Measurements of the Energy Distribution of Ions Lost From the Scrape-Off Layer of C-2W

We report on measurements of the ion energy distribution function (IEDF) of ions lost from the scrape-off layer (SOL) of the C-2W experiment [1] at TAE technologies. C-2W consists of a field reversed configuration (FRC) core plasma surrounded by a mirror-confined SOL on open field lines. The open field lines extend past a mirror at either end of the central vessel and then expand by a factor of B_max/B_min~30 into large divertor vessels where they terminate on sets of concentric circular electrode plates. The expanding magnetic field in the divertors is designed to impede cold electrons generated at the edge of the machine from flowing back into the central vessel. This should allow an ambipolar potential to develop inside the mirror-confined region of the SOL and reduce electron heat transport out of the region. We used electrostatic ion energy analyzers mounted on the divertor electrode plates [2] to measure a drifting-Maxwellian shaped IEDF. The results show that an ambipolar potential develops in the central vessel and give insight into electron heat transport on the SOL.

[1] M. Binderbauer, et. al. AIP Conference Proceedings 1721, 030003 (2016)

[2] M. E. Griswold et. al., to be published in Rev. Sci. Instrum.