Impact of H-mode power threshold on ITER performance and operation

H-mode operation is projected to be needed in ITER in order to achieve its objectives of sustained burn for 1000 s with 1.5 GW of fusion power. However, experiments have shown that a minimum level of input power is required to access and sustain the H-mode regime. This paper studies the impact on ITER operation of the presently available scalings of this minimum input or threshold power for both the direct L- to H- and reverse H- to L-mode transitions. We present scenarios for access into the H-mode, for maintaining the plasma in H-mode and for the fusion power shutdown with the reverse transition into L-mode. The commonly used empirical scaling p(thr)(L-H) = 0.044<(n)over bar (e)>BTS for the L- to H-mode transition with a reduction of a factor of two for the reverse transition has severe consequences on ITER operation and performance and various methods to quantify this impact are presented. We conclude, however, that the ITER mission and physics objectives remain compatible with such a scaling.