26aA01
流体的旋回度を伴うドリフト波乱流による平行運動量輸送
Parallel momentum transport by drift wave turbulence with hydrodynamic
helicity
小菅佑輔1,2、伊藤早苗2,3、P.H. Diamond4、伊藤公孝3,5
Y. Kosuga1,2, S.-I. Itoh2,3, P.H. Diamond4, K. Itoh3,51

九州大学高等研究院、2九州大学応用力学研究所、3九州大学極限プラズマ研究連携センタ
ー、4UCSD、5核融合科学研究所
1Institute for Advanced Study, Kyushu Univ., 2Research Institute for Applied Mechanics, Kyusyu
Univ., 3Research Center for Plasma Turbulence, Kyushu Univ., 4UCSD, 5National Institute forFusion ScienceFlows along the magnetic field are ubiquitous innature and laboratory plasmas. In particular, parallel
flows play important role in magnetic fusion, bystabilizing harmful MHD and/or regulatingtransport. Recent experiments report generation ofintrinsic flows, which are likely to be linked tomomentum transport by turbulent fluctuation[1].
More recently, the reversal of parallel flows isreported from basic experiments[2]. In theseexperiments, simultaneous measurements ofparallel flow profile and momentum flux clearly
indicate the role of turbulent momentum transport
to cause the flow reversal.
In order to understand its generation mechanism,
several theory has been developed to model parallel
momentum transport. One mechanism forgenerating parallel flows is via a residual stress - acomponent of the momentum flux that remains
finite as parallel flow shear and parallel flow goesto zero[3]. It is formulated that the residual stressarises as a consequence of parallel momentum
transport by drift wave turbulence.
In this work, we discuss the relation of parallel
momentum of waves and helicity of the underlying
fluctuation. Here we define the helicity for drift
wave turbulence byℎ = 𝑞𝑣! ,(1)with 𝑞 = (𝑛! /𝑛! ) − 𝜌!! ∇!! (𝑒𝜑/𝑇! ). Note that thehelicity and the wave momentum is related with
one another, sinceℎ~𝑘! 1 + 𝜌!! 𝑘!! |𝜑! |! /𝜔! ~𝑘! 𝑁! ,(2)where 𝑁! is the action density of drift waves. The
evolution of the helicity is calculated by using theHasegawa-Wakatani equation with parallel flow
coupling[4] and is given by

𝜕! 𝑞𝑣! + 𝜕! 𝑣! 𝑞𝑣! = − 𝑣! 𝑞 𝑣! ! − 𝑣! 𝑣! 𝑞 ! −!∇ !
𝑐!! ! ! − 𝑞∇! 𝑣! .
(3)!!

Here we followed the standard notation. Based on
the helicity balance, the role of spreading offluctuation helicity (the second term in the lefthandside) in driving parallel momentum transport isdiscussed. The parallel momentum transport via thespreading of fluctuation helicity is complementary
to the parallel momentum transport by drift waves.
The former corresponds to the parallel momentum
transport by the nonlinear radial propagation ofturbulence, while the latter corresponds to that bywave propagation. The calculation of the flux offluctuation helicity is on-going, by using thetwo-scale direct interaction approximation[5].
We acknowledge Prof. Inagaki, Dr. Kobayashi,
Dr. Z. Guo, Dr. L. Wang, and the participants in theFestival de Theorie for stimulating discussion andencouragement. This work was partly supported by
the Grants-in-Aid for Scientific Research of JSPSof Japan (23244113, 15K17799, 15H02155), AsadaScienceFoundation,Kyushu
University
Interdisciplinary Programs in Education andProjects in Research Development (26705).
[1] K. Ida and J.E. Rice, Nucl. Fusion 54 045001(2014)[2] S. Inagaki, et al. submitted to Sci. Rep. (2015)[3] P.H. Diamond, et al. Phys. Plasmas 15 012303(2008)[4] Y. Kosuga, S.-I. Itoh, and K. Itoh, submitted toContrib. Plasma Phys. (2015)[5] Lu Wang, Tiliang Wen, and P.H. Diamond,Phys. Plasmas 22 052303 (2015)