Interaction of boron and nitrogen-rich plasmas with tungsten wall*

There is an interest in the conditioning of tungsten divertor by controlled injection of boron and boron nitride powder during the plasma discharges [1]. However, it remains unclear how plasma consisting of boron, nitrogen and deuterium species interact with the tungsten wall. In this work, we study plasma material interaction using optical emission spectroscopy (OES) and high speed imaging for boron-rich ablating targets immersed in the nitrogen and nitrogen-hydrogen plasmas generated by two different methods: 1) the arc discharge between the tungsten electrodes [2] and 2) laser vaporization. In particular, our arc experiments revealed that boron ablation generates charged boron droplets. OES measurements demonstrated a strong effect of addition of the hydrogen to the nitrogen atmosphere on observed boron, nitrogen and tungsten species. For laser vaporization, we also detected molecular species including BN, B2N, N2. These results appear to be consistent with our thermodynamic simulations. [1] A. Borotolon et al., PSI Conference, Princeton, NJ, USA, June 2018; [2] Y. W. Yeh et al., Sci. Rep.-UK 7 (2017).