Mainz 2022 – scientific programme
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P: Fachverband Plasmaphysik
P 19: Poster II
P 19.26: Poster
Thursday, March 31, 2022, 16:00–17:30, P
Simulations of the O-X mode conversion in MAST-U — •Alf Köhn-Seemann1, Bengt E. Eliasson2, Simon J. Freethy3, Lucy A. Holland4, Roddy G.L. Vann4, and David Woodward2 — 1IGVP, University of Stuttgart, Germany — 2SUP, Department of Physics, University of Strathclyde, Glasgow, U.K. — 3Culham Centre for Fusion Energy, Culham, U.K. — 4York Plasma Institute, York, U.K.
Coupling microwaves to plasmas where the density exceeds the cut-off density can be achieved by electron Bernstein waves (EBWs). These are electrostatic waves that have no high-density cut-off and are very well absorbed at the electron cyclotron resonance and its harmonics. In addition, EBWs can drive very efficiently toroidal net currents, which is of particular importance in spherical tokamaks like MAST-U.
EBWs can be excited via a two step mode conversion process: an injected O-mode couples to an X-mode at the O-mode cut-off which then propagates outwards again and can couple to EBWs in the vicinity of the upper-hybrid resonance. The overall efficiency is strongly dominated by the O-X conversion. In this work, we present simulations of the O-X coupling process in the MAST-U geometry. Different codes have been used and benchmarked against each other. The dependence on plasma scenarios, beam geometry and plasma density fluctuations were investigated in detail. High conversion efficiencies on the order of 90 % were found making this an attractive heating scheme for MAST-U.