B 2-Eirene study of the effects of heating in a linear plasma device

Introduction On the ITER divertor targets, extreme particle and energy fluxes of around 1024 m−2s−1 and 10 MWm−2 are expected. Therefore, relevant plasma surface interaction (PSI) studies in experiments, capable of controlled production of these extreme plasma conditions, are important. The linear plasma generator Pilot-PSI [1] is a pilot experiment to be succeeded by the larger device Magnum-PSI [2]. It consists of a cascaded arc that generates a magnetized hydrogen plasma with an axial magnetic field strength of up to 1.6 T over a distance of 55 cm. In contrast with tokamak experiments, the linear geometry makes it very accessible for diagnostics and in-situ surface analysis. The capability of realizing the ITER divertor conditions, extreme fluxes at low electron and ion temperatures of < 5 eV, with a beam diameter of around 2 cm makes Pilot-PSI unique. The B2-Eirene code SOLPS4.2 [3], which is also used to model the ITER SOL and divertor plasma, has been adapted to simulate Pilot-PSI and Magnum-PSI, continuing the work presented in [2]. The two-dimensional multi-species fluid code B2 [4] describes the plasma. It is self-consistently coupled to the three-dimensional Monte Carlo neutral transport solver Eirene [5]. Figure 1 shows the cylindrically symmetric grid used for simulating Pilot-PSI. An auxiliary heating is usually used in linear plasma generators to prevent the plasma beam from cooling down to the ambient gas temperature before reaching the target. Two heating scenarios are investigated in this paper: RF heating and ohmic heating. In Magnum-PSI, RF heating will be applied in the vicinity of plasma inlet. Closer to the target the beam will lose a considerable amount of its power, for instance due to molecule assisted recombination. In contrast to RF heating, ohmic heating (passing an electric current along the beam) can effectively heat the plasma over the whole length of the beam.