Dependence of intrinsic torque and momentum confinement on normalized gyroradius and collisionality in the DIII-D tokamak

The dependence of intrinsic torque and momentum confinement time on normalized gyroradius ( ρ*) and collisionality ( ν*) has been measured in the DIII-D tokamak. The intrinsic torque normalized to temperature is found to have ρ* and ν* dependencies of ρ*−1.5±0.8 and ν*0.26±0.04. This dependence on ρ* is unexpectedly favorable (increasing as ρ* decreases). The choice of normalization is important, and the implications are discussed. The unexpected dependence on ρ* is found to be robust, despite some uncertainty in the choice of normalization. The dependence of momentum confinement on ρ* does not clearly demonstrate Bohm or gyro-Bohm like scaling, and a weaker dependence on ν* is found. The calculations required to use these dependencies to determine the intrinsic torque in future tokamaks such as ITER are presented, and the importance of the normalization is explained. Based on the currently available information, the intrinsic torque predicted for ITER is 33 N m, comparable to the expected torque available from neutral beam injection. The expected average intrinsic rotation associated with this intrinsic torque is small compared to current tokamaks, but it may still aid stability and performance in ITER.