ICRF Heating for SPARC*

ICRF is the proposed auxiliary heating method (30 MW at 120 MHz) for the SPARC experiment based on its successful use on Alcator C-Mod and elsewhere. ICRF heating for SPARC will have the fortunate combination: modest antenna loading for good power coupling and high single-pass-absorption for effective heating. The antenna loading, mainly set by the density profile near the plasma edge, is similar to that on Alcator C-Mod and much higher than that on ITER. The single-pass-absorption of the fast waves, strongly affected by the machine size, is close to that on ITER and higher than that on Alcator C-Mod. Additionally, the k_|| spectrum of the launched RF waves is a critical element influencing both coupling and absorption; the antenna will be optimized to launch k_|| spectra for good performance. To minimize the impact of impurities at high RF power, the latest techniques in antenna design and operation, such as field alignment of the antenna and image current minimization, will be considered in the analysis and design. To cope with ELMs and other load-varying events, ferrite tuners will be used in transmission lines for real-time matching. The latest result from analysis and modeling will be presented.