2018 Volume 13 Pages 3402031
Response of plasmas in Large Helical Device (LHD) to the tungsten pellet injection depends on both the total port-through power of the neutral beam injection (NBI) for heating, PNBI, and the line-averaged electron density, ne. The plasma can be sustained in the range of high PNBI and low ne while it collapses in the range of low PNBI and high ne. When the number of tungsten atoms enclosed in a pellet, NW, is small, plasma can survive in low PNBI and high ne range. Parameter space for plasma sustainment after the pellet injection is limited to lower ne range in more outward-shifted magnetic configuration. ne < 4.0 × 1013 cm−3 and NW < 1.2 × 1018 for Rax = 3.60 m, ne < 3.0 × 1013 cm−3 and NW < 8.7 × 1016 for Rax = 3.75 m, and ne < 2.0 × 1013 cm−3 and NW < 3.1 × 1016 for Rax = 3.90 m are appropriate parameter ranges for the plasma sustainment. This suggests that robustness against tungsten injection depends on the magnetic configurations.