First dynamic magnetic configuration scans in ECRH plasmas of the TJ-II Heliac

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, for example, moving up or down the offset of the rotational transform profile. The first discharges in this operation mode have been designed to investigate the effect of low order rational values of the rotational transform, , in low magnetic shear plasmas created and sustained with electron cyclotron resonance heating. The main magnetic resonances (8/5 and 5/3 in this work) do not deteriorate confinement except occasionally in a short, transient manner that is accompanied by a magnetic event with a clear frequency splitting.