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(EX/P5-15) Third Harmonic X-mode Elelctron Cyclotron Resonance Heating on TCV using Top and Low Field Side Launch

L. Porte¹⁾, S. Alberti¹⁾, G. Arnoux¹⁾, Y. Martin¹⁾, J.P. Hogge¹⁾, T.P. Goodman¹⁾, M.A. Henderson¹⁾, E. Nelson-Melby¹⁾, A. Pochelon¹⁾, M.Q. Tran^1)
 
1) CRPP - EPFL, Lausanne, Switzerland

Abstract.  A third harmonic X-mode ECRH system, X3, comprising 3 0.5 MW, 118 GHz gyrotrons, has been brought into operation on TCV. For these first experiments 1.0 MW is launched from the top and the rest is launched from the low field side. Both launchers can be steered poloidally and toroidally. In the final configuration the full 1.5 MW will be launched from the top. X3 has been used to heat TCV plasmas at density exceeding cut off for second harmonic ECRH (X2) ( n_cutoff = 0.4 ^. 10²⁰m^{- 3}). Experiments show that the TORAY ray tracing code makes predictions of the absolute X3 power absorption and the optimal plasma launcher geometry that are verified by diamagnetic loop measurements at density exceeding X2 cut off. TORAY can be used as a tool in optimising X3 heating of TCV H-modes. Using a data base built up during previous experiments, a class of ohmic H-mode has been identified that maximises a figure of merit for X3 absorption; n_eT_eK (K - elongation; n_e&T_e are line averages). This allows one to predict suitable discharges for X3 heating in H-mode. Results of experiments conducted to verify these predictions and to explore ways of broadening the TCV H-mode operating space will be presented.

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