LHD diagnostics towards steady state operation

Summary form only given, as follows. The Large Helical Device, LHD, is the world largest helical system having all superconducting coils. After completion of LHD in 1998, 6 experimental campaigns have been carried out successfully. The maximum stored energy, electron temperature, and beta value are 1.2 MJ, 10 keV, 3.2 %, respectively. The confinement time of the LHD plasma appears to be equivalent to that, of tokamaks. One of the most important missions for LHD is to prove steady state operation, which is also significant to ITER and to future fusion reactors. LHD is quite appropriate for this purpose based upon the beneficial feature of a helical system, that is, no necessity of the plasma current. So far, the plasma discharge duration was achieved up to 127 sec. The plasma density was kept constant by feedback control of gas puffing with real time information of the line density. The issue for demonstrating steady state operation is whether divertor function to control particle and heat flux is effective enough.