Heuristic model for the power threshold of the L-H transition

Guided by the recent experimental finding of the key role played by the ion heat channel in the transition from low (L) to high (H) confinement mode (Ryteret al2014Nucl. Fusion54 083003, Schmidtmayret al2018Nucl. Fusion58 056003), the present phenomenological model of the power threshold for the L-H transition is developed by combining the energy equipartition between electrons and ions, and the L-mode scaling of the energy confinement time. This heuristic model describes with continuity the transition of the power threshold from the low- to the high-density branches and clarifies the origin of the main dependence of the power threshold on the plasma current in the low density branch.