Real-time wall conditioning in lower and upper divertor configurations at DIII-D

Real-time injection of low recycling powders in cumulative amounts of >100 mg has improved wall conditions and reduced carbon and oxygen influxes at DIII-D in upper, lower, single, and double null configurations. Pure boron and boron nitride powders have been injected in L-mode and H-mode plasmas at several tens of mg/s for durations up to 3 s into the plasma crown or the divertor. Post-mortem analysis of witness samples confirmed the growth of B layers at rates of 1 nm/s, sufficient to re-instate conditions similar to glow-discharge boronization. Real-time powder injection has also been successfully applied at AUG, EAST, KSTAR, NSTX, WEST, LHD, and W7-X for wall conditioning, reduction of C and W sputtering and enhanced plasma performance. Modeling shows that 1-10 µm particles ablate fully in the scrape-off layer (SOL) while >100 µm particles may introduce additional impurity sources in the core. Far SOL ion flows mostly determine boron deposition patterns on the plasma-facing components. The results suggest real-time surface conditioning can extend the operational window for long-pulse and low-collisionality scenarios and help replenish eroded walls in next-step devices.