Quantifying Profile Stiffness

Profile stiffness is quantified using a simple technique. The approach is tested on a paradigmatic numerical stiff transport model for one field (particles). The stiffness is found to exhibit radial structure and to depend on collisionality, which might help explaining the observed lack of stiffness in stellarators, as compared to tokamaks. The extension of this approach to heat transport requires some care. A proposal for a stiffness quantifier for heat transport is presented, and tested on data from the TJ-II stellarator.