A simple model for the instrument function of scintillator-based fast-ion loss detectors (FILD) has been developed which accounts for the orbit trajectories in the 3D detector geometry and for the scintillator response. It allows us to produce synthetic FILD signals for a direct comparison between experiments and simulations. The model uses a weight function formalism to relate the velocity-space distribution of fast-ion losses reaching the detector pinhole to the scintillator pattern obtained experimentally, which can be understood as a distortion of the velocity-space distribution due to the finite resolution of the system. The tool allows us to recover the undistorted velocity-space distribution of the absolute flux of fast-ion losses reaching the detector pinhole from an experimental measurement using tomographic inversion methods, which can reveal additional details of the velocity-space distribution of the lost ions.

A conceptual design of a reciprocating fast-ion loss detector for ITER has been developed and is presented here. Fast-ion orbit simulations in a 3D magnetic equilibrium and up-to-date first wall have been carried out to revise the measurement requirements for the lost alpha monitor in ITER. In agreement with recent observations, the simulations presented here suggest that a pitch-angle resolution of ∼5° might be necessary to identify the loss mechanisms. Synthetic measurements including realistic lost alpha-particle as well as neutron and gamma fluxes predict scintillator signal-to-noise levels measurable with standard light acquisition systems with the detector aperture at ∼11 cm outside of the diagnostic first wall. At measurement position, heat load on detector head is comparable to that in present devices.