Characterization of the Li-BES at ASDEX Upgrade

Willensdorfer, M.; Birkenmeier, G.; Fischer, R.; Laggner, F. M.; Wolfrum, E.; Veres, G. I.; Aumayr, F.; Carralero, D.; Guimarãis, L.; Kurzan, B.

doi:10.1088/0741-3335/56/2/025008

Cited by 77 publications

(107 citation statements)

References 37 publications

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“…8(b) and (d). This trend of larger uncertainties in the inner region is also observed in ASDEX Upgrade [7,24]. Here, we provide two qualitative reasons to explain this trend.…”

Section: Edge Electron Density Profilessupporting

confidence: 70%

“…It is evident that the former case has the larger uncertainty than the latter case even if the absolute numbers of the first excited state are the same for both cases. Therefore, the beam attenuation, i.e., decrease of the total number of beam atoms, can cause the larger uncertainty of n e in the inner region [24]. Finally, we note that there can be additional effects from the uncertainties of the absolute calibration factor [4,8].…”

Section: Edge Electron Density Profilesmentioning

confidence: 87%

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Bayesian electron density inference from JET lithium beam emission spectra using Gaussian processes

et al. 2017

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Abstract. A Bayesian model to infer edge electron density profiles is developed for the JET lithium beam emission spectroscopy (Li-BES) system, measuring Li I (2p-2s) line radiation using 26 channels with ∼ 1 cm spatial resolution and 10 ∼ 20 ms temporal resolution. The density profile is modelled using a Gaussian process prior, and the uncertainty of the density profile is calculated by a Markov Chain Monte Carlo (MCMC) scheme. From the spectra measured by the transmission grating spectrometer, the Li I line intensities are extracted, and modelled as a function of the plasma density by a multi-state model which describes the relevant processes between neutral lithium beam atoms and plasma particles. The spectral model fully takes into account interference filter and instrument effects, that are separately estimated, again using Gaussian processes. The line intensities are inferred based on a spectral model consistent with the measured spectra within their uncertainties, which includes photon statistics and electronic noise. Our newly developed method to infer JET edge electron density profiles has the following advantages in comparison to the conventional method: i) providing full posterior distributions of edge density profiles, including their associated uncertainties, ii) the available radial range for density profiles is increased to the full observation range (∼ 26 cm), iii) an assumption of monotonic electron density profile is not necessary, iv) the absolute calibration factor of the diagnostic system is automatically estimated overcoming the limitation of the conventional technique and allowing us to infer the electron density profiles for all pulses without preprocessing the data or an additional boundary condition, and v) since the full spectrum is modelled, the procedure of modulating the beam to measure the background signal is only necessary for the case of overlapping of the Li I line with impurity lines.

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“…8(b) and (d). This trend of larger uncertainties in the inner region is also observed in ASDEX Upgrade [7,24]. Here, we provide two qualitative reasons to explain this trend.…”

Section: Edge Electron Density Profilessupporting

confidence: 70%

Section: Edge Electron Density Profilesmentioning

confidence: 87%

Bayesian electron density inference from JET lithium beam emission spectra using Gaussian processes

et al. 2017

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“…In the confined region the density can be measured at the outboard midplane via lithium beam emission spectroscopy (LiBES) [24]. The magnetic signalḂ θ measured below the inner divertor target (C09-23) is correlated with the density perturbation measured in the very edge of the confined region (ρ pol = 0.99) as shown in comparison in Fig.…”

Section: Up-down Asymmetric Parallel Current Fluctuations During mentioning

confidence: 93%

Poloidal asymmetric flow and current relaxation of ballooned transport during I-phase in ASDEX Upgrade

et al. 2016

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Turbulence driven poloidal asymmetric parallel flow and current perturbations are studied for tokamak plasmas of circular geometry. Whereas zonal flows can lead to in-out asymmetry of parallel flows and currents via the Pfirsch-Schlüter mechanism, ballooned transport can result in an updown asymmetry due to the Stringer spin-up mechanism. Measurements of up-down asymmetric parallel current fluctuations occurring during the I-phase in ASDEX Upgrade are not responses to the equilibrium by the Pfirsch-Schlüter current, but can be interpreted as a response to strongly ballooned plasma transport coupled with the Stringer spin-up mechanism. A good agreement of the experimental measured limit-cycle frequencies during I-phase with the Stringer spin-up relaxation frequency is found.

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“…2(a),(b)) and toroidal ( Fig. 2(b)) positions of CXRS [36], LIB [37,38], ECE and ECE-imaging (ECE-I), which measure ion temperature (T i ), electron density (n e ) and T e , respectively. Additionally, the magnetic probes used for the equilibrium reconstruction and plasma position control are shown.…”

Section: Mp-coils and Edge Diagnosticsmentioning

confidence: 99%

Plasma response measurements of external magnetic perturbations using electron cyclotron emission and comparisons to 3D ideal MHD equilibrium

Willensdorfer

Denk

Strumberger

et al. 2016

Plasma Phys. Control. Fusion

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Abstract. The plasma response from an external n = 2 magnetic perturbation field in ASDEX Upgrade has been measured using mainly electron cyclotron emission (ECE) diagnostics and a rigid rotating field. To interpret ECE and ECE-imaging (ECE-I) measurements accurately, forward modeling of the radiation transport has been combined with ray tracing. The measured data is compared to synthetic ECE data generated from a 3D ideal magnetohydrodynamics (MHD) equilibrium calculated by VMEC.The measured amplitudes of the helical displacement around the low field side midplane are in reasonable agreement with the one from the synthetic VMEC diagnostics. Both exceed the prediction from the vacuum field calculations and indicate the presence of a kink response at the edge, which amplifies the perturbation. VMEC and MARS-F have been used to calculate the properties of this kink mode. The poloidal mode structure of the magnetic perturbation of this kink mode at the edge peaks at poloidal mode numbers larger than the resonant components |m| > |nq|, whereas the poloidal mode structure of its displacement is almost resonant |m| ≈ |nq|. This is expected from ideal MHD in the proximity of rational surfaces. The displacement measured by ECE-I confirms this resonant response.

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Characterization of the Li-BES at ASDEX Upgrade

Cited by 77 publications

References 37 publications

Bayesian electron density inference from JET lithium beam emission spectra using Gaussian processes

Bayesian electron density inference from JET lithium beam emission spectra using Gaussian processes

Poloidal asymmetric flow and current relaxation of ballooned transport during I-phase in ASDEX Upgrade

Plasma response measurements of external magnetic perturbations using electron cyclotron emission and comparisons to 3D ideal MHD equilibrium

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