Overdense microwave plasma heating in the CNT stellarator
Abstract
Overdense plasmas have been attained with 2.45 GHz microwave heating in the low-field, low-aspect-ratio CNT stellarator. Densities higher than four times the ordinary (O) mode cutoff density were measured with 8 kW of power injected in the O-mode and, alternatively, with 6.5 kW in the extraordinary (X) mode. The temperature profiles peak at the plasma edge. This was ascribed to collisional damping of the X-mode at the upper hybrid resonant layer. The X-mode reaches that location by tunneling, mode-conversions or after polarization-scrambling reflections off the wall and in-vessel coils, regardless of the initial launch being in O- or X-mode. This interpretation was confirmed by full-wave numerical simulations. Also, as the CNT plasma is not completely ionized at these low microwave power levels, electron density was shown to increase with power. A dependence on magnetic field strength was also observed (for O-mode launch) and discussed.
Cite
@article{arxiv.1708.02684,
title = {Overdense microwave plasma heating in the CNT stellarator},
author = {K. C. Hammond and R. R. Diaz-Pacheco and A. Koehn and F. A. Volpe and Y. Wei},
journal= {arXiv preprint arXiv:1708.02684},
year = {2018}
}
Comments
24 pages, 12 figures