Complete suppression of neoclassical tearing modes with current drive at the electron-cyclotron-resonance frequency in ASDEX upgrade tokamak

Noninductive current drive has been performed in the tokamak ASDEX upgrade by injection of radiofrequency waves at the second harmonic of the electron -cyclotron frequency in order to suppress unwanted disturbances of the magn etic-field configuration. The current has been driven parallel [co-electron cyclotron current drive (ECCD)] and antiparallel (counter-ECCD) to the pla sma current to compare the effect of heating with direct current drive in t he magnetic island. For the first time it has been shown experimentally tha t total stabilization of neoclassical tearing modes is possible with co-ECC D. The experiments verify the role of direct current drive as opposed to lo cal heating.