Long-spatial-scale density fluctuations with a wave number of the order of 1 cm−1 were suppressed in the internal transport barrier (ITB) region of a JT-60U reversed magnetic shear plasma, after a cold pulse was induced by the shallow pellet injection at the plasma edge. The particle and ion heat diffusivities are reduced with the suppressed fluctuations. The reduction of the electron heat diffusivity is observed only transiently in the inner ITB portion around the layer of the density fluctuation measurement during the cold pulse propagation and it is slower (∼ 15 ms) than the reduction of the density fluctuation level (< 5 ms). In the outer ITB portion, the electron heat diffusivity increases transiently. These results indicate decoupling of the electron heat transport and the long-spatial-scale density fluctuations.
Cold pulse experiments in plasma with an electron internal transport barrier on LHD