Current profile tailoring using localized electron cyclotron heating in highly elongated TCV plasmas
Radially localized electron cyclotron heating (ECH) at the 2nd harmonic (X2) is used to tailor the current profile through the modification of the temperature, and hence conductivity, profiles. The optimal conditions for current profile broadening are investigated and applied to decrease the plasma internal inductance at constant plasma current. Highly elongated plasmas are thus created at low current, where they are vertically unstable with peaked Ohmic current profiles, using active current profile broadening by far off-axis X2 ECH to ensure the vertical stability of IV the plasma. Central 3rd harmonic (X3) ECH is also applied and its impact on the current profile is described. The magnetohydrodynamic activity and in particular the replacement of the sawtooth by a multi-harmonics mode, resonant on the q = 1 surface and observed at high density and low internal inductance, is investigated.