Progress on the ITER upper launcher millimeter-wave design and testing
The aim of the ITER electron cyclotron heating and current drive upper launcher (UL) is to control magnetohydrodynamic activity in the plasma, in particular neoclassical tearing modes, requiring a narrow and peaked deposition of the radio-frequency (rf) power. The millimeter-wave (mm-wave) system of the UL is optimized to ensure that the eight rf beams are all focused to a small beam width at the resonance location. The present design uses two mitre bends per beam and a focusing mirror for each set of four beams, orientating each set onto a single steering mirror (SM) to inject it into the plasma. The SM is rotated using a frictionless and backlash free pneumo-mechanical system. A first prototype of the SM has been constructed to demonstrate the manufacturability and the actuation principle and to develop an adequate control strategy. A test program has been developed to ensure the integrity of the launcher from the pre-build-to-print design phase (research and development) up to the tests after maintenance. This paper presents a general overview of the system, a description of the progress in the mm-wave optical layout, low-power tests, alignment specifications of the mm-wave components, and SM capabilities to meet the ITER requirements.