Development of orbit weight functions for INPA and FILD fast ion diagnostics

A detailed characterization of the fast-ion (FI) distribution is fundamental for the success of future fusion machines such as ITER, as FI are a key source of energy and momentum. However, FI diagnostics usually probe small volumes of the phase space or integrate over larger portions of it, challenging any direct comparison with numerical results for model validation. Tomographic inversions arise as the best player to overcome these intrinsic limitations, as they allow us to eliminate the bias introduced by the diagnostics and to access the FI distribution function [1]. Combining information of different fast-ion diagnostics is key to achieve more precise and detailed reconstructions [2]. The natural framework to combine weight functions of different diagnostics are the so-called orbit coordinates a set of three variables (energy, maximum radial position and pitch at that radial position) that allows to fully identify the trajectory of a fast ion. These coordinates were used for inversion of Fast-Ion D- measurements [3], achieving the first ever 3D phase-space distribution of FI. We present the new module included in the FIDASIM [4] and FILDSIM [5] codes to calculate weight functions for the Imaging Neutral Particle Analyzer and Fast-Ion Loss Detector in orbit coordinates. We show how they scale with plasma profiles such as density, temperature or q₉₅, preparing the ground for future combined tomographic inversions and the selection of the best plasma scenario for that purpose.

[1] M. Salewski et al 2014 NF 54 023005

[2] M. Salewski et al 2013 NF 53 063019

[3] L. Stagner et al 2022 NF 62 026033

[4] B. Geiger et al 2020 PPCF 62 105008

[5] J Galdon-Quiroga et al 2018 PPCF 60 105005