Turbulence elasticity: a key concept to a unified paradigm of L → I → H transition. (April 2015)

• Record Type: Journal Article
• Authors: Guo, Z.B.; Diamond, P.H.; Kosuga, Y.; Gürcan, Ö.D.
• Is Part Of: Nuclear fusion. Volume 55:Number 4(2015:Apr.)
• Page Start: R35
• Page End: 983
• Publication Date: 2015-04
• Subjects: Nuclear fusion -- Periodicals; 621.48405
• DOI: 10.1088/0029-5515/55/4/043022
• Languages: English
• ISSNs: 0029-5515

Abstract

<abstract> <title>Abstract</title> <p>We present a theory of turbulence elasticity, which follows from delayed response of drift waves (DWs) to zonal flow (ZF) shears. It is shown that when |〈<italic>V</italic>〉′<sub>ZF</sub>|/Δ<italic>ω</italic><sub><italic>k</italic></sub> ⩾ 1, with |〈<italic>V</italic>〉′<sub>ZF</sub>| the ZF shearing rate and Δ<italic>ω</italic><sub><italic>k</italic></sub> the local turbulence decorrelation rate, the ZF evolution equation is converted from a diffusion equation to a telegraph equation. This insight provides a natural framework for understanding temporally periodic ZF structures, e.g., propagation of the ZF/turbulence intensity fronts. Furthermore, by incorporating the elastic property of the DW–ZF turbulence, we propose a unified paradigm of low-confinement-mode to intermediate-confinement-mode to high-confinement-mode (L → <italic>I</italic> → <italic>H</italic>) transitions. In particular, we predict the onset and termination conditions of the limit cycle oscillations, i.e. the I-mode. The transition from an unstable L-mode to I-mode is predicted to occur when Δ<italic>ω</italic><sub><italic>k</italic></sub> < |〈<italic>V</italic>〉′<sub>ZF</sub>|<〈<italic>V</italic>〉′<sub>cr</sub>, where 〈<italic>V</italic>〉′<sub>cr</sub> is a critical flow shearing rate and is derived explicitly. If |〈<italic>V</italic>〉′<sub><italic>E</italic>×<italic>B</italic></sub>| > 〈<italic>V</italic>〉′<sub>cr</sub>(〈<italic>V</italic>〉<sub><italic>E</italic>×<italic>B</italic></sub> is mean <italic>E</italic> × <italic>B</italic> shear flow driven by edge radial electrostatic field), the I-mode will terminate and spiral into the H-mode.</p> </abstract>