Balance of the stored energies sustained by the internal and edge transport barriers and effects of ELMs and L-H transitions in JT-60U

摘要

To understand key physics processes determining radial profiles of the kinetic plasma parameters in the advanced tokamak operation scenarios, correlations between the edge transport barrier (ETB) and the internal transport barrier (ITB) have been studied in the JT-60U tokamak device. It has been found that the edge pedestal poloidal beta, β_p-ped, increases almost linearly with the total poloidal beta, β_p-tot, over a wide range of the plasma current for type I ELMing H-mode plasmas, and this dependence becomes stronger with increasing triangularity. This dependence is not due to the profile stiffness, since the dependence is the same regardless of the existence of ITB. As the stored energy inside the ITB-foot radius (W_(ITB)) increases, the total thermal stored energy (W_(th) increases and then the pedestal stored energy (W_(ped)) increases. On the other hand, as W_(ped) increases, the ELM penetration expands more inwards and finally reaches the ITB-foot radius. At this situation, the ITB-foot radius cannot move outwards because of the erosion by ELMs. Then the fractions of W_(ITB)/ W_(th) and W_(ped)/ W_(th) become almost constant. It has also been found that the type I ELM expels/decreases the edge toroidal momentum larger than the edge ion thermal energy. The ELM penetration for the toroidal rotation tends to be deeper than that for the ion temperature and can exceed the ITB-foot radius. The ELM penetration is deeper for CO-rotating plasmas than CTR rotating plasmas. In both cases, the ELM penetration is deeper in the order of the toroidal rotation (V_t), the ion temperature (T_i) and then the electron temperature (T_e). The L-H transition also changes the V_t profile more significantly than the T_i profile. At the L-H transition, the pedestal Vt shifts into the CTR-direction deeply and suddenly without a change in 7], and then the pedestal V_t grows further together with a growth of the pedestal T_i in a slower timescale. Such changes in V_t by ELMs and L-H transitions may affect degradation/evolution of ITB s.