High performance plasma source development to simulate iter divertor conditions

Summary form only given. To study plasma-surface interactions (PSI) in conditions similar to those expected in the divertor of ITER and other future fusion devices, the FOM Institute for Plasma Physics Rijnhuizen is building a linear plasma generator called Magnum-PSI. In this machine, targets will be exposed to steady-state particle and energy fluxes similar to those predicted at the ITER strike points in a comparable background pressure and magnetic field: 1024 ions m"2 s"1 and 10 MW m"2 at ~1 Pa and 3 T. The width of the plasma beam will be up to ~10 cm. In this contribution we report on the development of the plasma source for this experiment. Magnum-PSI will use a cascaded arc plasma source. This is a flowing, direct-current, wall-stabilized, thermal arc discharge. Based on data from experiments performed on the development device Pilot-PSI, we have formulated an empirical model for the scaling of the hydrogen plasma production by a cascaded arc as a function of the input power, the gas flow rate and the discharge channel diameter. This model describes the dominant physical processes inside the discharge channel. Our investigations furthermore showed the importance for the plasma production of processes in the nozzle/anode region. With an optimized anode geometry and an applied magnetic field, the discharge current is forced to extend into the plasma beam (well outside the plasma source). The extra power deposition into the plasma beam leads to a greatly enhanced ion flux towards the target (~0.5 m downstream). Experiments with sources with multiple closely packed discharge channels have been performed and showed that depending on conditions and when operating on argon, three separate beams can be made to mix into a single wide beam.