Experimental validation of Fast Ion Loss Detector modeling on Wendelstein 7-X

We present the first validated synthetic diagnostic model for fast ion loss detectors (FILDs) in Wendelstein 7-X (W7-X), which include the Faraday cup FILD (FC-FILD), the FILD provided by the National Institute for Fusion Science (NIFS-FILD), and the scintillating FILD (S-FILD) currently in development.

Fast ion confinement is an optimization target of W7-X. The heating systems of W7-X include neutral beam injection (NBI), which produces 55 keV hydrogen ions. Information about the success of this optimization can be gleaned by measuring the confinement of these fast ions with FILDs, which often measure not only fast ion loads but also their energy and pitch angle. Accurate simulation of the expected signals is necessary to design FILDs that are sensitive to the expected fast ion distributions in W7-X as well as to compare measured losses to predicted confinement.

Using the Monte Carlo codes BEAMS3D and ASCOT5, NBI ions are followed from injection to a virtual plane near the FILD. Simultaneously, simulations in ASCOT5 are used to determine a probability matrix, binned by location, normalized momentum, pitch angle, and gyrophase, for transmission from the plane, through the FILD aperture, and onto the sensor. This probability matrix is convoluted with the simulated ions reaching the plane, allowing the FILD signal to be simulated from a computationally tractable number of simulated ions. Simulated signals will be presented covering a range of W7-X experimental conditions and compared to experimental data.