Spontaneous L-mode plasma rotation scaling in the TCV tokamak

Predicting intrinsic plasma rotation and its shear, which often help stabilize plasma instabilities affecting plasma performance, is important for prospective fusion grade devices. Although rotation in ITER-like scenarios has been extrapolated from measured experimental plasma rotation data, little is understood about the underlying mechanisms governing either the generation or dissipation of momentum in a tokamak plasma. This paper reports on studies of intrinsic toroidal and poloidal plasma rotation from charge exchange spectroscopy using a low power diagnostic beam on the TCV tokamak [Tonetti , in Proceedings of the Symposium on Fusion Technology (1991), p. 587] that drives negligible toroidal velocity. In TCV, plasma behavior can be separated by the core and edge regions. In limited configurations, the core rotates in the counter-current direction and can reverse to the co-current direction with a < 10% increase in the plasma density. This is different for diverted configurations where the core rotates in the co-current direction reversing to the counter-current direction at higher plasma densities. For all these situations, core toroidal momentum is strongly transported by plasma sawteeth oscillations. In contrast, the toroidal edge rotation is close to stationary for limited discharges but evolves with plasma density for diverted configurations. Theoretical models that predict a change in momentum transport from turbulence have previously been suggested to provide a mechanism that might explain these phenomena. In this paper, mode activity that changes at the toroidal velocity reversal, is identified as a new possible candidate. In the absence of an available model that can explain these basic phenomena, this paper presents observations and, where possible, scaling of the rotation profiles with some of the major plasma parameters such as current, density and shape to guide the development of a physics model for use in improving the extrapolation of the rotation amplitude and profiles to future devices. (C) 2008 American Institute of Physics.