[Table of Contents]

Plasma and Fusion Research

Volume 7, 2402014 (2012)

Regular Articles

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
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)


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 (Bt). These ions consist of a transition orbit with a large deviation from the flux surface. The beam ion losses arriving at the SLIP (ΓSLIP_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. ΓSLIP_SUM normalized by the beam ion components decreases as the magnetic axis position in a vacuum (Rax) shifts inward at Bt of 0.90 T. Not only beam ions having transition orbit but also those having co-going orbit are measured at the relatively low Bt experiments at Rax = 3.60 m. The loss domain corresponding to the co-going orbit disappeared at Bt = 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 Bt.


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

DOI: 10.1585/pfr.7.2402014


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This paper may be cited as follows:

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