Overview of the Large Helical Device

Abstract

The Large Helical Device (LHD) experiments have started after aconstruction period of eight years, and two experimental campaigns wereperformed in 1998. The magnetic field was raised up to 2.75 T at a magneticaxis position of 3.6 m at the end of the second campaign. In the thirdcampaign, started in July in 1999, the plasma production with ECH of 0.9 MWand auxiliary heating with NBI of 3.5 MW have achieved an electrontemperature of 3.5 keV and an ion temperature of 2.4 keV. The maximumstored energy has reached 0.75 MJ with an averaged electron density of7.7×1019 m-3 by hydrogen pellet injection. The ICRF heatinghas sustained the plasma for longer than 2 s and the initial stored energyof the NBI target plasma has increased from 0.27 MJ to 0.335 MJ. The majorcharacteristic of the LHD plasma is the formation of the temperaturepedestal, which leads to some enhancement of energy confinement over theISS95 scaling law. The confinement characteristic is gyro-Bohm and themaximum energy confinement has reached 0.28 s. The LHD has also shown itshigh potentiality for steady-state operation by realizing a 22 s dischargein the second campaign.