In the empirical model developed by Y. Shimomura [1], it is assumed that plasma makes a transition from L-mode to H-mode when the power crossing the separatrix () rises above a power threshold ():
The power threshold for the transition to H-mode is calculated using the following formula,
where AH is the hydrogenic mass in AMU, is the vacuum
toroidal magnetic field at major radius R along the flux surface in
Tesla, R is the major radius in meters, is the line
average density in units of 1020 m-3 and a is the minor radius in meters. The RMS deviation of this model is 27%.