Electron Thermal Transport Barrier and Density Fluctuation Reduction in a Toroidal Helical Plasma

A thermal transport barrier resulting in a high central electron temperature of $\sim 2\mathrm{keV}$ is established in the core of electron-cyclotron-resonance heated plasmas of the Compact Helical System Heliotron/Torsatron. The formation of the barrier is correlated with the reduction in the density fluctuations and with a structural change of the radial electric field profile at the barrier location. The results suggest that the decrease in fluctuation should contribute to a reduction of anomalous transport and a drastic increase in electron temperature at the barrier.