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Beam Ion Losses Caused by Magnetic Field Ripples in Various Plasma Parameter Ranges in the Large Helical Device

Kunihiro OGAWA, Mitsutaka ISOBE¹⁾, Kazuo TOI¹⁾ and LHD Experiment Group¹⁾

Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan

1)

National Institute for Fusion Science, 322-6 Oroshi-cho, Toki 509-5292, Japan

(Received 27 December 2011 / Accepted 2 February 2012 / Published 24 February 2012)

Abstract

Beam ion losses from Large Helical Device (LHD) plasmas caused by magnetic field ripples or Coulomb collisions are measured using a scintillator-based lost fast-ion probe (SLIP). The gyroradius and pitch angle distribution of beam-ion losses as well as to the total-beam losses arriving at the SLIP are measured in various plasma parameter ranges. The SLIP reveals that most lost beam ions consist of a pitch angle of 50°-60° at relatively high toroidal magnetic field strength (B_t). These ions consist of a transition orbit with a large deviation from the flux surface. The beam ion losses arriving at the SLIP (Γ_{SLIP_SUM}) depend on the changes in the line-averaged electron density in a manner analogous to the behavior of beam ion components created by co-going neutral beam injectors. Γ_{SLIP_SUM} normalized by the beam ion components decreases as the magnetic axis position in a vacuum (R_ax) shifts inward at B_t of 0.90 T. Not only beam ions having transition orbit but also those having co-going orbit are measured at the relatively low B_t experiments at R_ax = 3.60 m. The loss domain corresponding to the co-going orbit disappeared at B_t = 0.75 T. Beam ions having transition orbit as well as those having passing orbits normalized by the beam ion components are suppressed with increasing B_t.

Copyright (c) 2012 The Japan Society of Plasma Science and Nuclear Fusion Research

Keywords

beam ion loss, lost fast ion probe, the large helical device

DOI: 10.1585/pfr.7.2402014

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References

• [1] A. Fasoli et al., Nucl. Fusion 47, S264 (2007).
• [2] S.J. Zweben, Nucl. Fusion 29, 825 (1989).
• [3] S. Baeumel et al., Rev. Sci. Instrum. 75, 3563 (2004).
• [4] H. Sanuki et al., Phys. Fluids B 2, 2155 (1990).
• [5] H.E. Minick, Phys. Plasmas 13, 058102 (2006).
• [6] K. Ogawa et al., J. Plasma Fusion Res. SERIES 8, 655 (2009).
• [7] K. Ogawa et al., Nucl. Fusion 50, 084005 (2010).
• [8] M. Yokoyama, J. Plasma Fusion Res. 76, 1176 (2000).
• [9] D.S. Darrow et al., Nucl. Fusion 50, 105009 (2010).

This paper may be cited as follows:

Kunihiro OGAWA, Mitsutaka ISOBE, Kazuo TOI and LHD Experiment Group, Plasma Fusion Res. 7, 2402014 (2012).