Quantification of the impact of large and small-scale instabilities on the fast-ion confinement in ASDEX Upgrade

Geiger, B.; Weiland, M.; Mlynek, A.; Reich, M.; Bock, A.; Dunne, M.; Dux, R.; Fable, E.; Fischer, R.; García-Muñoz, M.; Hobirk, J.; Hopf, C.; Nielsen, S. K.; Odstrčil, T.; Rapson, C.; Rittich, D.; Ryter, F.; Salewski, M.; Schneider, P. A.; Tardini, G.; Willensdorfer, M.

doi:10.1088/0741-3335/57/1/014018

Cited by 30 publications

(48 citation statements)

References 38 publications

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“…This is particularly obvious for the FIDA measurements, which tend to exceed the baseline prediction at the 1σ measurement uncertainties. While examples of good agreement between FIDA measurements and TRANSP predictions exist at both AUG [9][10][11] and DIII-D [29], there are also some AUG discharges for which the simulated FIDA profile lies ∼ 30% below measurements [5] as seen here. This has been ascribed to uncertainties in the FIDA intensity calibration and in the atomic transition rates and charge exchange cross sections implemented in the FIDASIM code.…”

Section: Discussionsupporting

confidence: 58%

Consistency between real and synthetic fast-ion measurements at ASDEX Upgrade

Rasmussen

Nielsen

Stejner

et al. 2015

Plasma Phys. Control. Fusion

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Abstract. Internally consistent characterization of the properties of the fastion distribution from multiple diagnostics is a prerequisite for obtaining a full understanding of fast-ion behavior in tokamak plasmas. Here we benchmark several absolutely-calibrated core fast-ion diagnostics at ASDEX Upgrade by comparing fastion measurements from collective Thomson scattering, fast-ion D α spectroscopy, and neutron rate detectors with numerical predictions from the TRANSP/NUBEAM transport code. We also study the sensitivity of the theoretical predictions to uncertainties in the plasma kinetic profiles. We find that theory and measurements generally agree within these uncertainties for all three diagnostics during heating phases with either one or two neutral beam injection sources. This suggests that the measurements can be described by the same model assuming classical slowing down of fast ions. Since the three diagnostics in the adopted configurations probe partially overlapping regions in fast-ion velocity space, this is also consistent with good internal agreement among the measurements themselves. Hence, our results support the feasibility of combining multiple diagnostics at ASDEX Upgrade to reconstruct the fast-ion distribution function in 2D velocity space.

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Section: Discussionsupporting

confidence: 58%

Consistency between real and synthetic fast-ion measurements at ASDEX Upgrade

Rasmussen

Nielsen

Stejner

et al. 2015

Plasma Phys. Control. Fusion

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“…Furthermore, the FIDA diagnostic has been extended from three to five viewing arrays for a better coverage of the velocity space. First results from the new spectrometer setup and four FIDA views have been shown already in [9]. The details of the diagnostic improvements are now described in this paper in section 2.…”

Section: Introductionmentioning

confidence: 99%

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

Weiland

Geiger

Jacobsen

et al. 2016

Plasma Phys. Control. Fusion

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Recent upgrades to the FIDA (fast-ion D-alpha) diagnostic at ASDEX Upgrade are discussed: The diagnostic has been extended from three to five line of sight arrays with different angles to the magnetic field, and a spectrometer redesign allows the simultaneous measurement of red-and blue-shifted parts of the Doppler spectrum. These improvements make it possible to reconstruct the 2D fast-ion velocity distribution f (E, v /v) from the FIDA measurements by tomographic inversion under a wide range of plasma parameters. Two applications of the tomography are presented: A comparison between the distributions resulting from 60 keV and 93 keV NBI and a velocity-space resolved study of fast-ion redistribution induced by a sawtooth crash inside and outside the sawtooth inversion radius.

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“…6. Fast-ion pressure profiles redistributed after the sawtooth event using particle conservation and a 50 ms recovery time The magnetic reconnection induced by sawtooth events are known to transport fast ions 52,53 . Fast-ion D-alpha (FIDA) measurements show a significant reduction of the central fast-ion density along with an increase at larger radii.…”

Section: Va Pressure Profiles and Fast-ion Redistributionmentioning

confidence: 99%

“…Fast-ion D-alpha (FIDA) measurements show a significant reduction of the central fast-ion density along with an increase at larger radii. Simultaneously, the loss of fast particles, detected by a fast-ion loss detector (FILD) outside of the plasma 52 and by comparing measured and modelled neutron rates 53 , is marginal. The fast-ion density profile reconstructed from the FIDA measurements shows a depletion zone within the inversion radius and an enrichment up to the mixing radius 53 .…”

Section: Va Pressure Profiles and Fast-ion Redistributionmentioning

confidence: 99%

Sawtooth inducedq-profile evolution at ASDEX Upgrade

Fischer¹,

Bock²,

Burckhart³

et al. 2019

Nucl. Fusion

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The sawtooth induced q-profile evolution was modelled at ASDEX Upgrade and validated with imaging motional Stark effect (IMSE) measurements. The equilibrium current distribution was estimated by the coupling of a Grad-Shafranov solver and the current diffusion equation. At ASDEX Upgrade an extensive diagnostic suite allows for a reliable modelling of the current density profile and its temporal evolution as long as neo-classical current diffusion can be assumed. The sawtooth-induced central q change, ∆q 0 , was estimated from equilibrium reconstruction between the sawtooth events without using IMSE measurements. The sawtooth-induced current relaxation is modelled with two different reconnection models, a Kadomtsev full reconnection and a newly developed fully stochastic flat-current model. Both models result in about the same sawtooth-induced ∆q 0 ≈ 0.10-0.12 but with a small difference in the absolute q 0 values. The sawtooth-induced evolution of the forward modelled MSE angles agrees well with the IMSE measurements. This confirms the assumption of neoclassical current diffusion between the sawtooth events. A sensitivity study reveals two major ingredients for a reliable interpretation of MSE measurements. Firstly, the sawtooth-induced redistribution of fast ions has to be taken into account for a reliable estimation of the Shafranov shift. The fast-ion redistribution is modelled with a particle-conserving homogeneous fast-ion pressure profile in the plasma core and a subsequent recovery time of 50 ms. Secondly, a reliable estimation of the electric field is necessary for a credible interpretation of the MSE angles.

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Quantification of the impact of large and small-scale instabilities on the fast-ion confinement in ASDEX Upgrade

Cited by 30 publications

References 38 publications

Consistency between real and synthetic fast-ion measurements at ASDEX Upgrade

Consistency between real and synthetic fast-ion measurements at ASDEX Upgrade

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

Sawtooth inducedq-profile evolution at ASDEX Upgrade

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