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(CT-6Rb) Engineering Prospects of Negative-ion-based Neutral Beam Injection System from High Power Operation for the Large Helical Device

O. Kaneko¹⁾, Y. Takeiri¹⁾, K. Tsumori¹⁾, Y. Oka¹⁾, M. Osakabe¹⁾, K. Ikeda¹⁾, K. Nagaoka¹⁾, T. Kawamoto¹⁾, E. Asano¹⁾, M. Sato^1)
 
1) National Institute for Fusion Science, Toki, Japan

Abstract.  An overview on four-year operation of the negative-ion-based NBI (N-NBI) system for LHD is presented, and the prospects of negative-ion technology for applying it to helical fusion reactors are discussed from theses experiences. The N-NBI system was designed and constructed based on the results of R&D in NIFS. Using three beam lines, the total port-through injection power of 9 MW for 2 s has been achieved. Each beam line attained the same performance: 3.5 MW of the injection power with the beam energy of 165 keV for hydrogen, which corresponds to the averaged negative ion current density of 25mA/cm² from ion sources. Also for long pulse injections, 110 s for 0.1 MW by one ion source, and 80 s for 0.5 MW by two ion sources (one beam line) were carried out. These facts show that the negative ion technology has been established to the same power level of positive ion system. Several technical improvements needed for these successful results are described, and the problems that limit the present performance are clarified. Solutions to these problems are discussed and some R&D programs are proposed for further improvement.

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