Inserting a positively biased electrode to just inside the Phaedrus-T tokamak limiter results in typical H mode behaviour (i.e. Hα or Dα drop, density rise, increase in stored energy, profile steepening, and reduction of edge turbulence and radial transport) in deuterium, hydrogen and helium discharges. Hα or Dα emission suggests that the improvement in particle confinement with H mode is poloidally asymmetric, with the greatest improvement occurring on the low field side. The radial conductivity is examined and measured values are compared with theory

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.

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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.

Electrostatic end plugging is observed in a completely axisymmetric, three cell tandem mirror under conditions where the central-cell plasma density is always larger than the end-cell density. A factor of 4 increase in the central-cell density, to a maximum of 1.2×1013 cm−3 with simultaneous plasma beta of 13%, occurs upon application of the end plugging potential. Ion confining potentials of 25 V and 80 V at the two ends of the device, respectively, result in a factor of 2.5 increase in the axial confinement time for Tic =40 eV in agreement with the collisional flow model for ion confinement. The non-Boltzmann ion confining potential is caused by electron heating in the end cells by rf near the ion-cyclotron frequency. The initial central-cell density rise is caused by an increase in the ionization rate that occurs because of an increase in the electron temperature. The density remains high throughout the end-cell heating pulse as a result of increased particle confinement time. There is no nonambipolar radial ion loss in the core plasma (r≤16 cm) but inward radial transport of ions is observed at a rate consistent with ion–neutral collisions and a radial electric field in the negative radial direction. Steady-state thermal-barrier-like potential dips that are in agreement with the Boltzmann model for potentials are observed in the transitions between the central cell and the end cells.