When the applied heating power is raised above some threshold, the plasma transitions from the low-confinement mode (L-mode) to the H-mode where the energy confinement time approximately doubles in magnitude.
A possible explanation concerns increased flow shear which suppresses turbulent transport at the plasma edge.
for tokamak L-mode is given empirically by the ITER89-P scaling expression:[2] where It was discovered in 1982 on the ASDEX tokamak that when the heating power applied is raised above a certain threshold, the plasma transitions spontaneously into a higher-confinement state where the energy confinement time approximately doubles in magnitude,[1] albeit still showing an inverse dependence on heating power.
Due to its improved confinement properties, H-mode quickly became the desired operating regime for most future tokamak reactor designs.
The physics basis of ITER rely on the empirical ELMy H-mode energy confinement time scaling.