Regular Articles

Full Text / References

Density Dependence of Low-Frequency Edge Harmonic Oscillations in LHD H-Mode Plasmas

Wenqing HU¹⁾, Tatsuya KOBAYASHI^1,2,3), Tokihiko TOKUZAWA^1,2,3)

1)

The Graduate University for Advanced Studies, SOKENDAI, Toki 509-5292, Japan

2)

National Institute for Fusion Science, National Institutes of Natural Sciences, Toki 509-5292, Japan

3)

Research Institute for Applied Mechanics, Kyushu University, Kasuga 816-8580, Japan

(Received 6 April 2025 / Accepted 25 June 2025 / Published 17 October 2025)

Abstract

This paper investigates the density dependence of low-frequency edge harmonic oscillations (LF-EHOs) in the Large Helical Device (LHD) H-mode plasmas. A series of discharges with varying density settings reveal that the L-H mode transition occurs above a certain density threshold, and LF-EHOs appear only above an even higher density threshold. In discharges exhibiting LF-EHOs, the cross-coherence between density and magnetic fluctuations for the fundamental frequency remains consistently high across the entire density range. In contrast, the cross-coherence for the second harmonic exhibits an increasing trend with higher plasma density. These findings suggest that the LF-EHO potentially plays a noticeable role in edge profile saturation.

Copyright (c) 2025 The Japan Society of Plasma Science and Nuclear Fusion Research

Keywords

LHD, H-mode, MHD fluctuation, L-H mode transition, beam emission spectroscopy (BES)

DOI: 10.1585/pfr.20.1402044

Full Text

PDF format (2.3Mbytes)

References

• [1] F. Wagner et al., Phys. Rev. Lett. 49, 1408 (1982).
• [2] W. Suttrop et al., Plasma Phys. Control. Fusion 46, A151 (2004).
• [3] K.H. Burrell et al., Phys. Plasmas 23, 056103 (2016).
• [4] F. Wagner, Plasma Phys. Control. Fusion 49, B1 (2007).
• [5] T. Estrada et al., Contrib. Plasma Phys. 50, 501 (2010).
• [6] M. Hirsch et al., Plasma Phys. Control. Fusion 50, 053001 (2008).
• [7] K. McCormick et al., Phys. Rev. Lett. 89, 1 (2002).
• [8] K. Toi et al., Fusion Sci. Technol. 58, 61 (2010).
• [9] M. Ono et al., Plasma Fusion Res. 11, 1402115 (2016).
• [10] W. Hu et al., Plasma Fusion Res. 16, 2402031 (2021).
• [11] T. Oishi et al., Nucl. Fusion 46, 317 (2006).
• [12] S. Kado et al., J. Nucl. Mater. 363-365, 522 (2007), Plasma-Surface Interactions-17.
• [13] T. Oishi et al., Plasma Fusion Res. 3, S1010 (2008).
• [14] H. Takahashi et al., Nucl. Fusion 57, 086029 (2017).
• [15] T. Kobayashi et al., Plasma Phys. Control. Fusion 62, 13 (2020).
• [16] S. Sakakibara et al., Fusion Sci. Technol. 58, 471 (2010).
• [17] K.H. Burrell et al., Phys. Plasmas 8, 2153 (2001).
• [18] W. Hu et al., J. Phys. Soc. Jpn. 94, 064501 (2025), https://doi.org/10.7566/JPSJ.94.064501.
• [19] LHD experiment data repository, https://doi.org/10.57451/lhd.analyzed-data.