No abstract

In the Phaedrus-T tokamak ͓R. A. Breun et al., Fusion Technol. 19, 1327 ͑1991͔͒, Alfvén waves are indirectly driven by a fast wave antenna array. Small fractions of minority ions are shown to have a large effect on the Alfvén spectrum, as measured at the edge. An ion-ion hybrid Alfvén mode has been identified by measuring dispersion properties. Landau damping is predicted to be large and spatially localized. These Alfvénic waves are experimentally shown to generate correlated electron heating and changes in density near the core of the tokamak plasma. Fast wave antenna fields can mode convert at a hybrid Alfvén resonance and provide a promising route to spatially localized tokamak heating and current drive, even for low effective ionic charge Z eff Ϸ1.3-2.

No abstract

The first experimental evidence of Alfven Wave Current Drive (AWCD) in a tokamak is 'shown. In a low-density experiment, an estimated 20-35' kA out of 65 kA total current; or 30%-55% of the total current has been driven. The estimated efficiency for current driven per unit RF input power is approximately ZcnZP~=0.2 A/W, which is near the predicted efficiency, and corresponds to the commonly used figure of merit, n,R0Z&/Z',==0.4X 10" A mm2 W-l; where n, is plasma density and R, is the major radius. The 'significant 30%:40% drop in loop voltage observed cannot be explained by any plausible increase in electron temperature T, , or decrease in inductive plasma energy, or changes in plasma resistivity. Independently measured loop voltage, T, , effective ionic charge Z&, and plasma inductance and'resistance are all consistent with&is conclusion. 0 2995 American Institute of Physics.

In the Phaedrus-T tokamak ͓R. Majeski et al., Phys Fluids B 5, 2506 ͑1993͔͒, Alfvén waves are indirectly driven by a fast wave antenna array. Small fractions of minority ions can couple Alfvén and ion-ion hybrid waves and have a large effect on the wave numbers accessible for a given launched frequency. A discrete spectrum and toroidal damping for these modes has been identified by measuring dispersion properties at the edge. Landau damping is predicted to be large and spatially localized and to be responsible for the experimentally observed electron heating ͑T. Intrator et al., ''Alfvén ion-ion hybrid wave heating in the Phaedrus-T tokamak,'' to appear in Phys. Plasmas͒ and current drive near the core of the tokamak plasmas.