Initial Boron Powder Injection Experiments on WEST*

Boron powder (< 150 mm) was injected at various drop rates into lower single null (LSN) L-mode discharges in WEST, using a recently installed impurity powder dropper (IPD) developed at PPPL. IPDs provide real-time wall conditioning of plasma-facing components without the use of diborane gas. The long-pulse capabilities of WEST and the full-W environment make it an excellent testbed for evaluating the viability of the IPD at reactor relevant timescales. The discharges presented featured  I_p ~ 0.5 MA, t_pulse = 12-30 s, n_e,0 ~ 4x10¹⁹ m^-3, and P_LHCD ~ 4.5 MW. During powder injection, a clear reduction in SOL D I and low-Z intrinsic impurity line intensities was observed, suggesting a reduction in recycling and possible screening of low-Z impurities. Concurrently, the plasma stored energy increased up to 25% depending upon the powder drop rate. The largest increases in stored energy were achieved at the highest drop rates (9-17 mg/s), possibly due to the large reduction in divertor recycling. Initial analysis suggests these increases in stored energy may be the result of stabilized ion temperature gradient (ITG) modes due to fuel dilution similar to gaseous impurity seeding experiments.