P.V. Minashin1, R.R. Khayrutdinov1,2, A.B. Kukushkin1,3, V.E. Lukash1 Effect of Multi-Pass Absorption of Electron Cyclotron Heating Wave on Initial Stage of Discharge in ITER-like Tokamak P.V. Minashin1, R.R. Khayrutdinov1,2, A.B. Kukushkin1,3, V.E. Lukash1 1Tokamak Physics Institute, NRC Kurchatov Institute, Moscow, Russia 2Troitsk Institute for Innovation & Fusion Research, Troitsk, Russia 3Nuclear Research National University MEPhI, Moscow, Russia TH-P3-32 A model is suggested for calculating the efficiency of absorption of external EC power, γECH, in tokamaks at initial stage of discharge. Single-pass absorption of injected EC radiation is evaluated with scaling obtained using the OGRAY code. For subsequent multi-pass absorption, after first reflection of EC wave from the wall of vacuum chamber, we develop a model assuming isotropy/uniformity of respective EC radiation intensity in plasma. The model modifies the approach of CYNEQ code developed for plasma-produced EC radiation transport at moderate and high EC harmonics in fusion reactor plasmas. Results are given for ITER initial stage of discharge for the case: (a) multiple reflection of injected EC wave (O-mode) from the wall; (b) polarization scrambling in wall reflections. Fig. 1. Boundary conditions for intensity of the EC radiation, I, for the case of mode-dependent reflection and polarization scrambling Rςςʹ – wall reflection with ς to ςʹ mode conversion, ‘inc’ (incoming), ‘ref’ (reflected) and ‘out’ (outgoing) Te, eV ne, 10(19) m(-3) Multi Single Single-pass O-wave absorption scaling, obtained with OGRAY code, vs. multi-pass absorption model ROO = 0.6, ROX = 0.05