Confinement quality as good as ELM-free H-mode at densities substantially above the Greenwald density limit ( ${\overline{n}}_{e,0\mathrm{}}/n_{\mathrm{GW}}=1.4\mathrm{}$) has been obtained in discharges with a radiative boundary under quasistationary conditions for 20 times the energy confinement time. This is achieved by optimizing the gas-fueling rate of RI-mode discharges which tailors their favorable energy confinement and leads to discharges with beta values just below the operational limit ${\beta }_n=2\mathrm{}$ of TEXTOR-94, thereby effectively avoiding confinement back transitions or disruptions. In addition, this high-density regime is favorable for helium removal and results in figures of merit ${\tau }_{p,He}^{*}/{\tau }_E\approx 10–15$, relevant for a future fusion power reactor.

• Received 31 March 2000

DOI:https://doi.org/10.1103/PhysRevLett.85.2312