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arXiv · 1708.02684

Overdense microwave plasma heating in the CNT stellarator

K. C. Hammond·R. R. Diaz-Pacheco·A. Koehn·F. A. Volpe·Y. Wei
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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.

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K. C. Hammond, R. R. Diaz-Pacheco, A. Koehn, F. A. Volpe, Y. Wei. 2017-08-09. Overdense microwave plasma heating in the CNT stellarator. https://doi.org/10.1088/1361-6587/aa9a7c

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