Negative-ion-based neutral beam injector for Large Helical Device

Fabrication of a 15 MW, 10 sec. negative-ion-based neutral beam injection system has been started for Large Helical Device (LHD). The system is composed of two beam lines. Each beam line has two ion sources which are designed to deliver 40 A negative hydrogen ions at the beam energy of 180 keV. The beam line has a long gas neutralizer and a magnetic bending system to deal with residual ions. The beam line has also a bending system for accelerated electrons, which we think necessary. Special attention is paid to reduce ferromagnetic materials in the beam line, because helical systems are sensitive to the error magnetic field. The design is based on the results of our R&D on the large negative hydrogen ion source, high density negative hydrogen ion production, high power beam extraction and low beam divergence.