The ITER ECH FS Launcher design for an optimized Physics Performance

The purpose of the ITER electron cyclotron resonance heating (ECRH) upper port launcher is to stabilize the neoclassical tearing mode (NTM) by driving currents (co-ECCD) locally inside either the q=3/2 or 2 island1. A narrow current deposition profile along with a wide steering range is required to deposit current inside all islands forming at relevant flux surfaces over the wide spectra of possible ITER plasma equilibria. The ITER launcher reference design uses a front steering (FS) mirror that provides optimum focusing for NTM stabilisation and the possibility for a wide steering range. A two-mirror system (focusing and steering) decouples the steering and focusing functions of the launcher for enhanced performance2 over that of a remote steering concept. The steering mechanism uses a frictionless system3, flexure pivots replace traditional bearings and a gas pneumatic actuator replaces mechanical feeds. Two FS launcher designs are under consideration: an NTM launcher providing access over the region in which the NTMs are expected to occur (0.64<=rho (subscript psi)<=0.93), and an Extended Physics (EP) launcher increasing the access range (0.40<=rho (sobscript psi)<=0.94) seeking a synergy with the equatorial launcher for an enhanced ECH system for ITER4. In either design, the launcher is capable of injecting up to 16MW per port (eight beams of up to 2.0MW). The best allocation of the four ports with respect to engineering and physics aspects is discussed.