Overview of first NBI fast ion results from W7-X*

We present an overview of  first fast ion experiments in the optimized stellarator Wendelstein 7-X (W7-X). The improved fast-ion behaviour is essential for applicability of stellarators as a fusion reactor and is one of the optimization criteria for the W7-X field geometry.

The neutral beam injection (NBI) system of the Wendelstein 7-X (W7-X) stellarator is commissioned during the 2018 experimental campaign. The NBI system consists of two boxes with two sources each. The four sources inject 55 keV hydrogen with approximately 1.7MW power, each. The injection geometry is quite radial and the two boxes produce stellarator-antisymmetric initial fast ion populations in phase space.

The confined fast ion population is measured with fast ion hydrogen alpha spectroscopy (FIDA) and ion cyclotron emissions probes (ICE) as well as via the excited MHD activity using magnetic pick-up coils. The lost fast ions are measured with a fast ion loss diagnostics probe (FILD) as well as monitored with infrared and visible light cameras viewing the plasma facing components.