Indirect measurement of poloidal rotation using inboard–outboard asymmetry of toroidal rotation and comparison with neoclassical predictions
An alternative experimental spectroscopic measurement of poloidal plasma rotation in toroidally confined plasmas is proven effective in the TCV tokamak. Charge exchange recombination measurements of the toroidal rotation profile over the full mid-plane plasma diameter are used to infer the complete bi-dimensional flow structure of the intrinsic C6+ impurity, which includes its poloidal component. For divergence free flows, the difference between the toroidal rotation frequency ft = ut/R at the inboard and outboard locations on the same flux surface is proportional to the poloidal rotation. This indirect measurement provides increased accuracy as the measured quantity ft,in − ft,out ≈ 4qup/Raxis (q is the local safety factor) is larger than the intrinsic uncertainties of a direct spectroscopic measurement of poloidal velocity. The method is applied in a variety of TCV ohmic and electron cyclotron heated L-mode plasmas in the banana-plateau collisionality regime (0.2 < ν∗ii < 2.4). In the radial range of normalized poloidal flux ρψ < 0.8, an impurity poloidal velocity of up = 0.5–2.5 kms−1 is observed, always in the electron diamagnetic drift direction. The measurements are compared with neoclassical calculations and they agree in magnitude and sign to within <1 kms−1.