A new compact solid-state neutral particle analyser at ASDEX Upgrade: Setup and physics modeling

Abstract

At ASDEX Upgrade (AUG), a new compact solid-state detector has been installed to measure the energy spectrum of fast neutrals based on the principle described by Shinohara et al. [Rev. Sci. Instrum. 75, 3640 (2004)]. The diagnostic relies on the usual charge exchange of supra-thermal fast-ions with neutrals in the plasma. Therefore, the measured energy spectra directly correspond to those of confined fast-ions with a pitch angle defined by the line of sight of the detector. Experiments in AUG showed the good signal to noise characteristics of the detector. It is energy calibrated and can measure energies of 40-200 keV with count rates of up to 140 kcps. The detector has an active view on one of the heating beams. The heating beam increases the neutral density locally; thereby, information about the central fast-ion velocity distribution is obtained. The measured fluxes are modeled with a newly developed module for the 3D Monte Carlo code F90FIDASIM [Geiger et al., Plasma Phys. Controlled Fusion 53, 65010 (2011)]. The modeling allows to distinguish between the active (beam) and passive contributions to the signal. Thereby, the birth profile of the measured fast neutrals can be reconstructed. This model reproduces the measured energy spectra with good accuracy when the passive contribution is taken into account.

Phase-space resolved measurement of 2nd harmonic ion cyclotron heating using FIDA tomography at the ASDEX Upgrade tokamak

“…This feature is regularly observed with the active neutral particle analyzer, and the reason behind this is not completely understood yet. All obvious diagnostic artifacts could be excluded to cause this measurement [46].…”

The effects of electron cyclotron heating and current drive on toroidal Alfvén eigenmodes in tokamak plasmas

“…Next, the possibility of ECRH-generated fast ions was investigated from the neutral particle analyser [23] measurements. No evidence was found for an ECRH-driven fast ion population in our discharges.…”

Enhancement of the FIDA diagnostic at ASDEX Upgrade for velocity space tomography

“…Fast ions can be studied e.g. with neutral particle analyzers [1], collective Thomson scattering [2] or with neutron yield measurements and spectroscopy [3,4]. In this paper, we want to focus on another possibility, which is the spectroscopic observation of line radiation (fast-ion D-alpha, FIDA) that emerges after charge exchange reactions [5].…”