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

@article{Chilenski2015ImprovedPF,
  title={Improved profile fitting and quantification of uncertainty in experimental measurements of impurity transport coefficients using Gaussian process regression},
  author={M. A. Chilenski and Martin Greenwald and Youssef M. Marzouk and N. T. Howard and Anne E. White and John E Rice and J. R. Walk},
  journal={Nuclear Fusion},
  year={2015},
  volume={55}
}
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… 

Inference of experimental radial impurity transport on Alcator C-Mod: Bayesian parameter estimation and model selection

We present a fully Bayesian approach for the inference of radial profiles of impurity transport coefficients and compare its results to neoclassical, gyrofluid and gyrokinetic modeling. Using nested

Experimentally testing the dependence of momentum transport on second derivatives using Gaussian process regression

It remains an open question to explain the dramatic change in intrinsic rotation induced by slight changes in electron density (White et al 2013 Phys. Plasmas 20 056106). One proposed explanation is

Estimation and Uncertainties of Profiles and Equilibria for Fusion Modeling Codes

Two different techniques are presented to estimate profiles, profile gradients, their uncertainties, and candidate profiles for UP in modeling codes for plasma transport and stability codes.

Efficient design and verification of diagnostics for impurity transport experiments.

A fast, linearized model was constructed to estimate diagnostic requirements for impurity transport experiments and shows that the spectroscopic diagnostics on Alcator C-Mod should be capable of inferring simple profiles of impurity diffusion DZ and convection VZ accurate to better than ±10% uncertainty.

An Improved Approach to Uncertainty Quantification for Plasma Turbulence Validation Studies

Abstract Due to the strong nonlinear dependence of plasma turbulence on drive and dissipation mechanisms, uncertainties in experimental inputs can be greatly magnified in simulations of this

Plasma parameter profile inference from limited data utilizing second-order derivative priors and physic-based constraints

A new profile inference framework is proposed that utilizes prior knowledge about plasma physics, along with integrated data analysis and a Gaussian process to facilitate the use of the Markov chain Monte Carlo sampling and define quantities corresponding to the second derivatives of the profiles.

Experimental inference of neutral and impurity transport in Alcator C-Mod using high-resolution x-ray and ultra-violet spectra

We present experimental inferences of cross-field impurity transport coefficients for AlcatorC-Mod plasmas without edge-localized modes, leveraging a novel forward model for the entire Ca K α

On the importance of model selection when inferring impurity transport coefficient profiles

We present an analysis which suggests that model selection is a critical ingredient for successful reconstruction of impurity transport coefficient profiles, D and V, from experimental data.

Experimental and modeling uncertainties in the validation of lower hybrid current drive

This work discusses sources of uncertainty in the validation of lower hybrid wave current drive simulations against experiments, by evolving self-consistently the magnetic equilibrium and the heating

Inference of temperature and density profiles via forward modeling of an x-ray imaging crystal spectrometer within the Minerva Bayesian analysis framework.

The inversion method shows a correct and reliable inference of temperature and impurity density profiles from synthesized data within the estimated uncertainties along the whole plasma radius.
...

References

SHOWING 1-10 OF 73 REFERENCES

Measurement of plasma current dependent changes in impurity transport and comparison with nonlinear gyrokinetic simulationa)

Measured impurity transport coefficients are found to demonstrate a strong dependence on plasma current in the core of Alcator C-Mod. These measurements are compared directly with linear and

Experimental and gyrokinetic studies of impurity transport in the core of Alcator C-Mod Plasmas

Using a unique set of diagnostics and modeling tools, a comprehensive study of impurity transport was performed on Alcator C-Mod L-mode discharges. A new, multipulse laser blow-off system was

Non-parametric profile gradient estimation

The aim is to have a robust technique to allow for a reasonable balance between flexibility and reliability, e.g. linear interpolation between pointwise estimations or cubic or B-splines.

Quantitative comparison of experimental impurity transport with nonlinear gyrokinetic simulation in an Alcator C-Mod L-mode plasma

Nonlinear gyrokinetic simulations of impurity transport are compared to experimental impurity transport for the first time. The GYRO code (Candy and Waltz 2003 J. Comput. Phys. 186 545) was used to

Multiple diagnostic data analysis of density and temperature profiles in ASDEX Upgrade

The Integrated Data Analysis approach provides a full probabilistic model including physical and statistical description of an integrated set of different diagnostics to study the fast temporal evolution of density, temperature and pressure profiles for inter-ELM phases as well as ELM resolved.

Potential of a Bayesian Integrated Determination of the Ion Effective Charge via Bremsstrahlung and Charge Exchange Spectroscopy in Tokamak Plasmas

Reliable and accurate estimates of the ion effective charge Zeff in tokamak plasmas are of key importance with respect to the impurity transport studies and the establishment of thermonuclear burn

Implementation and application of two synthetic diagnostics for validating simulations of core tokamak turbulence

The deployment of multiple high-resolution, spatially localized fluctuation diagnostics on the DIII-D tokamak [J. L. Luxon, Nucl. Fusion 42, 614 (2002)] opens the door to a new level of core

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

The knowledge of the effective ion charge Zeff which indicates the degree of plasma pollution is of high interest, since the tolerable impurity concentration to achieve successful ignition of a

Integrated density profile analysis in ASDEX Upgrade H-modes

The method of Integrated Data Analysis (IDA) provides a full probabilistic model including physical and statistical models of an integrated set of different diagnostics. The goal of IDA is to combine

Steps towards an integrated data analysis: Basic concepts and Bayesian analysis of Thomson scattering data

Investigations start with a rigorous error analysis of data and explore possibilities for integration of available physics information in order to enhance the significance and the reliability of experimental data from fusion devices.
...