[Table of Contents]

Plasma and Fusion Research

Volume 3, 041 (2008)

Regular Articles

Gyrokinetic Studies of Ion Temperature Gradient Turbulence and Zonal Flows in Helical Systems
Hideo SUGAMA1,2), Tomo-Hiko WATANABE1,2) and Sergi FERRANDO-MARGALET1)
1)
National Institute for Fusion Science, Toki 509-5292, Japan
2)
Graduate School for Advanced Studies (Sokendai), Toki 509-5292, Japan
(Received 14 April 2008 / Accepted 16 June 2008 / Published 14 July 2008)

Abstract

Gyrokinetic theory and simulation results are presented to investigate regulation of ion temperature gradient (ITG) turbulence due to E × B zonal flows in helical systems. In order to examine effects of changes in helical magnetic configuration on anomalous transport and zonal flows, magnetic field parameters representing the standard and inward-shifted configurations of the Large Helical Device (LHD) [O. Motojima, N. Ohyabu, A. Komori, et al., Nucl. Fusion 43, 1674 (2003)] are used. The linear gyrokinetic analyses show that the largest growth rate of the linear ITG instability for the inward-shifted configuration is slightly higher than that in the standard one while, as theoretically predicted, zonal flows generated by given sources keep larger values for longer time for the inward-shifted case because of a smaller safety factor, a lower aspect ratio, and slower radial drift velocities of helical-ripple-trapped particles. It is shown from the gyrokinetic Vlasov simulation of the ITG turbulence that, in spite of the higher ITG-mode growth rate, the inward-shifted plasma takes a smaller average value of the ion thermal diffusivity in the steady turbulent state with a higher zonal-flow level. These results imply that neoclassical optimization contributes to reduction of the anomalous transport by enhancing the zonal-flow level and give a physical explanation for the confinement improvement observed in the LHD experiments with the inward plasma shift. When equilibrium radial electric fields produce poloidal E × B rotation of helically-trapped particles with reduced radial displacements, further enhancement of zonal flows and resultant transport reduction are theoretically expected.

Keywords

zonal flow, ITG turbulence, gyrokinetic simulation, helical system, LHD

DOI: 10.1585/pfr.3.041

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References

  • [1] P.H. Diamond, S.-I. Itoh, K. Itoh, and T.S. Hahm, Plasma Phys. Control. Fusion 47, R35 (2005).
  • [2] K. Itoh, S.-I. Itoh, P.H. Diamond et al., Phys. Plasmas 13, 055502 (2006).
  • [3] A. Fujisawa, K. Itoh, H. Iguchi et al., Phys. Rev. Lett. 93, 165002 (2004).
  • [4] M. Yokoyama, J. Plasma Fusion Res. 78, 205 (2002).
  • [5] H.E. Mynick, Phys. Plasmas 13, 058102 (2006).
  • [6] D.A. Spong, S.P. Hirshman, L.A. Berry et al., Nucl. Fusion 41, 711 (2001).
  • [7] J.N. Talmadge, V. Sakaguchi, F.S.B. Anderson et al., Phys. Plasmas 9, 5165 (2001).
  • [8] G. Grieger, W. Lotz, P. Merkel et al., Phys. Fluids B 4, 2081 (1992).
  • [9] H. Sugama and T.-H. Watanabe, Phys. Rev. Lett. 94, 115001 (2005).
  • [10] H. Sugama and T.-H. Watanabe, Phys. Plasmas 13, 012501 (2006); H. Sugama and T.-H. Watanabe, ibid. 14, 079902 (2007).
  • [11] T.-H. Watanabe and H. Sugama, 21th IAEA Fusion Energy Conference (Chengdu, China, 2006), EX/5-4.
  • [12] T.-H. Watanabe, H. Sugama and S. Ferrando-Margalet, Nucl. Fusion 47, 1383 (2007).
  • [13] O. Motojima, N. Ohyabu, A. Komori et.al., Nucl. Fusion 43, 1674 (2003).
  • [14] H. Yamada, A Komori, N Ohyabu et al., Plasma Phys. Control. Fusion 43, A55 (2001).
  • [15] T.-H. Watanabe and H. Sugama, Nucl. Fusion 46, 24 (2006).
  • [16] S. Ferrando-Margalet, H. Sugama and T.-H. Watanabe, Phys. Plasmas 14, 122505 (2007).
  • [17] H. Sugama, T.-H. Watanabe, and S. Ferrando-Margalet, Joint Conference of 17th International Toki Conference on Physics of Flows and Turbulence in Plasmas and 16th International Stellarator/Heliotron Workshop 2007 (Toki, Japan, 2007), PI-08.
  • [18] T.-H. Watanabe, H. Sugama, and S. Ferrando-Margalet, Joint Conference of 17th International Toki Conference on Physics of Flows and Turbulence in Plasmas and 16th International Stellarator/Heliotron Workshop 2007 (Toki, Japan, 2007), P2-06.
  • [19] T.-H. Watanabe, H. Sugama and S. Ferrando-Margalet, Phys. Rev. Lett. 100, 195002 (2008).
  • [20] H.E. Mynick and A.H. Boozer, Phys. Plasmas 14, 072507 (2007).
  • [21] K.C. Shaing and S.A. Hokin, Phys. Fluids 26, 2136 (1983).
  • [22] N. Winsor, J.L. Johnson and J.J. Dawson, Phys. Fluids 11, 2248 (1968).
  • [23] M.N. Rosenbluth and F.L. Hinton, Phys. Rev. Lett. 80, 724 (1998).
  • [24] T.S. Hahm, M.A. Beer, Z. Lin, G.W. Hammett, W.W. Lee, and W.M. Tang, Phys. Plasmas 6, 922 (1999).
  • [25] K. Ida et al., Phys. Rev. Lett. 91, 085003 (2003).

This paper may be cited as follows:

Hideo SUGAMA, Tomo-Hiko WATANABE and Sergi FERRANDO-MARGALET, Plasma Fusion Res. 3, 041 (2008).