Optimized tomography methods for plasma emissivity reconstruction at the ASDEX Upgrade tokamak

Odstrčil, T.; Pütterich, T.; Odstrčil, Michal; Gude, A.; Igochine, V.; Stroth, U.

doi:10.1063/1.4971367

Cited by 43 publications

(35 citation statements)

References 52 publications

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“…The density of argon was inferred from the soft X-ray radiation. In the upper right box, the soft X-ray (SXR) emissivity profile from tomographic inversion of the measured radiances [18] is shown as a grey band which reflects the assumed relative uncertainty of 10%. The soft X-ray cameras have a 75 µm thick Be-filter in front of the silicon diodes.…”

Section: Application To An H-mode Plasma With Strong Argon Radiationmentioning

confidence: 99%

Influence of CX-reactions on the radiation in the pedestal region at ASDEX Upgrade

et al. 2020

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The radial density profiles of Ne 10+ and Ne 8+ have been measured with charge exchange recombination spectroscopy in an H-mode discharge in ASDEX Upgrade. When trying to fit the data with an impurity transport code that only takes electronic ionisation and recombination into account, the density of Ne 8+ is too low by more than an order of magnitude indicating that an additional recombination mechanism must be at work. We ascribe the missing recombination channel to charge exchange (CX) reactions between neutral deuterium and the impurity ions, which has long been known to be a very efficient recombination reaction. Including the CXreactions yields a good fit of the ionisation balance and delivers the neutral density profile in the pedestal, which is not known from other diagnostics. Here, the CXreactions lead to a change of the ionisation balance on the whole flux surface and the measurement delivers a flux surface averaged neutral density with the exception of the region very close to the X-point. Furthermore, it leads to an increase of the pedestal radiation of neon since the partially ionised stages can emit line radiation. This amounts to an increase of the radiated power of neon inside of the separatrix by a factor of 5. A similar analysis was done for argon in an H-mode discharge dominated by Ar radiation. Only the CX-recombination in the pedestal can explain the radiated power inside the separatrix, which would be too low by a factor of 2.2 without CX. In addition, the radiances of VUV lines from many charge stages are much better fitted when including the CX-recombination. A simple projection of the impact of CX-recombination to the much hotter ITER pedestals shows that for elements up to Kr, a beneficial increase of edge radiated power per core radiated power and of radiated power per central dilution is obtained, while for Xe and especially for W the effect is weak.

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Section: Application To An H-mode Plasma With Strong Argon Radiationmentioning

confidence: 99%

Influence of CX-reactions on the radiation in the pedestal region at ASDEX Upgrade

et al. 2020

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“…This diagnostic provides eight pinhole cameras arranged in a poloidal plane of the plasma with a total of 208 lines of sight (LOS). A novel fast tomography code [44] was developed for the inversion of the measured line-integrated brightness, that provides high accuracy and resolution necessary for the investigation of the asymmetries and the impurity transport.…”

Section: Study Of the Poloidal Asymmetry In Nbi Heated Dischargesmentioning

confidence: 99%

“…Due to the very steep tungsten SXR radiation profiles, the multiplication factor before ∆ R can reach values up to 20 m −1 . A sufficiently good accuracy is achieved using a self-consistent calibration and alignment of the diagnostic, as is described in [44]. It was applied to reduce systematical uncertainties in the geometry of the diagnostic, which significantly reduced reconstruction accuracy.…”

Section: Study Of the Poloidal Asymmetry In Nbi Heated Dischargesmentioning

confidence: 99%

The physics of W transport illuminated by recent progress in W density diagnostics at ASDEX Upgrade

Odstrčil

Pütterich

Angioni

et al. 2017

Plasma Phys. Control. Fusion

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Due to the high mass and charge of the heavy ions, centrifugal and electrostatic forces cause a significant variation in their poloidal density. The impact of these forces on the poloidal density profile of tungsten was investigated utilizing the detailed two-dimensional SXR emissivity profiles from the ASDEX Upgrade tokamak. The perturbation in the electrostatic potential generated by magnetic trapping of the non-thermal ions from neutral beam injection was found to be responsible for significant changes in the poloidal distribution of tungsten ions. An excellent match with the results from fast particle modeling was obtained, validating the model for the poloidal fast particle distribution. Additionally, an enhancement of the neoclassical transport due to an outboard side impurity localization was measured in the experiment when analyzing the tungsten flux between sawtooth crashes. A qualitative match with neoclassical modeling was found, demonstrating the possibility of minimizing neoclassical transport by an optimization of the poloidal asymmetry profile of the impurity.

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“…Reconstruction techniques operating with the Fourier transform and matrix inversion methods [18][19][20][21][22][23][24], face difficulties. For such underdetermined systems, regularisation or iterative fitting methods can be used [25,26]. For our purpose, we have employed the iterative algorithm of maximum likelihood with mathematical expectation maximisation (ML-EM) [21,22,27,28].…”

Section: Methods Of Tomographic Reconstructionmentioning

confidence: 99%

Optical tomography diagnostic for study of neutral plasma component in the gas dynamic trap

Lizunov,

Khilchenko,

Moiseev

et al. 2021

Preprint

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The optical diagnostic observing D-𝛼 line emission along multiple chords in the boundary region close to the plasma absorber, is recently installed at the gas dynamic trap. The implemented pattern of viewing lines is suitable for a tomographic reconstruction of local emissivity profiles, although steps towards increasing the channel count and extending of angular plasma coverage must be taken. The optical registration system of a modular design uses avalanche photodiodes with wideband amplifiers for a large signal dynamic range and the effective time resolution of 1𝜇𝑠. The iterative backward projection technique based on the maximum likelihood principle, demonstrates an acceptable computation accuracy. Images of plasma evolution in the cross section were obtained. Tools for the correlation analysis were also developed and first results of study of the plasma turbulence are presented.

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Optimized tomography methods for plasma emissivity reconstruction at the ASDEX Upgrade tokamak

Cited by 43 publications

References 52 publications

Influence of CX-reactions on the radiation in the pedestal region at ASDEX Upgrade

Influence of CX-reactions on the radiation in the pedestal region at ASDEX Upgrade

The physics of W transport illuminated by recent progress in W density diagnostics at ASDEX Upgrade

Optical tomography diagnostic for study of neutral plasma component in the gas dynamic trap

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