Analysis of internal transport barrier heat diffusivity from heat pulse propagation induced by an ITB event in JT-60U reverse shear plasmas

Internal transport barrier (ITB) formation in the positive shear zone of reverse shear (RS) plasmas in the JT-60U tokamak is described as a series of ITB events, which are abrupt in time and wide in space variations of heat diffusivity, observed as the simultaneous rise and decay of the electron temperature T e 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 ITB event described in the present paper, the region of strong (~20 keV s -1 ) T e rise is initially well localized (~4 cm) in space. Later, a slow diffusive broadening of the rising T e perturbation is seen. Outward HPP is analysed in the region with ~8 cm width fully located in the positive shear space zone. Values of the electron dynamic heat diffusivity as low as ~0.1 m 2 s -1 are found. A similar low value of the ion dynamic heat diffusivity (close to the neoclassical value) is obtained for ion HPP. An important consequence of HPP analysis is the absence of electron and ion `heat pinch' in the ITB region.