Electron cyclotron current drive at the second harmonic in the WT-3 tokamak

Electron cyclotron current drive (ECCD) at the second harmonic ({ω}=2Ωₑ) is demonstrated for two types of plasma in the WT-3 tokamak. When microwave power PEC 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 2Ωₑ EC-driven current is generated by 2Ωₑ EC heating of an energetic electron tail existing in the OH plasma. Further, when PEC is injected into a microwave discharge plasma, 2Ωₑ EC-driven plasma current is started up and 2Ω₃ ECCD plasma is formed without OH power. The 2Ωₑ ECCD efficiency is the same order as that at {ω}=Ωₑ, but the 3Ωₑ EC-driven current is not generated, in contrast with the theoretical prediction.