Advanced divertor scenario in the large helical device

The modification of the open helical divertor (HD) to the closed HD in the Large Helical Device (LHD) heliotron has been investigated using fully three-dimensional neutral transport code EIRENE, to accomplish the active particle control to improve plasma confinement and to sustain high performance long pulse discharges. For the first step to the full closed HD, the torus-inboard side divertor is planned to be modified first in the LHD. The exploring of the structure has been conducted using EIRENE code by trial and error. The code was examined in advance by comparing to spectroscopic observations, and the results of calculation agreed well with the observations. Results of the exploring show that proper rearrangement of divertor plates and additional components, such as dome structure make the neutral particles to be compressed in the divertor region, and effective divertor pumping to be possible. Based on the simulation and experimental results, design and installation of closed HD is programmed in LHD. (author)