Ignitor Plasma Performance in the H-mode with New Scalings$^*$

Ignitor can operate with a double-null configuration with the relevant X-points laying close to the first wall, {$B_{T} \simeq 13$ T, $I_{p} \simeq 9$ MA}, {$R_{0} \simeq 1.32$} m, {$a \simeq 0.44$} m. The power threshold to access the H-regime has been found to be considerably lower on the basis of recent scalings\footnote {D.~C.\textsc{} McDonald et al., \textit{Plasma Phys. Control. Fusion} \textbf{48}, A439 (2006);} than originally assessed. The expected plasma parameters in this regime are estimated by using a global O-D model. The operating space corresponding to $Q\simeq10$ is verified to be relatively broad, even considering the pessimistic case of rather flat density profiles, and far from density and $\beta$ operational limits. Moreover, the analysis of JET experimental data\footnote{H.~Weisen et al., \textit{Plasma Phys. Control. Fusion} \textbf{48}, A457 (2006);} indicates that relatively peaked density profiles (e.g. $n_0/\langle n \rangle \simeq 1.5$) can be obtained in the H-regime. With these profiles, the attainable plasma parameters are found to improve considerably and values of $Q$ much larger than 10 can be attained. The adoption of scalings\footnote{J.~W.~Cordey et al. \textit {Nucl. Fusion} \textbf{45}, 1078 (2005).} for the energy confinement time with a weak dependence on $\beta$ does not change the operating space significantly in the case of Ignitor.\\ $^*$Work supported in part by ENEA of Italy and by the US DOE.