[Table of Contents]

Plasma and Fusion Research

Volume 7, 1402028 (2012)

Regular Articles

Characterization of Quasi-Single-Helicity States in a Low-Aspect-Ratio RFP
Kensuke OKI, Daisuke FUKAHORI, Kazuaki DEGUCHI, Seiya NAKAKI, Akio SANPEI, Haruhiko HIMURA, Sadao MASAMUNE and Roberto PACCAGNELLA1)
Kyoto Institute of Technology, Kyoto 606-8585, Japan
1)
Consorzio RFX and Istituto Gas Ionizzati del C.N.R, Padova, 35127, Italy
(Received 5 January 2012 / Accepted 26 February 2012 / Published 15 April 2012)

Abstract

Characteristics of quasi-single-helicity (QSH) states have been studied in a low-aspect-ratio reversed field pinch (RFP) machine RELAX mainly by magnetic diagnostics. Internal profiles of the fluctuating radial, poloidal and toroidal magnetic fields have shown good agreement with eigenfunctions of a single helical mode. The edge magnetic fluctuation spectra are somewhat broader than what are expected from internal magnetic field profiles. In spite of these slight discrepancies, the usual measure for the QSH, the spectral index NS lower than 2, still provides a reasonable measure for QSH states in RELAX. The QSH persistence has been improved in RELAX by the reduction of the poloidal resistance of flanges at poloidal gaps, mainly due to the improved axisymmetry of the toroidal magnetic field. QSH persistence more than 30% of the flat-topped current phase has been realized with current density lower than in other RFP, and probability of spontaneous QSH is 12.8 ± 7.3% which is higher than high-aspect-ratio RFP. It suggests the advantage of low-aspect-ratio configuration in attaining to the QSH. Comparison with recent experiments using active resonant perturbation may suggest the importance of further reduction of field errors to improve the quality of QSH.

Keywords

quasi-single-helicity (QSH), reversed field pinch, low aspect ratio RFP, magnetic fluctuation, internal magnetic field

DOI: 10.1585/pfr.7.1402028

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References

  • [1] P. Martin et al., Nucl. Fusion 43, 1855 (2003).
  • [2] R. Lorenzini et al., Nature Physics 5, 570 (2009).
  • [3] D.F. Escande et al., Phys. Rev. Lett. 85, 3169 (2000).
  • [4] H. Sugimoto et al., Plasma Phys. Control. Fusion 47, 1287 (2005).
  • [5] T. Onchi et al., Plasma Fusion Res. 3, 005 (2008).
  • [6] T. Onchi et al., Rev. Sci. Instrum. 81, 073502 (2010).
  • [7] T. Onchi et al., J. Phys. Soc. Jpn. 80, 114501 (2011).
  • [8] A. Sanpei et al., Plasma Fusion Res. 6, 2406096 (2011).
  • [9] S. Masamune et al., J. Phys. Soc. Jpn. 76, 123501 (2007).
  • [10] A. Sanpei et al., J. Plasma Fusion Res. SERIES 8, 1066 (2009).
  • [11] A. Sanpei et al., J. Phys. Soc. Jpn. 78, 013501 (2009).
  • [12] R. Ikezoe et al., Plasma Phys. Control. Fusion 53, 025003 (2011).
  • [13] R. Ikezoe et al., Plasma Fusion Res. 3, 029 (2008).
  • [14] K. Oki et al., J. Phys. Soc. Jpn. 77, 075005 (2008).
  • [15] J.M. Finn et al., Phys. Fluids B 4, 1262 (1992).
  • [16] R. Paccagnella, presentation at the IEA/RFP Workshop in Madison (2000).
  • [17] L. Frassinetti et al., Phys. Plasmas 14, 112510 (2007).
  • [18] D. Bonfiglio et al., Nucl. Fusion 51, 063016 (2011).
  • [19] L. Frassinetti et al., Nucl. Fusion 50, 035005 (2010).

This paper may be cited as follows:

Kensuke OKI, Daisuke FUKAHORI, Kazuaki DEGUCHI, Seiya NAKAKI, Akio SANPEI, Haruhiko HIMURA, Sadao MASAMUNE and Roberto PACCAGNELLA, Plasma Fusion Res. 7, 1402028 (2012).