Application of Bayesian tomography method to the visible spectroscopic diagnostic on HL-2A tokamak

Liu, Dong; Liu, Liang; Svensson, J.; Wang, Tianbo; Li, Jiaxian; He, Xiaoxue; Shi, Z.B.; Xu, M.

doi:10.1088/1361-6587/abd0a3

Cited by 4 publications

(4 citation statements)

References 37 publications

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“…In view of the high pixel count of n p > 2000 and much fewer available signals (n l = 65), the tomography inversion turns into a poorly conditioned (underdetermined) problem. To solve such ill-posed problems, regularization techniques such as maximum entropy [47], Gaussian tomography [48], and MFR [34] have been widely applied. The MFR method was initially chosen for the W7-X bolometer tomography because of its advantages over other methods [49].…”

Section: The Optimization and The Physical Constraintsmentioning

confidence: 99%

Bolometer tomography on Wendelstein 7-X for study of radiation asymmetry

et al. 2021

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The algorithm for bolometer tomography at Wendelstein 7-X (W7-X) has been recently improved using a novel regularization functional, based on relative gradient smoothing of the sought radiation profile. It has been validated using radiation patterns provided by 3D modeling under real plasma conditions as phantoms and then applied to bolometer measurements performed during the first divertor operation phase of W7-X. The following results are presented: (1) edge-localized 2D radiation patterns with clearly resolved magnetic island radiation structures, (2) an up-down asymmetry in the impurity radiation that is not captured by the 3D edge plasma transport modeling, (3) reversal of the asymmetry with reversed magnetic field direction. Further analysis reveals a poloidal variation of the emissivity in the outer confined plasma region with a field-direction dependent asymmetry, also supported by the soft x-ray measurements. This asymmetry is considered to be related to asymmetric impurity distributions, driven by the pronounced ion-impurity friction force at the plasma edge where the collisionality of the W7-X plasma is sufficiently high to develop impurity asymmetry as predicted by neoclassical theory of parallel impurity transport.

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Section: The Optimization and The Physical Constraintsmentioning

confidence: 99%

Bolometer tomography on Wendelstein 7-X for study of radiation asymmetry

et al. 2021

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“…It is also possible to use Bayesian methods to infer the static visible light emissivity profile instead of the x-ray emissivity profiles discussed above. This is demonstrated in [13] where the visible light emissivity of the HL-2A tokamak is inferred using a Bayesian GP. The primary contribution of this work is a method to enforce the constraint that the emissivity must be a positive distribution through truncation of the prior.…”

Section: Prior Workmentioning

confidence: 99%

“…In this document we discussed only the uninformative Gaussian and CAR priors. Alternative priors do exist such as the GP prior, which provides another method to enforce the smoothness of the current density [13,32]. However, the application of these alternative priors to perturbed current tomography has not yet been explored in sufficient detail to warrant their inclusion here and instead we consider this to be an avenue for further research.…”

Section: Further Workmentioning

confidence: 99%

A Bayesian formulation for perturbed current tomography in tokamaks

Bohlsen,

Hole

2023

Plasma Phys. Control. Fusion

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An initial investigation into the application of Bayesian inference to the reconstruction of the spatial distribution of current perturbations in tokamaks from diagnostic signals is presented. Previous work in Bayesian equilibrium current tomography is extended to the case of a complex phasor representation of harmonically time varying current distributions. A forward function to predict the response of magnetic diagnostics is constructed using only electrodynamics and not reduced models of ideal MHD. The extension of this forward function to incorporate a fully kinetic model of the plasma state is suggested. The response of soft x-ray diagnostics, and the Motional Stark Effect diagnostic to the current perturbations are also predicted and the integration of all diagnostics into a single estimate of the current perturbation is proposed. Simulations with synthetic diagnostics in simple geometry demonstrate that the perturbed current distribution can be reconstructed subject to prior assumptions regarding solution smoothness.

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“…We have to admit that it could give extra information and lead to a certain bias in the end, but this application was aimed to deliver real-time capability. For more accurate inference, a truncated sampling technique should be put into scope in off-line analysis applications [26]. For the case of the HL-2A bolometer, the reconstruction of a single time slice takes about 3 ms with a typical single-core PC.…”

Section: Gpt With Magnetic Equilibrium Informationmentioning

confidence: 99%

Monitoring of two-dimensional tungsten concentration profiles on the HL-2A tokamak

Wang¹,

Li²,

Gao³

et al. 2022

Plasma Phys. Control. Fusion

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In this article, we demonstrate the inference of two-dimensional tungsten concentration profiles in tokamak plasmas, using Gaussian process tomography applied to bolometry and assuming a specific model for the tungsten cooling factor. In ITER, tungsten has been selected for divertor material due to its low tritium retention and ability to handle large heat and particle flux loads. On the other hand, this will cause tungsten impurities to enter the bulk plasma through various plasma-wall interaction processes. Therefore, a detailed understanding of tungsten impurity transport and active control of the impurity transport in tokamaks is crucial. The computational complexity of the method described in there article O(n2m) compares favorably to a simple least-squares approach O(n3), n represents the number of pixels and m the number of measurement channels, hence bringing real-time tungsten profile monitoring within reach (< 10 ms repetition time). The feasibility study of this method has been demonstrated here to a discharge in HL-2A for observing the entire process of tungsten impurities entering the bulk plasma from the scrape-off layer area, tungsten pump-out by edge-localized modes, as well as the formation of a poloidally asymmetric tungsten distribution.

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Application of Bayesian tomography method to the visible spectroscopic diagnostic on HL-2A tokamak

Cited by 4 publications

References 37 publications

Bolometer tomography on Wendelstein 7-X for study of radiation asymmetry

Bolometer tomography on Wendelstein 7-X for study of radiation asymmetry

A Bayesian formulation for perturbed current tomography in tokamaks

Monitoring of two-dimensional tungsten concentration profiles on the HL-2A tokamak

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