Synergy Current Driven by Combined Lower Hybrid Wave and Different Polarized Electron Cyclotron Wave in Tokamak Plasma

The synergy current driven by combined lower hybrid wave (LHW) and electron cyclotron wave (ECW) in two different polarizations is studied. It is shown that improvement of the current drive efficiency can be obtained during the synergy current drive, using either the fundamental ordinary mode (1O-mode) or the second harmonic extraordinary mode (2X-mode) ECW. Detailed comparison of using the two modes reveals that the 1O-mode is more effective than the 2X-mode. It is also found that the synergy current driven by LHW and 2X-mode ECW is more likely to become negative when the power of ECW is higher than that of LHW.