2012 Volume 7 Pages 2402014
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.