Stationary discharges with $H$-mode edge and internal transport barrier for energy, momentum, and particle transport have been obtained on ASDEX Upgrade. At a line averaged density of $4\times {10}^{19}{\mathrm{m}}^{-3\mathrm{}}$ an $H$ factor of $H_{\mathrm{ITER}89-P}=2.4\mathrm{}$ and ${\beta }_N=2\mathrm{}$ could be maintained for 6 s corresponding to 40 confinement times, limited only by the possible discharge duration. The $q$ profile is flat in the center and close to 1. Current diffusion calculations suggest that reconnection is required to clamp the safety factor at 1, which in the absence of sawteeth is explained by the strong fishbone activity.

• Received 29 October 1998

DOI:https://doi.org/10.1103/PhysRevLett.83.1787