Electron thermal transport barrier and density fluctuation reduction in a toroidal helical plasma

A thermal transport barrier resulting in a high central electron temperatur e of similar to 2 keV is established in the core of electron-cyclotron-reso nance heated plasmas of the Compact Helical System Heliotron/Torsatron. The formation of the barrier is correlated with the reduction in the density f luctuations and with a structural change of the radial electric field profi le at the barrier location. The results suggest that the decrease in fluctu ation should contribute to a reduction of anomalous transport and a drastic increase in electron temperature at the barrier. [S0031-9007(99)08825-0].