Synthetic fast ion loss detectors for Wendelstein 7-X

A quantitative method has been developed for modelling fast ion loss detectors (FILDs) on the Wendelstein 7-X (W7-X) stellarator, producing the first simulated FILD signals which quantitatively agree with experimental measurements on W7-X. This method, which aims to compensate for the difficulty in simulating FILD signals due to the scale difference between the plasma and the FILD entrance apertures, makes use of gyro-orbit expansions and virtual detection planes to simulate fast ion fluxes to FILD sensors from a computationally tractable number of simulated fast ions.

This method is first applied to the Faraday Cup FILD provided by the National Institute for Fusion Science in Japan (NIFS-FILD), which has been used during two experimental campaigns on W7-X. Actual W7-X experimental conditions are simulated and close agreement is found between predicted signals and those measured by the NIFS-FILD, providing a validation of the method.

Next, the method is applied to a scintillating FILD (S-FILD) in development by Princeton Plasma Physics Laboratory, the University of Seville, and the Max Planck Institute for Plasma Physics, in order to predict total ion flux to the S-FILD as well as the spatial distribution of this flux which will be measured by a fast video camera. These predictions can inform experimental proposals for future W7-X campaigns after this diagnostic is installed, as well as suggesting a potential change to the aperture design to allow the S-FILD to better measure counter-going fast ions.