Description
SPARC, a medium-sized high-field tokamak, is under assembly and preparation for its first campaign, which aims to demonstrate net fusion energy. Operation at both the full 12.2 T field and a reduced ~8.5-8.9 T field is considered. The operational points are governed by the resonance conditions required for delivering power to plasma from the only auxiliary heating system in SPARC, Ion Cyclotron Range of Frequencies (ICRF) heating, which operates at 120±1 MHz. The corresponding heating schemes are ³He minority (plus harmonic T) for the ~12 T scenario and H minority (plus harmonic D and T) for the ~8 T scenario. 20 MW of ICRF power will be installed for the first campaign, with 10 antennas delivering power to the plasma. Both L- and H-mode plasmas are planned on the path to achieving Q>1. For H-mode operation, the ICRF heating must meet the requirements of the L-H transition power threshold, sustain the H-mode, deliver power robustly in the presence of ELMs, and steer the plasma into the Q>1 operational space.
In this contribution, we present an analysis of ICRF power coupling – through impedance match tuning and edge density tailoring – as well as core power absorption via parameter scans of resonance location, minority species concentration, antenna wave spectrum, and core plasma profiles. The effects of ICRF fast ions on heating efficiency, fusion gain enhancement, and sawtooth stabilisation are studied to obtain a self-consistent picture of ICRF interaction with the plasma. In the all-metal-wall device, tungsten sputtering and accumulation are concerns which might limit the operational range for both ICRF power level and plasma profiles. Prediction and minimisation of sputtering associated with ICRF physics processes are carried out using RF sheath modelling, near-field optimisation and extrapolation of sputtering rates from ASDEX Upgrade experimental data to SPARC.