Proposal for Solid Boron Injection in ITER for Real-Time Wall Conditioning

The ITER Organization (IO) is proposing to change to full tungsten plasma facing components. As risk mitigation to achieve and sustain Q=10, the IO has proposed real-time solid boron injection (SBI) during plasma operation to supplement gaseous discharge boronization (GDB). Boron getters oxygen and reduces tungsten sputtering. In areas with significant plasma wall interactions, boron coatings are expected to be short-lived at high plasma performance. The system should be used sparingly, as boron redeposition retains tritium, which must be minimized in ITER to comply with nuclear safety. SBI can limit and precisely control the amount of boron injected. Some design requirements and concepts for SBI in ITER will be presented based on results with pellet injection or granule dropper systems installed at or by PPPL on machines around the world. Boron from 5 µm – 2 mm diameter was injected at calibrated rates of 2 – 200 mg/s during plasma operation on AUG, DIII-D, EAST, KSTAR, LHD, TFTR, WEST, and W7-X, to improve wall conditions and plasma performance. The boron is ionized in the plasma edge and then deposited on plasma-wetted surfaces. Reduced tungsten sputtering was observed following discharges with SBI on AUG, EAST, and WEST. Experimental SBI results will be compared with modelling of erosion and redeposition of boron to attempt to quantify the amount of boron needed and if one SBI location is sufficient in ITER. SBI control requirements and operation scenarios for ITER will also be described.