Evidence of inhomogeneous thermal transport in RTP

There are strong indications that the radial electron thermal diffusivity is not a smooth function of the radius, but shows strong local variations. To investigate this irregularity systematically, a number of dedicated experiments have been carried out in the RTP tokamak: intense central heating, pellet ablation experiments, perturbative transport studies and steady state off-axis heating. The crucial diagnostic in these experiments is the Thomson scattering system, with a radial resolution of 1% of the minor radius. In sawtoothing plasmas a transport barrier has been identified near the sawtooth inversion radius. With steady state off-axis heating, hollow current density profiles have been sustained, and the region of reversed magnetic shear is characterized by very low thermal transport.