Estimation of profiles of the effective ion charge at ASDEX Upgrade with Integrated Data Analysis

Rathgeber, S. K.; Fischer, R.; Fietz, S.; Hobirk, J.; Kallenbach, A.; Meister, H.; Pütterich, T.; Ryter, F.; Tardini, G.; Wolfrum, E.

doi:10.1088/0741-3335/52/9/095008

Cited by 61 publications

(69 citation statements)

References 23 publications

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“…Two Thomson scattering (TS) systems are used to measure the n e , T e profiles in the core and the edge, and three separate electron cyclotron emission (ECE) systems are used to further constrain the core T e profile. For the discharge analyzed here, Calcium (a non-intrinsic, [46,47,48]), in which case even these steps are absorbed into the IDA step.…”

Section: Application Of Gpr To Alcator C-mod Profilesmentioning

confidence: 99%

Improved profile fitting and quantification of uncertainty in experimental measurements of impurity transport coefficients using Gaussian process regression

Chilenski¹,

Greenwald²,

Marzouk³

et al. 2015

Nucl. Fusion

113

122

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Abstract. The need to fit smooth temperature and density profiles to discrete observations is ubiquitous in plasma physics, but the prevailing techniques for this have many shortcomings that cast doubt on the statistical validity of the results. This issue is amplified in the context of validation of gyrokinetic transport models (Holland et al. 2009, Phys. Plasmas 16, 052301), where the strong sensitivity of the code outputs to input gradients means that inadequacies in the profile fitting technique can easily lead to an incorrect assessment of the degree of agreement with experimental measurements. In order to rectify the shortcomings of standard approaches to profile fitting, we have applied Gaussian process regression (GPR), a powerful nonparametric regression technique, to analyze an Alcator C-Mod L-mode discharge used for past gyrokinetic validation work , Nucl. Fusion 52, 063002). We show that the GPR techniques can reproduce the previous results while delivering more statistically rigorous fits and uncertainty estimates for both the value and the gradient of plasma profiles with an improved level of automation. We also discuss how the use of GPR can allow for dramatic increases in the rate of convergence of uncertainty propagation for any code that takes experimental profiles as inputs. The new GPR techniques for profile fitting and uncertainty propagation are quite useful and general, and we describe the steps to implementation in detail in this paper. These techniques have the potential to substantially improve the quality of uncertainty estimates on profile fits and the rate of convergence of uncertainty propagation, making them of great interest for wider use in fusion experiments and modeling efforts.

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Section: Application Of Gpr To Alcator C-mod Profilesmentioning

confidence: 99%

Improved profile fitting and quantification of uncertainty in experimental measurements of impurity transport coefficients using Gaussian process regression

Chilenski¹,

Greenwald²,

Marzouk³

et al. 2015

Nucl. Fusion

113

122

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“…In the discharges presented here, no direct ion heating was applied and the ion heat flux is purely due to the electron-ion collisional exchange. The electron density (n e ), the radiation power density (p rad ) and the Z eff profiles are based on measured data, [25], [26] and [27] respectively. No ion temperature measurements are available in these ramp-up studies and the T i profile is calculated using the neoclassical ion diffusivity, [28,29].…”

Section: Transport Modellingmentioning

confidence: 99%

“…At ASDEX Upgrade the Z eff profiles are provided by the integrated data analysis (IDA), which includes the data from the bremsstrahlung measurements, [27]. The uncertainties on Z eff are about 20 % in the core and larger at the edge.…”

Section: Sensitivity Of L I (3) On the Z Eff Profilementioning

confidence: 99%

Investigation of transport models in ASDEX Upgrade current ramps

et al. 2013

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Abstract.Understanding the physics of transport during current ramps in tokamaks is essential in order to prepare adequate ramp-up and ramp-down scenarios for ITER, where constraints on the transformer flux and the internal inductance will be more stringent than in present-day devices. In this paper five transport models (CoppiTang, Neo-Alcator, Bohm/gyro-Bohm, critical gradient model and H98/2 scalingbased model) are used to reproduce the experimental data during the current ramps of ASDEX Upgrade with its metallic wall. The calculated temperature profiles are compared to the experimental temperature profiles under different ramp-up conditions. Our study reveals important differences between boronised and non boronised wall which are reproduced with variable success by the models. We also investigated rampup phases heated centrally by electron cyclotron heating which creates experimental conditions with peaked electron temperature profiles, which are very different from the usual ohmic heated cases. Our study reveals that the models react very differently to this additional heating.

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“…The uncertainties of the estimated parameters were calculated, based on the curvature of the posterior PDF at the maximum as described in [3]. A practical application of this method can be found for example in [4]. The logarithm L = log p (M (x) |d, I) of the posterior PDF is expanded in a Tailor series at the maximum, where the quadratic term is dominant.…”

Section: Fitting Of the Spectramentioning

confidence: 99%

Evaluation of Ion Temperature and Plasma Rotation at LHD from Charge-Exchange Spectra with Photon-Statistical Weighting

Wieland

Ida

Yoshinuma

2013

Plasma and Fusion Research

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A new diagnostic for LHD is presented, which utilizes active charge-exchange signals from Hydrogen (main ions) and Helium (impurity ions) to derive the radial ion-temperature and ion-velocity profiles as well as the H/He ratio profile. In a sensitivity study, different models for profile fitting and measurement uncertainties are compared, which leads to first results. This covers fitting with one Gauss function and two Gauss functions as well as the inclusion of read-out noise and photon noise. Full error propagation from the measured spectra to the resulting profiles is provided by utilizing Bayesian statistics in combination with a weighted least-squares fit and boundary conditions. Reliable and accurate results were achieved for the ion-temperature profiles, which are in good agreement with the well-proven Carbon diagnostic. Concerning the quality of the velocity profiles, no statement could be made. The H/He ratio measurements in contrary lead to accurate results. Calibration with the H/He ratio of passive emission near the plasma edge just before the end of the discharge allows calculating absolute values for Helium and Hydrogen density profiles.

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Estimation of profiles of the effective ion charge at ASDEX Upgrade with Integrated Data Analysis

Cited by 61 publications

References 23 publications

Improved profile fitting and quantification of uncertainty in experimental measurements of impurity transport coefficients using Gaussian process regression

Improved profile fitting and quantification of uncertainty in experimental measurements of impurity transport coefficients using Gaussian process regression

Investigation of transport models in ASDEX Upgrade current ramps

Evaluation of Ion Temperature and Plasma Rotation at LHD from Charge-Exchange Spectra with Photon-Statistical Weighting

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