Review of initial experimental results of the PSI studies in the large helical device

The large helical device (LHD) is the largest heliotron type superconducting device. Its operation was started on 31 March 1998. Three experimental campaigns have been completed until the end of 1999. Wall conditioning mainly by cleaning discharges using ECRF or glow discharges worked well even without high temperature baking. The plasma production with ECRH and auxiliary heating with NBI and/or ICRF in the LHD configuration equipped with open helical divertor were well performed. The divertor material was SS316L in the first and second campaigns, and was replaced by the graphite in the third campaign. The influences of the different divertor materials were investigated. Our understanding of the edge and the divertor plasma has progressed. Long-pulse discharges 80 and 68 s heated by NBI (0.5 MW) or ICRF (0.9 MW) have been achieved, respectively. No severe limitation of the duration has appeared.