An alternative ECRH front steering launcher for the ITER upper port

Presently, a remote steering (RS) antenna [C.P. Moeller, A method of remotely steering a microwave beam launched from a highly overmoded corrugated waveguide, in: Proceedings of the 23rd International Conference on IRMMW, Colchester, UK, 1998] is envisioned for launching the electron cyclotron current drive (ECCD) from the ITER upper port. The RS launcher has a strong engineering advantage in that the steering mechanism is placed outside of the ITER blanket, however, at the cost of reduced performance. In particular, the launcher has a limited steering range and a wide deposition width that results in sub-marginal performance for neoclassical tearing mode (NTM) stabilization. An alternative front steering (FS) launcher is proposed [M.A. Henderson, R. Chavan, F. Sanchez, Front Steering ECCD Launcher Study for the ITER upper port, CRPP LRP 791/04], which has a wider steering range and a narrower deposition width offering above marginal performance for all plasma equilibria investigated. A two-mirror system (one focusing and one flat steerable) is used to project the RF beam waist far into the plasma. The steering mechanism avoids frictional surfaces that risk to block during operation and uses a gaseous He pneumatic system as a control actuator.