Fusion Science and Technology / Volume 53 / Number 1 / January 2008 / Pages 220-236
Technical Paper / Special Issue on Electron Cyclotron Wave Physics, Technology, and Applications - Part 2
The remote steering (RS) system (C. P. Moeller, Proc. 23rd Int. Conf. Infrared and Millimeter Waves, September 7-11, 1998, University of Essex, pp. 116-118) provides a method of steering a millimeter-wave beam for electron cyclotron heating (ECH) and current drive (CD) applications without having moveable mirrors close to the plasma. The input beam is coupled into a square corrugated waveguide having a length such that the phase and amplitude profile of the input beam is repeated at the waveguide output. In the most basic implementation, by injecting the input beam at an angle relative to the waveguide axis, the output beam is radiated at that same angle. The steering range (typically to ±12 deg) and the focusing ability are strongly limited because of the restricted space for the launcher in a fusion device, which results in a large deposition profile in the plasma. However, the waveguide and optical arrangement can be modified to either increase the steering range and/or focus the RS system. For example, if a converging beam is injected into the waveguide, the output beam's waist will be projected far from the waveguide aperture. Likewise, a tapered square waveguide can be used to increase the scanning range of the RS system beyond that of ±12 deg. This paper will investigate such hybrid designs of the RS launcher, providing alternative configurations for optimizing the launching configuration, depending on the requirements of a given ECH and CD system.