Authors: F. M. Poli, E.D. Fredrickson, N. Bertelli

Abstract:

Time-dependent simulations are used to evolve self-consistently plasma discharges in combination with a modified Rutherford equation for calculation of Neoclassical Tearing Mode (NTM) stability in response to Electron Cyclotron (EC) feedback control in ITER. The main application of this integrated approach is to support the development of control algorithms by analyzing the plasma response with physics-based models and to assess how uncertainties in the detection of the magnetic island and in the EC alignment affect the ability of the ITER EC system to fulfill its purpose. Simulations indicate that it is critical to detect the island as soon as possible, before its size exceeds the EC deposition width, and that maintaining alignment with the rational surface within half of the EC deposition width is needed for stabilization and suppression of the modes, especially in the case of modes with helicity (2, 1). A broadening of the deposition profile, for example due to wave scattering by turbulence fluctuations, can even be favorable in the case of the (2, 1 )-NTM, by relaxing the over-focussing of the EC beam and improving the stabilization at the mode onset. Pre-emptive control reduces the power needed for suppression and stabilization in the ITER baseline discharge to a maximum of 5 MW, which should be reserved and available to the Upper Launcher during the entire flattop phase. With pre-emptive control ITER would be still able to demonstrate a fusion gain a.hove Q = 9.

Submitted to: Nuclear Fusion
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Download PPPL-5353 3.8 MB (31 pp)
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