Dynamical programming based turbulence velocimetry for fast visible imaging of tokamak plasma

Banerjee, Santanu; Zushi, H.; Nishino, Norikazu; Mishra, K.; Onchi, Takumi; Kuzmin, A.; Nagashima, Yoshihiko; Hanada, K.; Nakamura, K.; Idei, H.; Hasegawa, Makoto; Fujisawa, A.

doi:10.1063/1.4914838

Cited by 11 publications

(8 citation statements)

References 19 publications

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“…[165][166][167] Poloidal rotation is observed in GPI in either in the electron or ion diamagnetic direction, as discussed in Sec. II C. Although there are several difficulties and subtleties in this velocimetry analysis, the observed velocities are near the expected poloidal E rad × B and/or diamagnetic drift speeds of V pol ≤ 10 km/s, i.e., far below the ion sound speed.…”

Section: G Plasma Rotation and Radial Transport From Gpimentioning

confidence: 73%

Invited Review Article: Gas puff imaging diagnostics of edge plasma turbulence in magnetic fusion devices

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Terry

Stotler

et al. 2017

Review of Scientific Instruments

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Gas puff imaging (GPI) is a diagnostic of plasma turbulence which uses a puff of neutral gas at the plasma edge to increase the local visible light emission for improved space-time resolution of plasma fluctuations. This paper reviews gas puff imaging diagnostics of edge plasma turbulence in magnetic fusion research, with a focus on the instrumentation, diagnostic cross-checks, and interpretation issues. The gas puff imaging hardware, optics, and detectors are described for about 10 GPI systems implemented over the past ∼15 years. Comparison of GPI results with other edge turbulence diagnostic results is described, and many common features are observed. Several issues in the interpretation of GPI measurements are discussed, and potential improvements in hardware and modeling are suggested.

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Section: G Plasma Rotation and Radial Transport From Gpimentioning

confidence: 73%

Invited Review Article: Gas puff imaging diagnostics of edge plasma turbulence in magnetic fusion devices

Zweben

Terry

Stotler

et al. 2017

Review of Scientific Instruments

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“…To extract the time varying 2D velocity field θ r t v , , ( ) from the intensity fluctuations recorded with the GPI diagnostic, we use the orthogonal dynamic programming (ODP) technique. The ODP technique is described in detail in [24] and the salient features are only discussed briefly here. ODP is a robust technique for searching optical alignments of patterns through the simple realization of cross correlation.…”

Section: Application Of Velocimetry To Gpimentioning

confidence: 99%

Energy exchange dynamics across L–H transitions in NSTX

et al. 2017

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We studied the energy exchange dynamics across the low-to-high-confinement (L-H) transition in NSTX discharges using the gas-puff imaging (GPI) diagnostic. The investigation focused on the energy exchange between flows and turbulence to help clarify the mechanism of the L-H transition. We applied this study to three types of heating schemes, including a total of 17 shots from the NSTX 2010 campaign run. Results show that the edge fluctuation characteristics (fluctuation levels, radial and poloidal correlation lengths) measured using GPI do not vary just prior to the H-mode transition, but change after the transition. Using a velocimetry approach (orthogonal-dynamics programming), velocity fields of a × 24 30 cm GPI view during the L-H transition were obtained with good spatial (∼1 cm) and temporal (∼2.5 μs) resolutions. Analysis using these velocity fields shows that the production term is systematically negative just prior to the L-H transition, indicating a transfer from mean flows to turbulence, which is inconsistent with the predator-prey paradigm. Moreover, the inferred absolute value of the production term is two orders of magnitude too small to explain the observed rapid L-H transition. These discrepancies are further reinforced by consideration of the ratio between the kinetic energy in the mean flow to the thermal free energy, which is estimated to be much less than 1, suggesting again that the turbulence depletion mechanism may not play an important role in the transition to the H-mode. Although the Reynolds work therefore appears to be too small to directly deplete the turbulent free energy reservoir, order-of-magnitude analysis shows that the Reynolds stress may still make a non-negligible contribution to the observed poloidal flows.

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“…'Hot' colormap has been used where white color indicates the highest density and black color indicates the lowest density. The images have been superposed on quiver plots of the radial and poloidal velocities of the plasma obtained from velocimetry measurements [21,22]. It is to be noted that the visible images acquired by GPI are taken here as a proxy of the density contours as the intensity is mainly proportional to the density, and its T e dependence has been neglected.…”

Section: Results From Nstx Datamentioning

confidence: 99%

Experimental validation of universal plasma blob formation mechanism

et al. 2022

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Anomalous plasma transport in the boundary region of a tokamak plasma is commonly associated with the formation and evolution of coherent density structures known as blobs. Recently, a theory for a universal mechanism of plasma blob formation has been put forward. It is based on a breaking process of a radially elongated streamer due to poloidal and radial velocity shears. The theory is well supported by two-dimensional and three-dimensional numerical simulation results but lacks experimental validation. In this work, we report the first ever experimental validation of this universal criterion by testing it against NSTX data on blobs obtained using the gas-puff imaging (GPI) diagnostic. It is found that the criterion is widely satisfied in most L-mode discharges and may explain the significantly larger number of blob events. We also validate the theoretical criterion against ADITYA Langmuir probe data taken in the scrape-off layer region.

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Dynamical programming based turbulence velocimetry for fast visible imaging of tokamak plasma

Cited by 11 publications

References 19 publications

Invited Review Article: Gas puff imaging diagnostics of edge plasma turbulence in magnetic fusion devices

Invited Review Article: Gas puff imaging diagnostics of edge plasma turbulence in magnetic fusion devices

Energy exchange dynamics across L–H transitions in NSTX

Experimental validation of universal plasma blob formation mechanism

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