Boron powder injection in WEST during long pulses with a fully actively cooled, ITER grade tungsten divertor

The installation of a fully actively cooled ITER grade tungsten (W) divertor on WEST enables 1000 s pulses. Usage of W plasma facing components (PFCs) introduces high-Z impurities into the plasma, which can cause significant radiative losses. To prevent this, W PFCs are often coated with protective layers of low-Z material. Active wall conditioning using an impurity powder dropper (IPD) is being studied on WEST. Recently, boron (B) powder was dropped during a series of 20 s long pulses with m_B^total ~855 mg, more than double than previously achieved. The maximum drop rate achieved without disruption was 58 mg/s, far greater than in 2021. This discrepancy may be due to the new divertor: new actively cooled W monoblocks vs. used inertial W-coated CFC. Another important difference is the response of P_rad to injected B, showing a rollover during B injection. Spectroscopy measurements suggest O gettering to be the cause. To interpret the experimental results, a modelling workflow with SOLEDGE-EIRENE fluid boundary code and Dust Injection Simulator code was employed to study the transport of B in the plasma and its effects on PFCs, e.g. reduced recycling of D and low-Z impurities, decreasing divertor plasma density and increasing confined energy W_MHD.