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 pow er. However, experiments have shown that a minimum level of input powe r is required to access and sustain the H-mode regime. This paper stud ies the impact on ITER operation of the presently available scalings o f this minimum input or threshold power for both the direct L- to H- a nd reverse H- to L-mode transitions. We present scenarios for access i nto the H-mode, for maintaining the plasma in H-mode and for the fusio n 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 th e L- to H-mode transition with a reduction of a factor of two for the reverse transition has severe consequences on ITER operation and perfo rmance and various methods to quantify this impact are presented. We c onclude, however, that the ITER mission and physics objectives remain compatible with such a scaling.