Taming Tungsten in Tokamaks: Electron-Ion recombination of tungsten ions with complex atomic structure

ABSTRACT: Tungsten is the material of choice for the divertor of the international ITER tokamak because of its favorable thermo-mechanical properties. The radiation losses that are associated with the presence of tungsten ions in the plasma limit the plasma operation and performance. In order to understand the behaviour of these impurities in the plasma, detailed knowledge of the atomic collision processes of tungsten ions in the plasma is required. The most relevant processes are electron-impact ionization and electron-ion recombination. Rate coefficients for electron-ion recombination of moderately charged tungsten ions were measured at the Heidelberg heavy-ion storage ring TSR [1,2]. It was found that they are up to orders of magnitude larger than the ones from the ADAS database which is widely used for the modeling of fusion plasmas. Novel concepts in atomic collision theory had to be applied in order to (partly) reconcile experiment and theory [2-4]. [1] S. Schippers et al., PRA 83 (2011) 012711 [2] K. Spruck et al., PRA 90 (2014) 032715 [3] N. R. Badnell et al., PRA 85 (2012) 052716 [4] V. A. Dzuba et al., PRA 88 (2013) 062713