New boronization system at ASDEX Upgrade

Abstract

The coating of plasma facing components (PFC) with boron significantly improves the performance of plasma operation in magnetic fusion devices. The boron layer traps residual oxygen in the vacuum vessel, thus reducing radiative losses due to collisions between the plasma and this impurity. Furthermore, it reduces the erosion of high-Z material from the plasma facing components due to plasma wall interaction. This prevents accumulation of high-Z impurities in the plasma during discharges. The coating is achieved by deposition during a glow discharge using diborane (B2D6). A new system for injecting diborane into the vessel, pumping and treatment of residual process gas was installed at ASDEX Upgrade. This new system allows semi-automatic boronization cycles with adjustable process times and pressures, resulting in different boron layer thicknesses. A feedback loop between mass flow controllers in the gas supply and a pressure gauge at the vacuum vessel keeps the process pressure constant at the optimal value to create a homogeneous boron layer. The system meets industrial safety standards for the treatment of the toxic diborane gas.