Q-Band X-Mode Reflectometry and Density Profile Reconstruction

Qu, Hao; Zhang, Tao; Zhang, Shoubiao; Wen, Fei; Wang, Yumin; Kong, Defeng; Han, Xingwei; Yang, Yilin; Gao, Yu; Huang, Chongxiang; Cai, Jianqing; Gao, Xiang; Team, East

doi:10.1088/1009-0630/17/12/01

Cited by 62 publications

(49 citation statements)

References 21 publications

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“…The electron density was measured by reflectometry (Refl). [27][28][29] The electron temperature was measured by a Michelson interferometer (MI), 30 a heterodyne radiometer system (HRS), 31 and Thomson scattering (TS). 32 The ion temperature was measured by charge exchange recombination spectroscopy (CXRS).…”

Section: Setup Of the Simulationsmentioning

confidence: 99%

Study of power width scaling in scrape-off layer with 2D electrostatic turbulence code based on EAST L-mode discharges

et al. 2019

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Section: Setup Of the Simulationsmentioning

confidence: 99%

Study of power width scaling in scrape-off layer with 2D electrostatic turbulence code based on EAST L-mode discharges

et al. 2019

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“…The probing frequency at which the signal amplitude's gradient suddenly increases can be interpreted as the FF frequency and the start of the upper cut off plasma reflection. This approach has been used in many different devices such as DIII-D [4], Tore Supra [5], EAST [6]. Amplitude based methods require a high dynamic range of the diagnostic measurement and assume that the plasma reflection signal power is consistently higher than other reflections, such as back wall reflection, spurious noise or lower cut off reflection.…”

Section: Automatic Estimation Of the X-mode First Fringe Frequencymentioning

confidence: 99%

Estimation of X-Mode Reflectometry First Fringe Frequency Using Neural Networks

Aguiam

Silva

Guimarãis

et al. 2018

IEEE Trans. Plasma Sci.

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One of the main challenges in X-mode reflectometry is the correct determination of the group delay measurement used for density profile reconstruction. The X-mode upper cut off group delay measurement can be used to reconstruct the electron density profiles from the near zero density. However, due to the broad operational conditions of experimental fusion devices, the start of the upper cut off region can occur at any probing frequency. The first fringe of the interference signal measured by reflectometry, that corresponds to the start of the upper cut off reflection is used together with the magnetic field profile to determine vacuum distance between the reflectometer antenna and the start of the plasma. An incorrect estimation of the first fringe probing frequency not only introduces a radial error but also a group delay error, affecting the shape of the resulting density profile. In this work we present the new developments in the automatic first fringe estimation required for the reliable reconstruction of density profiles, used in the multichannel X-mode density profile reflectometry diagnostic recently installed on ASDEX Upgrade. An improved algorithm to estimate and track the frequency of the first fringe along a discharge is introduced. Tests show that it is able to correctly determine the first fringe for most discharges. However, for a number of unanticipated cases, the algorithm provides jitter and imprecise results, introducing errors in the reconstructed density profiles. We also present a novel neural network approach for the first time for the estimation of the first fringe frequency. A comprehensive training set was carefully selected by experienced reflectometry diagnosticians and used to train the neural network model using the open source software libraries TensorFlow and Keras. The resulting neural network is able to provide more precise first fringe estimations than the previous algorithm. The reconstructed density profiles, using both algorithms, are presented and compared.

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“…where subscript '0' means the value at the magnetic axis, the radial electric field E r can drive the trapped ions to move in the toroidal direction with a velocity v it,ϕ = cE r /B θ [19] . When E r is timedependent, it causes a toroidal acceleration dv it,ϕ /dt = (c/B θ ) • (dE r /dt) which provides an inertia force F in = −m i dv it,ϕ /dt.…”

Section: The Physics Model 21 Neoclassical Polarization Contributionmentioning

confidence: 99%

Effect of Finite-Ion-Banana-Width on the Polarization Contribution to the Neoclassical Tearing Modes Evolution

Hongpeng¹,

Peng²,

Yong³

et al. 2014

Plasma Sci. Technol.

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In the previous analytical description of the neoclassical polarization current effect on the neoclassical tearing modes (NTMs), it is usually assumed that the magnetic island is much larger than the finite-ion-banana-width (FBW). This assumption is questionable when the experimentally observed seed island width of the NTMs is comparable to the FBW. We introduce a simple and direct theoretical method to investigate the FBW effect on the neoclassical polarization contribution to the NTM evolution in collisional plasmas. The results show that, the FBW effect can strongly modify the neoclassical polarization current profile near the island separatrix, and thus weaken its probably stabilizing effect on the NTMs.

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Q-Band X-Mode Reflectometry and Density Profile Reconstruction

Cited by 62 publications

References 21 publications

Study of power width scaling in scrape-off layer with 2D electrostatic turbulence code based on EAST L-mode discharges

Study of power width scaling in scrape-off layer with 2D electrostatic turbulence code based on EAST L-mode discharges

Estimation of X-Mode Reflectometry First Fringe Frequency Using Neural Networks

Effect of Finite-Ion-Banana-Width on the Polarization Contribution to the Neoclassical Tearing Modes Evolution

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