Profile Control/Heating and Current Drive Issues

1. Profile Control/Heating and Current Drive Issues Presented byT. C. Luce (H & CD for R. Prater) General Atomics Presented at FESAC sub-committee meeting San Diego, CA June 25, 2007

2. Profile Control Issues for DEMO • Operation of DEMO in advanced scenarios will require model-based control for access to and maintenance of the desired operating scenario • Current and rotation profile control are the only clear DEMO-relevant methods known at present • Model-based control is needed because: • Resistive times in DEMO are too long for simple PID control • Actuators will be relatively weak (by definition) at high fusion gain and are typically uni-directional • Authorization of a fast-track DEMO will require a well-characterized, robust operating scenario

3. Bridging the Gap to DEMO • Three elements are required for profile control • Control domain map • Includes landscape and boundaries • Can be first-principles, empirical, or mixed • Control method • Beyond the state of the art at present • DEMO-compatible current and rotation profile diagnostics • Development of both can be carried out to a large extent the present generation of tokamaks, but only with a substantial increase in dedicated resources (people, experimental time, hardware) • Next generation superconducting machines allow validation and optimization • ITER is the only device to add the essential missing ingredient--self-heating • A dedicated DEMO-similar low-fluence companion tokamak may be needed for software testing and personnel training

4. Heating and current drive physics issues for DEMO • Physics models of ICRF, LHCD, NBI, and ECH/ECCD need to be tested under reactor conditions -- first-principles models are in development and validation -- careful experiments can extrapolate to reactor conditions -- support of SciDAC, SWIM, and FSP are critical to generating the ability to understand and predict H&CD inputs and their effects on the plasma • ARIES AT DEMO calls for FWCD/ICRF and LHCD, but ECCD may be useful for off-axis CD and for NTM control and NBI for off-axis CD and introducing momentum for rotation • ECCD has the best-developed physics and technology of these H&CD methods, and the extrapolation to DEMO from ITER is small • NBI needs resolution of off-axis CD physics and FP interactions -- NB technology for ITER satisfactory for DEMO -- 120 keV beams for edge rotation should be tested

5. LHCD and ICRF have major technology issues regarding the antennas • LHCD and ICRF have evanescent barriers between the antenna and the plasma, but in a DEMO the antenna may not be placed near the plasma • For LHCD there are some potential solutions which should be aggressively tested: -- injection of gas near the antenna (JET, JT-60U) -- PAM launcher (Tore Supra, FTU; revalidation on C-Mod, EAST, and KSTAR should follow) • For ICRF new antenna concepts appear to be required, but no plan is in place -- e.g., ITER design calls for unrealistically high voltage -- possible alternates: segmented straps or combline should be developed on present tokamaks