INVESTIGATION OF HIGH-N TAE MODES EXCITED BY MINORITY-ION CYCLOTRON HEATING IN JT-60U

Toroidicity-induced Alfven eigen (TAE) modes are observed during minor ity-ion cyclotron resonance heating (ICRH) in the JT-60U. The toroidal mode numbers of TAE modes are identified as 7, 8, 9, 10 and 11 from t he Doppler shift in the TAE modes with scanning toroidal rotation at a plasma current of 3 MA. The toroidal mode number of TAE modes tends t o increase during a giant sawtooth by ICRH with a decreasing safety fa ctor for the central region. The TAE mode number increases with plasma current, so that nine TAE modes are observed sequentially during a gi ant sawtooth at a plasma current of 4 MA, where the maximum toroidal m ode number is estimated to be at least 13. There are no Alfven continu um gaps for TAE modes in the safety-factor ranges of i - 1/2n < q < i + 1/2n, (i = 1,2, 3,...), except for the gaps in ellipticity-induced A lfven eigen (EAE) modes, where n is the toroidal mode number of TAE mo des. Therefore, control of the q profile might provide a means of avoi ding TAE modes, as long as the pressure gradient of the high-energy io ns is localized.