A theory of self-organized zonal flow with fine radial structure in tokamak

Journal Article · Tue Dec 12 00:00:00 EST 2017 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.4995302· OSTI ID:1523374

Zhang, Y. Z. ^[1]; Liu, Z. Y. ^[2]; Xie, T. ^[3]; Mahajan, S. M. ^[4]; Liu, J. ^[5]

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1. Chinese Academy of Sciences (CAS), Hefei (China). Center for Magnetic Fusion Theory; none
2. Univ. of Science and Technology of China, Hefei (China). Dept. of Modern Physics
3. Sichuan Univ. of Science and Engineering, Zigong (China). School of Science
4. Univ. of Texas, Austin, TX (United States). Inst. for Fusion Studies
5. Chinese Academy of Sciences (CAS), Hefei (China). Center for Magnetic Fusion Theory; Univ. of Science and Technology of China, Hefei (China). Dept. of Modern Physics

The (low frequency) zonal flow-ion temperature gradient (ITG) wave system, constructed on Braginskii's fluid model in tokamak, is shown here to be a reaction-diffusion-advection system; it is derived by making use of a multiple spatiotemporal scale technique and two-dimensional (2D) ballooning theory. For real regular group velocities of ITG waves, two distinct temporal processes, sharing a very similar meso-scale radial structure, are identified in the nonlinear self-organized stage. The stationary and quasi-stationary structures reflect a particular feature of the poloidal group velocity. The equation set posed to be an initial value problem is numerically solved for JET low mode parameters; the results are presented in several figures and two movies that show the spatiotemporal evolutions as well as the spectrum analysis—frequency-wave number spectrum, auto power spectrum, and Lissajous diagram. This approach reveals that the zonal flow in tokamak is a local traveling wave. For the quasi-stationary process, the cycle of ITG wave energy is composed of two consecutive phases in distinct spatiotemporal structures: a pair of Cavitons growing and breathing slowly without long range propagation, followed by a sudden decay into many Instantons that carry negative wave energy rapidly into infinity. A spotlight onto the motion of Instantons for a given radial position reproduces a Blob-Hole temporal structure; the occurrence as well as the rapid decay of Caviton into Instantons is triggered by zero-crossing of radial group velocity. A sample of the radial profile of zonal flow contributed from 31 nonlinearly coupled rational surfaces near plasma edge is found to be very similar to that observed in the JET Ohmic phase [J. C. Hillesheim et al., Phys. Rev. Lett. 116, 165002 (2016)]. The theory predicts an interior asymmetric dipole structure associated with the zonal flow that is driven by the gradients of ITG turbulence intensity.

• Research Organization: Chinese Academy of Sciences (CAS), Hefei (China); Sichuan Univ. of Science and Engineering, Zigong (China); Univ. of Science and Technology of China, Hefei (China); Univ. of Texas, Austin, TX (United States)
• Sponsoring Organization: Foundation of Sichuan Univ. of Science and Engineering (China); Key Research Program of Frontier Sciences CAS (China); National Magnetic Confinement Fusion Energy Research Project (China); National Natural Science Foundation of China (NSFC); Scientific Research Fund of the Sichuan Provincial Education Dept. (China); USDOE; USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24)
• Grant/Contract Number: FG02-04ER54742
• OSTI ID: 1523374
• Alternate ID(s): OSTI ID: 1413020
• Journal Information: Physics of Plasmas, Journal Name: Physics of Plasmas Journal Issue: 12 Vol. 24; ISSN 1070-664X
• Publisher: American Institute of Physics (AIP)
• Country of Publication: United States
• Language: English

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70 PLASMA PHYSICS AND FUSION TECHNOLOGY