  Recent experimental observations at JET show evidence of reduced ion
temperature profile stiffness, hypothesised to be due to concomitant low
magnetic shear (s) and significant toroidal rotational flow shear. Non-linear
gyrokinetic simulations are performed, aiming to investigate the physical
mechanism behind the observations. A comprehensive set of simulations are
carried out, comparing the impact on the ion heat flux of various parameters
that differ within the data-set. These parameters include q, s, rotation,
effect of rotation on the magnetohydrodynamic (MHD) equilibrium, R/L_n, beta_e,
Z_eff, and the fast particle content. The effect of toroidal flow shear itself
is not predicted by the simulations to lead to a significant reduction in ion
heat flux, due both to an insufficient magnitude of flow shear and significant
parallel velocity gradient destabilisation. It is however found that non-linear
electromagnetic effects due to both thermal and fast-particle pressure
gradients, even at low beta_e, can significantly reduce the profile stiffness.
A total of five discharges are examined, at both inner and outer radii. For all
cases studied, the simulated and experimental ion heat flux values agree within
reasonable variations of input parameters around the experimental
uncertainties.
