Electron cyclotron current drive at the second harmonic in the WT-3 tokamak.
Electron cyclotron current drive (ECCD) at the second harmonic (..omega.. = 2..cap omega../sub e/) is demonstrated for two types of plasma in the WT-3 tokamak. When microwave power P/sub EC/ is injected into a plasma after Ohmic heating (OH) power is shut down, the plasma current is sustained and ramped up by the EC wave only. Here 2..cap omega../sub e/ EC-driven current is generated by 2..cap omega../sub e/ EC heating of an energetic electron tail existing in the OH plasma. Further, when P/sub EC/ is injected into a microwave discharge plasma, 2..cap omega../sub e/ EC-driven plasma current is started up and 2..cap omega../sub 3/ ECCD plasma is formed without OH power. The 2..cap omega../sub e/ ECCD efficiency is the same order as that at ..omega.. = ..cap omega../sub e/, but the 3..cap omega../sub e/ EC-driven current is not generated, in contrast with the theoretical prediction.