Simulation of a scintillator-based fast ion loss detector for steady-state operation in Wendelstein 7-X (invited)

Abstract

A quantitative theoretical framework has been created to model neutral beam injection and fast ion losses in the Wendelstein 7-X (W7-X) stellarator, including a novel method to develop synthetic diagnostics for fast ion loss detectors (FILDs) of many types, such as scintillating and Faraday Cup FILDs. This is the first time that this has been done in stellarator geometry with this level of fidelity, providing a way for fast ion losses to be predicted more precisely in future stellarator experiments and in W7-X. Simulations of the signal seen by a Faraday Cup FILD have been completed for multiple W7-X plasmas and show close agreement with the measured signals. This method is now applied to an actively water-cooled, scintillator-based FILD, which is currently in development to measure the fast ion loss distribution in W7-X in greater detail. The design makes use of a double slit to measure energy-and-pitch-angle-resolved losses of both co-going and counter-going fast ions. The diagnostic, which can be inserted to different radial positions, has been designed to withstand steady-state heat fluxes of up to 120 kW/m2 along with additional transient heat loads of 100 kW/m2 lasting for up to 20 s at a time. Simulations of W7-X standard magnetic configuration show up to 8 × 1013 (s−1 cm−2) ion fluxes onto the sensor from each neutral beam source and no signal from the counter-going slit. These simulations will help inform experimental proposals for future W7-X campaigns after installation of this diagnostic.

Validation of a synthetic fast ion loss detector model for Wendelstein 7-X

“…Possible future areas of exploration include measuring the energy flux to the exterior of the NIFS-FILD and comparing this to simulation, or detailed metrology of the NIFS-FILD head for comparison to the CAD model. This model has recently been expanded for use in simulating an additional FILD on W7-X, the S-FILD, and used to predict the total flux of fast ions to this diagnostic's scintillator plate as well as the spatial distribution of this flux [35]. A possible future step would be to apply this model to the FC-FILD as well.…”

“…In addition, a third scintillating-type FILD, the S-FILD, is currently in development by Princeton Plasma Physics Laboratory, the University of Seville, and the Max Planck Institute for Plasma Physics [33][34][35]. A complete design has been produced, and the S-FILD is expected to be constructed and implemented on W7-X for an upcoming experimental campaign.…”