Spontaneous tokamak rotation: observations turbulent momentum transport has to explain
Seminar Room 1, Newton Institute
Ideal tokamaks have axisymmetric magnetic fields that, by symmetry, cannot impart toroidal angular momentum. Yet, even without obvious external sources of momentum, such as neutral-beams, they rotate at speeds up to a substantial fraction of the ion thermal speed. This spontaneous rotation is an unequivocal signature of momentum transport (presumably turbulent) *up* the velocity gradient --- that is, in the opposite direction to any supposed shear viscosity. Theoretical suggestions for the mechanisms producing spontaneous rotation exist; but even qualitative confrontation of theory with experiment is at a rudimentary stage. This presentation will summarize some key experimental observations that require explanation. Understanding the spontaneous rotation is vital for future devices like ITER, where beam-driven rotation will be small, and might be relevant also in the space and astrophysical context.