Strong Nonlocal Effects in a Tokamak Perturbative Transport Experiment

Gentle, K. W.; Rowan, W. L.; Bravenec, R. V.; Cima, Greg; Crowley, T. P.; Gasquet, H.; Hallock, G. A.; Heard, J. W.; Ouroua, A.; Phillips, P. E.; Ross, D. W.; Schoch, P. M.; Watts, Christopher

doi:10.1103/physrevlett.74.3620

Cited by 153 publications

(190 citation statements)

References 6 publications

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“…The ITG-based model with strongest stiffness 16 can reproduce some of the same qualitative characteristics observed in carbon laser blow-off experiments in the Texas Experimental Tokamak ͑TEXT͒. 13 The magnitude and response time of the core T e rise, however, are still in quantitative disagreement with those predicted by the strongest stiff ITG-based model. 15 Moreover, it is an open question whether such models, which take into account two coupled heat diffusion equations ͑for ion and electron͒ with nonlinear thresholds and couplings, can be applied to the thermally decoupled electron-ion regime where the nonlocal T e rise is mainly observed or not.…”

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confidence: 68%

Observation of core electron temperature rise in response to an edge cooling in toroidal helical plasmas

et al. 2005

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The first observation of a significant rise of core electron temperature in response to edge cooling in a helical plasma has been made on the Large Helical Device ͓O. Motojima et al., Phys. Plasmas 6, 1843 ͑1999͔͒. When the phenomenon occurs, the electron heat diffusivity in the core region is reduced abruptly without changing local parameters in the region of interest. Therefore the phenomenon can be regarded as a so-called "nonlocal" electron temperature rise observed so far only in many tokamaks. © 2005 American Institute of Physics. ͓DOI: 10.1063/1.2131047͔The clarification of electron heat transport in magnetically confined plasmas is still an important issue, since the performance of a probable fusion reactor should be determined by electron heating as a result of the interaction between electrons and alpha particles as a fusion reaction product. In order to promote a better understanding of the electron heat transport, the electron heat transport analysis for both transient and steady state has been carried out diligently in many tokamaks 1-3 and helical systems. [4][5][6] One of the significant issues found in these studies is a "nonlocal transport phenomenon" observed in perturbation experiments on many tokamaks 7-12 and a few helical systems. 4 In particular, a rise of the core electron temperature T e invoked by the rapid cooling of the edge plasma has been observed in various tokamaks with both ohmically heated plasmas and plasmas with an auxiliary heating, such as electron cyclotron heating ͑ECH͒, at a sufficiently low density ͑e.g., Ref. 13͒. The amplitude reversal of the cold pulse propagation in the core plasma cannot be explained even by the model based on the assumption that heat flux has a strong nonlinear dependence on temperature and its gradient. In addition there seem to be no changes in the thermodynamic forces, such as those due to the temperature gradient and/or the density gradient, in the core plasma at the onset of the core T e rise. Consequently, the core T e rise invoked by the edge cooling is considered to result from a nonlocality in the electron heat transport. On the contrary, such a core T e rise in response to the edge cooling has not been observed so far in helical systems.14 Recently, to rationalize the so-called "nonlocal" T e rise, some physics-based transport models including a critical gradient scale length, such as the ion temperature gradient ͑ITG͒ model, have been set up and tested.2,15 It should be noted that despite being dependent on local variables, the ITG-based model shows a nonlocal response to small changes in the profiles as a result of a slight deviation from near marginality. The ITG-based model with strongest stiffness 16 can reproduce some of the same qualitative characteristics observed in carbon laser blow-off experiments in the Texas Experimental Tokamak ͑TEXT͒.13 The magnitude and response time of the core T e rise, however, are still in quantitative disagreement with those predicted by the strongest stiff ITG-based model. 15 Moreover, it is an open ...

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confidence: 68%

Observation of core electron temperature rise in response to an edge cooling in toroidal helical plasmas

et al. 2005

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“…[10][11][12][13][14][15][16][17] In cold pulse propagation experiments, for example, the core plasma temperature shows the fast change after the edge cooling. [18][19][20] The change of temperature is much faster than the expected value from the diffusive process in a thermal transport. It is considered that some linkages between edge and core.…”

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confidence: 99%

Observation of multi-scale turbulence and non-local transport in LHD plasmas

et al. 2014

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We have studied two types of spatio-temporal turbulence dynamics in plasmas in the Large Helical Device, based on turbulence measurements with high spatial and temporal resolution. Applying conditional ensemble-averaging to a plasma with Edge-Localized Modes (ELMs), fast radial inward propagation of a micro-scale turbulence front is observed just after ELM event, and the propagation speed is evaluated as ∼100 m/s. A self-organized radial electric field structure is observed in an electrode biasing experiment, and it is found to realize a multi-valued state. The curvature of the radial electric field is found to play an important role for turbulence reduction.

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“…Another important consequence that the nonlinear flux can induce is the dynamic response of the core flows against the edge perturbation [23][24][25][26][27][28]. As discussed above, the nonlinear flux allows the fluctuation momentum to propagate faster than the mean momentum.…”

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confidence: 99%

“…This effect is a key for understanding why "the tail wags the plasma," i.e., why jogging edge flows by changing magnetic geometry leaves a footprint in the core flow. A perturbative experiment [23][24][25][26][27][28] is proposed as a further critical test.…”

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How turbulence fronts induce plasma spin-up

et al. 2017

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A calculation which describes the spin-up of toroidal plasmas by the radial propagation of turbulence fronts with broken parallel symmetry is presented. The associated flux of parallel momentum is calculated by using a two-scale direct-interaction approximation in the weak turbulence limit. We show that fluctuation momentum spreads faster than mean flow momentum. Specifically, the turbulent flux of wave momentum is stronger than the momentum pinch. The scattering of fluctuation momentum can induce edge-core coupling of toroidal flows, as observed in experiments.

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Strong Nonlocal Effects in a Tokamak Perturbative Transport Experiment

Cited by 153 publications

References 6 publications

Observation of core electron temperature rise in response to an edge cooling in toroidal helical plasmas

Observation of core electron temperature rise in response to an edge cooling in toroidal helical plasmas

Observation of multi-scale turbulence and non-local transport in LHD plasmas

How turbulence fronts induce plasma spin-up

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