Progress On The Iter Upper Launcher Millimeter Wave Design And Testing

The main purpose of the ITER ECH upper launcher is to control magnetohydrodynamic activity, in particular neoclassical tearing modes, in the plasma. The mm-wave optical system is optimized to insure that the eight RF beams are all focused to a small beam width at the resonance location. The current design uses two miter bends per beam and a focusing mirror for each group of four beams to orientate the beams into onto a single steering mirror for each group of four beams. The toroidal and poloidal launch angles have been determined by numerical calculations to ensure nearly coincident deposition over the entire steering range. The system is being tested with a low RP power beam to ensure that the optical system directs and properly focuses each beam. The fourth mirror is steered using a frictionless and backlash-free mechanical system which is pneumatically actuated using helium to provide rapid and accurate angular positioning of the mirror. A first prototype of the steering mechanism has been constructed to demonstrate the manufacturability, the actuation principle and to develop an adequate control strategy to meet ITER requirements.