8 research outputs found
Reducing systematic errors in time-frequency resolved mode number analysis
The present paper describes the effect of magnetic pick-up coil transfer
functions on mode number analysis in magnetically confined fusion plasmas.
Magnetic probes mounted inside the vacuum chamber are widely used to
characterize the mode structure of magnetohydrodynamic modes, as, due to their
relative simplicity and compact nature, several coils can be distributed over
the vessel. Phase differences between the transfer functions of different
magnetic pick-up coils lead to systematic errors in time- and frequency
resolved mode number analysis. This paper presents the first in-situ,
end-to-end calibration of a magnetic pick-up coil system which was carried out
by using an in-vessel driving coil on ASDEX Upgrade. The effect of the phase
differences in the pick-up coil transfer functions is most significant in the
50-250 kHz frequency range, where the relative phase shift between the
different probes can be up to 1 radian (~60{\deg}). By applying a correction
based on the transfer functions we found smaller residuals of mode number
fitting in the considered discharges. In most cases an order of magnitude
improvement was observed in the residuals of the mode number fits, which could
open the way to investigate weaker electromagnetic oscillations with even high
mode numbers
Experimental characterization of the active and passive fast-ion H-alpha emission in W7-X using FIDASIM
This paper presents the first results from the analysis of Balmer-alpha spectra at Wendelstein 7-X which contain the broad charge exchange emission from fast-ions. The measured spectra are compared to synthetic spectra predicted by the FIDASIM code, which has been supplied with the 3D magnetic fields from VMEC, 5D fast-ion distribution functions from ASCOT, and a realistic Neutral Beam Injection geometry including beam particle blocking elements. Detailed modeling of the beam emission shows excellent agreement between measured beam emission spectra and predictions. In contrast, modeling of beam halo radiation and Fast-Ion H-Alpha signals (FIDA) is more challenging due to strong passive contributions. While about 50% of the halo radiation can be attributed to passive signals from edge neutrals, the FIDA emissionâin particular for an edge-localized line of sightsâis dominated by passive emission. This is in part explained by high neutral densities in the plasma edge and in part by edge-born fast-ion populations as demonstrated by detailed modeling of the edge fast-ion distribution
Validating the ASCOT modelling of NBI fast ions in Wendelstein 7-X stellarator
The first fast ion experiments in Wendelstein 7-X were performed in 2018. They are one of the first steps in demonstrating the optimised fast ion confinement of the stellarator. The fast ions were produced with a neutral beam injection (NBI) system and detected with infrared cameras (IR), a fast ion loss detector (FILD), fast ion charge exchange spectroscopy (FIDA), and post-mortem analysis of plasma facing components. The fast ion distribution function in the plasma and at the wall is being modelled with the ASCOT suite of codes. They calculate the ionisation of the injected neutrals and the consecutive slowing down process of the fast ions. The primary output of the code is the multidimensional fast ion distribution function within the plasma and the distribution of particle hit locations and velocities on the wall. Synthetic measurements based on ASCOT output are compared to experimental results to assess the validity of the modelling. This contribution presents an overview of the various fast ion measurements in 2018 and the current modelling status. The validation and data-analysis is on-going, but the wall load IR modelling already yield results that match with the experiments
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The first fast ion experiments in Wendelstein 7-X were performed in 2018.
They are one of the first steps in demonstrating the optimised fast ion
confinement of the stellarator. The fast ions were produced with a neutral beam
injection (NBI) system and detected with infrared cameras (IR), a fast ion loss
detector (FILD), fast ion charge exchange spectroscopy (FIDA), and post-mortem
analysis of plasma facing components. The fast ion distribution function in the
plasma and at the wall is being modelled with the ASCOT suite of codes. They
calculate the ionisation of the injected neutrals and the consecutive slowing
down process of the fast ions. The primary output of the code is the
multidimensional fast ion distribution function within the plasma and the
distribution of particle hit locations and velocities on the wall. Synthetic
measurements based on ASCOT output are compared to experimental results to
assess the validity of the modelling. This contribution presents an overview of
the various fast ion measurements in 2018 and the current modelling status. The
validation and data-analysis is on-going, but the wall load IR modelling
already yield results that match with the experiments.Comment: Presented in the 3rd European Conference on Plasma Diagnostics; 6th
to 9th of May 2019; Lisbon, Portuga
Validation of the BEAMS3D neutral beam deposition model on Wendelstein 7-X
| openaire: EC/H2020/633053/EU//EUROfusionThe neutral beam deposition model in the BEAMS3D code is validated against neutral beam attenuation data from Wendelstein 7-X (W7-X). A set of experimental discharges where the neutral beam injection system of W7-X was utilized were reconstructed. These discharges scanned the magnetic configurations and plasma densities of W7-X. The equilibrium reconstructions were performed using STELLOPT which calculates three-dimensional self-consistent ideal magnetohydrodynamic equilibria and kinetic profiles. These reconstructions leveraged new capabilities to incorporate electron cyclotron emission and X-ray imaging diagnostics in the STELLOPT code. The reconstructed equilibria and profiles served as inputs for BEAMS3D calculations of neutral beam deposition in W7-X. It is found that if reconstructed kinetic profiles are utilized, good agreement between measured and simulated beam attenuation is found. As deposition models provide initial conditions for fast-ion slowing down calculations, this work provides a first steptowards validating our ability to predict fast ion confinement in stellarators.Peer reviewe