Forward modeling of collective Thomson scattering for Wendelstein 7-X plasmas: Electrostatic approximation

Abramovic, I.; Pavone, A.; Moseev, D.; Cardozo, N.J. Lopes; Salewski, M.; Laqua, H. P.; Stejner, M.; Stange, T.; Marsen, S.; Nielsen, S. K.; Jensen, Thomas; Kasparek, W.; Team, W X

doi:10.1063/1.5048361

Cited by 11 publications

(13 citation statements)

References 35 publications

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“…The horizontal lines show the median values of χ 2 red : 26.8, 1.9, and 1.2 for equivalent noise levels of 1%, 10%, and 100%, respectively. For measurements with a low error in their category, the values of χ 2 red are distributed around a value slightly larger than one, indicating a modest underfit of mapping to data. = 10%, and 2 < n D /n e < 1.…”

Section: Fig 6 Scatter Plots Of χmentioning

confidence: 97%

“…In the eCTS code, the spectral density function is calculated in the electrostatic approximation, where only the scattering off of fluctuations in the electron density is taken into account. 2 The spectral density function is given by 18 S k δ , ω = S e k δ , ω…”

Section: A Collective Thomson Scattering On W7-xmentioning

confidence: 99%

“…20 χ 2 red has an intrinsic probability distribution function, which can only be known for the true model having the true parameter values. χ 2 red can still provide an indication of self-consistency: under the assumption that the approximation (be it FP or a neural network) follows the true model, χ 2 red of the most accurate measurements should follow the χ 2 red -distribution and thus have a mean value of 1. Moreover, a correlation between and χ 2 red might provide a rough error estimation for measurements.…”

Section: Error Analysismentioning

confidence: 99%

“…To describe the scattering process and compute the scattered spectra, the forward code eCTS is available. 2 For the interpretation of measured spectra, the eCTS code is integrated a) JvandenBerg@pm.me in the generic Bayesian data analysis framework Minerva, implemented at W7-X. 3 However, finding the best fit using the eCTS code requires many runs, which takes up to several minutes of computation per spectrum.…”

Section: Introductionmentioning

confidence: 99%

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Fast analysis of collective Thomson scattering spectra on Wendelstein 7-X

Berg

Abramovic

Cardozo

et al. 2018

Review of Scientific Instruments

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Two methods for fast analysis of Collective Thomson Scattering (CTS) spectra are presented: Function Parametrization (FP) and feedforward Artificial Neural Networks (ANNs). At this time, a CTS diagnostic is being commissioned at the Wendelstein 7-X (W7-X) stellarator, with ion temperature measurements in the plasma core as its primary goal. A mapping was made from a database of simulated CTS spectra to the corresponding ion and electron temperatures ( and ). The mean absolute mapping errors are 4.2% and 9.9% relative to the corresponding , for the ANN and FP, respectively, for spectra with Gaussian noise equivalent to 10% of the average of the spectral maxima in the database at 650 sampling points per GHz and within a limited parameter space. Although FP provides some insight into the information contents of the CTS spectra, ANNs provide a higher accuracy and noise robustness, are easier to implement, and are more adaptable to a larger parameter space. These properties make ANN mappings a promising all-round method for fast CTS data analysis. Addition of impurity concentrations to the current parameter space will enable fast bulk ion temperature measurements in the plasma core region of W7-X.

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Section: Fig 6 Scatter Plots Of χmentioning

confidence: 97%

Section: A Collective Thomson Scattering On W7-xmentioning

confidence: 99%

Section: Error Analysismentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Fast analysis of collective Thomson scattering spectra on Wendelstein 7-X

Berg

Abramovic

Cardozo

et al. 2018

Review of Scientific Instruments

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“…The possibilities of CTS were demonstrated experimentally at TFTR [3], JET [4], TEXTOR [5,6], ASDEX-U [7,8] tokamaks for diagnosing the distribution function of fast ions, at W7-AS stellarator for diagnosing the temperature of thermal ions and the lower hybrid plasma instability [9][10][11], at LHD stellarator for measurement of both fast and thermal ions [12,13], and, most recently, at the newest W7-X stellarator for diagnosing the temperature of thermal ions [14,15].…”

Section: Introductionmentioning

confidence: 99%

Collective Thomson scattering diagnostic for the GDT open magnetic trap

Shalashov

Gospodchikov

Khusainov

et al. 2020

Plasma Phys. Control. Fusion

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In this paper, we propose a collective Thomson scattering diagnostic for fast ion measurements for the gas-dynamic trap (GDT) facility at the Budker Institute. The diagnostic utilizes 54.5 GHz gyrotron usually used for electron cyclotron resonance heating as a source of probe radiation and is aimed at reconstruction of distributions over transverse and longitudinal velocities of NBIdriven ions in the plasma core. Here we present a feasibility study of this concept showing a possibility to receive a strong CTS signal of hundreds eVs for a wide range of GDT parameters. The main limitations come from the refraction of the probe and scattered radiation propagating in inhomogeneous plasma: to provide well-resolved CTS conditions the on-axis plasma density should be kept less than 1.5 · 10 13 cm −3 while usual GDT discharges correspond to the density of (0.9 − 1.3) · 10 13 cm −3 .

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Collective Thomson scattering model for arbitrarily drifting bi-Maxwellian velocity distributions

2019

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In this paper we derive the equations of collective Thomson scattering (CTS) for an arbitrarily drifting magnetized plasma described by a bi-Maxwellian distribution. The model allows the treatment of anisotropic plasma with different parallel and perpendicular temperatures (with respect to the magnetic field) as well as parallel and perpendicular plasma drift. As could be expected, parallel observation directions are most sensitive to the parallel temperature and drift, whereas perpendicular observation directions are most sensitive to the perpendicular temperature and the perpendicular drift along the observation direction. The perpendicular drift can be related to the radial electric field. Measurements with a spectral resolution better than 0.5 MHz are necessary for the inference of the radial electric field. This spectral resolution and the required scattering geometry are attainable with the current setup of the CTS diagnostic on Wendelstein 7-X.

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Forward modeling of collective Thomson scattering for Wendelstein 7-X plasmas: Electrostatic approximation

Abstract: A high-quality and energy-tunable positronium beam system employing a trap-based positron beam Review of Scientific Instruments 90, 023305 (2019);

Cited by 11 publications

References 35 publications

Fast analysis of collective Thomson scattering spectra on Wendelstein 7-X

Fast analysis of collective Thomson scattering spectra on Wendelstein 7-X

Collective Thomson scattering diagnostic for the GDT open magnetic trap

Collective Thomson scattering model for arbitrarily drifting bi-Maxwellian velocity distributions

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