Analysis of internal transport barrier heat diffusivity from heat pulsepropagation induced by an ITB event in JT-60U reverseshear plasmas

Internal transport barrier (ITB) formation in the positive shear zone ofreverse shear (RS) plasmas in the JT-60U tokamak is described as a series ofITB events, which are abrupt in time and widein space variations of heat diffusivity, observed as the simultaneous rise and decay of the electrontemperature Te in two zones. A new source of heat pulse propagation(HPP) is found in RS plasmas. HPP is created by an ITB event. For the last ITBevent described in the present paper, the region of strong(~20 keV s-1) Te rise is initially well localized(~4 cm) in space. Later, a slow diffusive broadening of the risingTe perturbation is seen. Outward HPP is analysed in the region with~8 cm width fully located in the positive shear space zone. Values ofthe electron dynamic heat diffusivity as low as ~0.1 m2 s-1 arefound. A similar low value of the ion dynamic heat diffusivity (close to theneoclassical value) is obtained for ion HPP. An important consequence of HPPanalysis is the absence of electron and ion `heat pinch' in the ITB region.