GYRORADIUS SCALING OF HELIUM TRANSPORT

The scaling of the transport rate of helium ash with normalized gyrora dius has been measured for the first time, utilizing ELMing H-mode pla smas on the DIII-D tokamak. The helium diffusivity is found to scale i n a gyro-Bohm-like manner, similar to the thermal diffusivity. Even th ough the extrapolation in normalized gyroradius from DIII-D to a react or-grade device is large, sensitivity studies indicate that helium ash dilution in such a device will be primarily dependent on the helium e xhaust efficiency at the plasma edge and not on the core transport rat es.