Time Behavior of Heat Diffusivity during L-H-L Transitions in JT-60U

The L-H-L transitions have been analyzed mainly for high-field pulses (B t ≈4 T) in JT-60U. The simultaneous response of electron temperature T e has been clearly observed during L-H-L transitions over a wide plasma region. This T e evolution is described as the result of the fast jump of electron heat diffusivity, δχ e, over the wide plasma region. Values of δχ e were obtained as 0.5 m2/s < | δχ e | < 1 m2/s, which usually increase with radius. The simultaneous response of ion temperature T i was also observed to be that of similar to the T e response. The jump of ion heat diffusivity, δχ i, is similar to that of δχ e and usually increases with radius, as does δχ e. In a low-field pulse (B t ≈2.5 T), | δχ i | is as large as 2 m2/s. Values of δχ are consistent with the change of the energy confinement time during transitions.