Modelling of the NBI contribution to the neutron energy spectra for the ITER Vertical Neutron Camera

TL;DR

This paper presents a simulation-based analysis of neutron spectra for the ITER Vertical Neutron Camera, highlighting its capability to measure fuel ratio and observe plasma phenomena through detailed spectral modeling.

Contribution

It introduces a new software tool for simulating neutron spectra from suprathermal ion interactions, aiding in plasma diagnostics for ITER.

Findings

Fast D ions dominate neutron flux above 16 MeV

Fuel ratio can be assessed from thermal-thermal and beam-thermal spectra

VNC can potentially observe sawtooth-induced mixing

Abstract

The ITER Vertical Neutron Camera (VNC) is a multichannel collimator system designed to measure the neutron emissivity profile and spectra. The energy spectrum measurements of neutrons made by the VNC will contribute to the reconstruction of the ion temperature, fuel ratio, and fast ion distribution function. In this paper, the results of neutron spectra calculations for the ITER VNC are presented. The developed software allows for the simulation of particle spectra resulting from interaction of suprathermal ions with thermal background plasma. The method relies on direct reaction rate calculation and explicit fusion reaction kinematics modelling. The assessment of the D-T neutron spectra is carried out for D-NBI heated baseline D-T ITER operation scenarios. It is shown that neutron flux resulting from fast (beam) D with thermal T ion interaction dominates at more than 16 MeV part of the spectra. Thus, it is possible to assess fuel ratio based on calculated thermal-thermal and beam-thermal neutron energy spectra. An ability to observe sawtooth-induced mixing via VNC is studied. Lower energy boundary for the observable part of the suprathermal ion distribution is derived.