Non-axisymmetric equilibrium reconstruction of a current-carrying stellarator using external magnetic and soft x-ray inversion radius measurements

Ma, X.; Maurer, D.A.; Knowlton, S.; ArchMiller, M.C.; Cianciosa, M.; Ennis, D.A.; Hanson, J.D.; Hartwell, G.J.; Hebert, J.D.; Herfindal, J. L.; Pandya, M. D.; Roberds, Nicholas; Traverso, P.

doi:10.1063/1.4938031

Cited by 8 publications

(3 citation statements)

References 23 publications

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“…namely the Compact Toroidal Hybrid (CTH) [8,9], the National Compact Stellarator Experiment (NCSX) [10], the Helically Symmetric Experiment (HSX) [11][12][13], Wendelstein 7-AS (W7-AS) [14], and W7-X [4,15,16]. Moreover, multiple frameworks exist that allow the reconstruction of 3D ideal-MHD equilibria: V3FIT [17,18], STELLOPT [19], and Minerva [20,21].…”

Section: Jinst 18 P11012mentioning

confidence: 99%

Accelerated Bayesian inference of plasma profiles with self-consistent MHD equilibria at W7-X via neural networks

Merlo,

Pavone,

Böckenhoff

et al. 2023

J. Inst.

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High-β operations require a fast and robust inference of plasma parameters with a self-consistent magnetohydrodynamic (MHD) equilibrium. Precalculated MHD equilibria are usually employed at Wendelstein 7-X (W7-X) due to the high computational cost. To address this, we couple a physics-regularized artificial neural network (NN) model that approximates the ideal-MHD equilibrium with the Bayesian modeling framework Minerva. We show the fast and robust inference of plasma profiles (electron temperature and density) with a self-consistent MHD equilibrium approximated by the NN model. We investigate the robustness of the inference across diverse synthetic W7-X plasma scenarios. The inferred plasma parameters and their uncertainties are compatible with the parameters inferred using the variational moments equilibrium code (VMEC), and the inference time is reduced by more than two orders of magnitude. This work suggests that MHD self-consistent inferences of plasma parameters can be performed between shots.

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Section: Jinst 18 P11012mentioning

confidence: 99%

Accelerated Bayesian inference of plasma profiles with self-consistent MHD equilibria at W7-X via neural networks

Merlo,

Pavone,

Böckenhoff

et al. 2023

J. Inst.

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“…The vacuum rotational transform of CTH plasmas is modified by adjusting the ratio of the currents in the helical and toroidal magnetic field coils. Previous studies involving transform scans in CTH plasmas have demonstrated a range of vacuum rotational transforms from 0.02-0.35 [30]; meanwhile, the range of edge vacuum transform explored with simultaneous CIS measurements include ῑvac = 0.05, 0.06, 0.09 and 0.11. Across all of the vacuum rotational transforms investigated, no significant change -11 - in the ion flow structure was observed.…”

Section: Modification Of He + Ion Flows In Cth Plasmasmentioning

confidence: 99%

Implementation of coherence imaging spectroscopy for ion flow measurements in the Compact Toroidal Hybrid experiment

et al. 2023

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A new coherence imaging spectroscopy (CIS) system has been characterized and validated for measurements of impurity ion velocity in the Compact Toroidal Hybrid (CTH) experiment. CIS is an interferometric technique providing very high spatial resolution of line-integrated ion flows; however, these measurements are highly sensitive to environmental factors such as temperature fluctuations. A compact interferometer design housed in a thermally regulated environment yields CIS measurement variations due to thermal fluctuations of 0.25 km/s. CIS measurements of He+ flows in the outer regions of CTH are benchmarked using two optical grating spectrometers. The deviation between the measurements is typically less than 2 km/s for multiple lines of sight which is well within the uncertainties of the diagnostics. Additional experiments demonstrate a moderate robustness of ion flows in the outer region of CTH to changing the vacuum transform, direction of the magnetic field, and plasma current. In contrast, regions of complete flow reversal are observed when a bias probe is inserted into the plasma edge.

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“…By assuming a closed nested flux surface solution, VMEC computes an equilibrium beyond the axisymmetric limit of the Grad-Shafranov equation. 3D reconstruction codes such as V3FIT [19] and STELLOPT [20] determine the unknown parameters in VMEC from weakly 3D tokamaks [21][22][23], reversed field pinch [24,25] and stellarators [26,27].…”

Section: Introductionmentioning

confidence: 99%

3D equilibrium reconstruction with islands

Cianciosa¹,

Hirshman²,

Seal³

et al. 2018

Plasma Phys. Control. Fusion

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This paper presents the development of a 3D equilibrium reconstruction tool and the results of the first-ever reconstruction of an island equilibrium. The SIESTA non-nested equilibrium solver has been coupled to the V3FIT 3D equilibrium reconstruction code. Computed from a coupled VMEC and SIESTA model, synthetic signals are matched to measured signals by finding an optimal set of equilibrium parameters. By using the normalized pressure in place of normalized flux, non-equilibrium quantities needed by diagnostic signals can be efficiently mapped to the equilibrium. The effectiveness of this tool is demonstrated by reconstructing an island equilibrium of a DIII-D inner wall limited L-mode case with an n=1 error field applied. Flat spots in Thomson and ECE temperature diagnostics show the reconstructed islands have the correct size and phase.

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Non-axisymmetric equilibrium reconstruction of a current-carrying stellarator using external magnetic and soft x-ray inversion radius measurements

Cited by 8 publications

References 23 publications

Accelerated Bayesian inference of plasma profiles with self-consistent MHD equilibria at W7-X via neural networks

Accelerated Bayesian inference of plasma profiles with self-consistent MHD equilibria at W7-X via neural networks

Implementation of coherence imaging spectroscopy for ion flow measurements in the Compact Toroidal Hybrid experiment

3D equilibrium reconstruction with islands

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