Velocity-space sensitivity of neutron spectrometry measurements

Abstract

Neutron emission spectrometry (NES) measures the energies of neutrons produced in fusion reactions. Here we present velocity-space weight functions for NES and neutron yield measurements. Weight functions show the sensitivity as well as the accessible regions in velocity space for a given range of the neutron energy spectrum. Combined with a calculated fast-ion distribution function, they determine the part of the distribution function producing detectable neutrons in a given neutron energy range. Furthermore, we construct a forward model based on weight functions capable of rapidly calculating neutron energy spectra. This forward model can be inverted and could thereby be used to directly measure the fast-ion phase-space distribution functions, possibly in combination with other fast-ion diagnostics. The presented methods and results can be applied to neutron energy spectra measured by any kind of neutron spectrometer and to any neutron yield measurement.

Fast-ion transport and neutral beam current drive in ASDEX upgrade

“…This suggests that the Kadomtsev model describes the sawtooth-induced fast-ion redistribution well. However, it should be noted that the neutron fluxes are dominated by specific parts of the fast-ion phase space [33] and no strong and global statement can be made here.…”

Fast ion energy distribution from third harmonic radio frequency heating measured with a single crystal diamond detector at the Joint European Torus

“…• -110 • ) and can be used to investigate whether a signature of the predicted 38,39 phase space sensitivity of the oblique SDD line of sight to ions with pitch angles away from 90…”

High-definition velocity-space tomography of fast-ion dynamics

“…The 2D velocity distribution function is spatially localized in a small measurement volume which we take to be a single point in position space. The fast-ion measurements depend on phase space in a complicated way illustrated by so-called weight functions which have been formulated for FIDA [10,32], neutral particle analyzers (NPA) [10], CTS [21], fast-ion loss detectors [33], NES [34,35] and GRS [36,37]. To exploit the rich information about fast ions contained in the measurements by traditional procedures, we need to consider hundreds of data points, e.g.…”