Confinement capability of ITER-EDA design

Confinement capability of the ITER-EDA (R=7.75 m, I=25 MA) operational scenarios is evaluated and compared with the ITER CDA (R=6 m, 22 MA). The ignition capability of ITER EDA is somewhat higher than that of CDA by a factor of 1.1-1.2 with empirical power law scalings and by a factor of 1.5-2 with offset linear scalings. Simulations with the RLW /spl chi/(/spl nabla/T/sub e/)/sub crit/ model show that both the EDA and CDA scenarios operates in L-mode, however CDA ignition margin is much smaller. With empirical scalings, the required L-mode confinement enhancement factor [H=/spl tau//sub E///spl tau//sub E/(scaling)] corresponding to, for example, ITER89-P L-mode scaling would be 1.5-1.6 in ITER EDA relative to 1.8 in CDA for 10% He (plus 1% Be) concentration. At a higher concentration of He of 20-25%, the confinement capability is deteriorated and the required confinement enhancement factor (over empirical L-mode scalings) is /spl ges/2. The Ohmic confinement time is a factor of two higher in the EDA design (as compared to the CDA), yielding a strong reduction in the auxiliary power required to reach ignition. In 1.5-D simulations with L-mode enhancement factors of H/spl ges/1.2 allowed ohmic ignition with 25 MA, ignition was aided by initially peaked density profiles (and low He content) during the start-up.