Suppression of large amplitude driven sawteeth by lower hybrid current drive

A characteristic feature of ion cyclotron minority heating is the excitation of large amplitude sawteeth due to central power deposition and good electron‐ion coupling. A similar phenomenon is expected to occur in a fusion reactor, where energetic alpha particles at the center of the plasma will also drive large amplitude sawteeth. By using ion cyclotron heating (ICH) in conjunction with lower hybrid current drive (LHCD) the suppression of large amplitude sawteeth could be studied in a controlled fashion. With P(ICH)<0.8 MW and P(LHCD)<0.8 MW, and ΔTe/Temax =0.2, the lower hybrid power necessary to suppress the large amplitude sawteeth was approximately the same as that required to suppress ohmic sawteeth at the same line average electron density. In addition, it is found that LHCD does not degrade ICH discharges, nor does ICH degrade the efficiency of lower hybrid current drive.