Third harmonic EC heating of ELMy H-mode in TCV
Ohmic H-mode discharges in the Tokamak Configuration Variable (TCV) have recently been heated for the first time by electron cyclotron (EC) waves at the 3rd harmonic (X3) at full power. New edge localized mode (ELM) behaviour has been found, with larger amplitudes at lower frequency than are typical in ohmic H-modes. This new regime required the full available X3-EC Heating (X3-ECH) power to avoid the ELM-free phase, which occurred when less heating power was applied. The energy loss per ELM can be up to 15% of the total stored energy, with values in the range 4-5% being typical of the smaller ELMs usually found in the ohmic H-mode regime. Despite these high-energy losses, the plasma temperature raises significantly in the X3 heated H-modes, doubling the stored energy from its ohmic value. The confinement time decreases when the ECH is applied, but can recover its ohmic H-mode value later in the discharge depending on the EC wave coupling. It is still not possible to provide an unambiguous classification of these ELMs as Type I.