Footprint of the Magnetic Configuration in ECH Plasmas of the TJ - II Flexible

The configurational flexibility of the TJ-II Heliac has been upgraded with the commissioning of a mode of operation that allows changing the magnetic configuration dynamically: the currents feeding the different coil sets can be ramped during the discharge, which allows for, e.g., moving up or down the offset of the rotational transform profile. In these experiments the Ohmic transformer is also activated so as to counteract the induced currents. This capability can be used to investigate the effect of low order rational values of the rotational transform, ι/2π, in transport magnitudes, like the effective diffusivities, without altering considerably the magnetic shear. The experiments in plasmas created and sustained with Electron Cyclotron Resonance Heating show, in agreement with previous experience from the TJ-II, that such low order rational values of ι/2π do not deteriorate the effective heat diffusivity.