Characteristics of toroidal plasma rotation have been experimentally
investigated using charge exchange recombination spectroscopy in the ASDEX
Upgrade tokamak. Ion cyclotron resonance frequency (ICRF) heating is found
to cause a reduction of the toroidal rotation velocity, Vφ, driven by neutral beam
injection (NBI) in the co- and counter-current directions. The reduction of
plasma rotation is attributed to an increasing momentum diffusivity connected
with the confinement degradation by the additional ICRF power flux, and not
to an ICRF induced toroidal force related to radial non-ambipolar transport of
resonant particles. Toroidal momentum transport is found to be anomalous in
various plasma regimes including standard and improved H-modes and ioninternal
transport barrier (ITB) plasmas. In the inner half of those plasmas,except for high density H-modes with on-axis NBI only, the momentum
diffusivity, χφ, is found to be similar to the ion and electron heat diffusivities, χi and χe. In the outer half region, χφ becomes smaller than χi, while χφ is still
comparable with χe except for ITB plasmas. It is found that the normalized
gradient length of the toroidal rotation velocity, R/LVφ is smaller than that of
the ion temperature, R/LTi , in H-modes and ITB plasmas. |