Indirect measurement of the poloidal rotation in the core of ASDEX Upgrade plasmas with charge exchange recombination spectroscopy

where ∇pα denotes the radial pressure gradient, eZα the charge, nα the density and upol,α and utor,α the poloidal and toroidal rotation velocities of the species α . Bpol and Btor are the poloidal and toroidal magnetic field components determined from the magnetic equilibrium reconstruction. One of the most commonly used diagnostic to evaluate the ion quantities is active charge exchange recombination spectroscopy (CXRS), which measures the line-emission resulting from the charge exchange process between fully stripped impurity ions with neutrals from the highly energetic neutral beam injection (NBI) sources. At the plasma edge, where the temperatures are low, the direct observation of upol is a standard technique (see e.g. [2]). In the plasma core, however, the direct measurement of upol is more challenging due to practical geometry and signal to noise issues associated with the poloidal lines-of-sight (LOS) as well as atomic physics issues. The energy dependence of the charge exchange cross-sections [3] in combination with the finite lifetime of excited atomic states lead to an apparent rotation in the poloidal direction [4] exceeding the desired poloidal rotation at high temperatures and magnetic fields.