On the criteria guiding the design of the upper electron-cyclotron launcher for ITER

Abstract

Abstract. Electron cyclotron waves injected from an antenna located in the upper part of the vessel will be employed in ITER to control MHD instabilities, particularly neoclassical tearing modes (NTMs). The derivation of the NTM stabilization criteria used up to now to guide the optimization of the launcher is reviewed in this paper and their range of validity elucidated. Possible effects leading to a deterioration of the predicted performance through a broadening of the EC deposition profile are discussed. The most detrimental effect will likely be the scattering of the EC beams from density fluctuations, resulting in a beam broadening in the 100% range. The combined impact of these effects with that of beam misalignment (with respect to the targeted surface) is discussed for a time slice of the standard Q = 10 H-mode scenario.

On the stabilisation of locked tearing modes in ITER and other large tokamaks

“…Similarly, theoretical calculations of island stabilisation for ITER have focused on stabilising the island during the rotating phase (e.g. [9,10]). This strategy has emerged from a concern about the damaging impact of locked islands on plasma performance, and in particular from a concern about the impact on disruptivity.…”

“…The equations have been modified by incorporating coefficients and other parameters such that the predictions of the equations provide an approximate fit to the available experimental data. Nearly all of the calculations of ECCD NTM stabilisation for ITER have made use of subsets of these equations [9,23,25,35,36].…”

“…for an EC-driven current density profile that is Gaussian with radial width w dep . We do not consider the impact of radial misalignment of the EC wave with the resonant surface, a previously identified challenge for NTM stabilisation [9,10,23,35,49,50], as it becomes much less severe for the large deposition widths of interest in this study. The CD efficiency η CD = I CD /P RF and unbroadened deposition width are obtained from [25].…”

“…Most previous studies of NTM stabilisation for ITER have also made use of the generalised Rutherford equation [9,23,25,35,36], albeit in a simplified form. More importantly, only one previous study [35] considered the implications of island deceleration and mode locking on rotating island stabilisation, studying in that case the permitted time delay between mode seeding and EC stabilisation.…”

Feedback-controlled NTM stabilization on ASDEX Upgrade

“…Such localised currents can so far only be driven using ECCD. For ITER the request on the ECCD width may be fulfilled only marginally especially when taking into account a potential broadening of the beam due to density fluctuations [2]. Under these circumstances the amount of current driven outside the island must be minimised by modulation of the beam with respect to the O-point of the rotating island.…”