We show that a "clean divertor" ambipolar potential of (~4.5 Te) forms to limit electron parallel transport whether or not the biasing system is active.

[1] H. Gota et al., Nucl. Fusion 59, 112009 (2019)

[2] M. Griswold et. al. "Upgraded Diagnostic Array for End Losses from C-2W's Open Field Line Plasma" Poster Presented at the 63rd Annual Meeting of the APS-DPP (November, 2021)