Initial ICRF heating experiments on the LHD

The final goal of Ion Cyclotron Range of Frequency (ICRF) heating on the Large Helical Device (LHD) is characterized by its high power (up to 12MW) and by steady state operation (30 minutes). Initial ICRF heating experiments were carried out using a pair of loop antemas in the 2nd experimental campaign in 1998. The ICRF heating power was applied to an ECH-produced plasma at an RF power level of 300 kW for 0.2 seconds. An applied frequency of f=25.6 MHz was selected. A cyclotron resonance layer of hydrogen ions was located at the half minor radius during operation at B=1.5 T. A mode conversion layer of a He plasma with a minority of hydrogen ions was located between the magnetic axis and the last closed magnetic flux. The plasma stored energy was observed to increase to twice that of the ECH plasma (PECH=300 kW). The plasma stored energy of the ECH target plasma was 11-13 kJ at an average electron density of ne=8–9×1018 m−3 and a central electron temperature of Te0=400 eV. The plasma stored energy increased by 13 kJ with the application of ICRF heating at ne=7–8×1018 m−3 and Te0=700 eV. A strong electron heating via mode conversion was observed at a higher minority ratio of hydrogen ions.