Feedback control of plasma density and heating power for steady state operation in LHD

• We upgraded a control system for steady state operation in LHD.
• This system contains gas fueling system and ICRF power control system.
• Automatic power boost system is also attached for stable operation.
• As a result, we achieved the long pulse up to 48 min in the electron density of more than 1 × 1019 m−3.

For steady state operation, the feedback control of plasma density and heating power system was developed in the Large Helical Device (LHD). In order to achieve a record of the long pulse discharge, stable plasma density and heating power are needed. This system contains the radio frequency (RF) heating power control, interlocks, gas fueling, automatic RF phase control, ion cyclotron range of frequency (ICRF) antenna position control, and graphical user interface (GUI). Using the density control system, the electron density was controlled to the target density and using the RF heating power control system, the RF power injection could be stable. As a result of using this system, we achieved the long pulse up to 48 min in the electron density of more than 1 × 1019 m−3. Further, the ICRF hardware experienced no critical accidents during the 17th LHD experiment campaign in 2013.