ELMing H-mode accessibility in shaped TCV plasmas

The H-mode regime is easily reached with ohmic heating only in a wide range of TCV plasma parameters. However, the plasma usually enters an ELM free H-mode phase after the LH transition, leading to a high density disruption. Therefore, the access to a stable ELMy regime requires an LH transition directly leading to an ELMy phase. A 'gateway' to the ELMy regime was found in TCV ohmic discharges. Although small in terms of plasma control parameter ranges, this 'gateway' is well defined and robust against changes in wall conditioning for instance. Once in the ELMing regime, the plasma was successfully driven in a much wider range of plasma parameters, whilst remaining in this better confinement mode. (author)