Analysis of boron powder injection experiments on WEST with interpretive modelling suite*

Boron (B) powder injection with an impurity powder dropper (IPD) is being studied on a number of tokamaks as an alternative to glow discharge boronization, including WEST, due to the possibility of real-time conditioning, which makes it relevant for the machines with longer uptime. In the B powder injection experiments in 2023 different effects of the injection were witnessed in WEST, among them signs of the reduction of light impurity ion fluxes at the lower divertor and a roll-over of W concentration in the confined plasma past the injection rate of ~20 mg/s. Presence of B coating layers' formation was also supported by a cumulative effect of B injection on average radiances of B-II and W-I lines at the PFCs, including at the midplane limiters at the high and low field sides. To analyse the effect of B injection on WEST plasma and PFCs an interpreting modelling suite using SOLEDGE-EIRENE (boundary plasma modelling) and Dust Injection Simulator (tracking injected B particles) was employed to replicate measurements from one of the pulses, and the effect of B injection on low-Z impurity recycling was estimated. Using the resulting simulation as a basis for further modelling studies, scans of input power, midplane electron density and radial position of the IPD were performed to estimate an effect of these parameters on B transport, showing low sensitivity of B influx wall profile to the plasma temperature and density, but high sensitivity to the position of the IPD relative to the poloidal flux stagnation point.