No abstract available

[en] H-modes operated at higher l_i with the current ramp down have shown higher energy confinement with higher density. The H-factor evaluated for the core plasma depends strongly on l_i, with the relation of H_89core ∼ l_i^0.74 for the case without sawtooth activities. Center peaked profiles of electron density and electron temperature are obtained in high l_i H-modes. While the peripheral current density profiles are largely modified by the current ramp, the pedestal pressure is not significantly changed. Thus, the increased density in high l_i H-modes is attributed to the peaked density profile with no explicit difference in pedestal profiles. It was found for the first time that the electron heat diffusivity is reduced at the centre in high l_i case, resulting in the centre peaked T_e profile while the T_i profiles are approximately stiff. (author)

[en] Full text: The pedestal pressure and energy confinement of H-mode plasmas were improved by the installation of ferritic steel tile (FST) in JT-60U. As the fast ion loss decreased, the H-mode pedestal temperature (and pressure) increased by ∼20-25% and the H-factor is increased by ∼ 20%. The ratio of ELM frequency to the power crossing the separatrix tends to become lower accompanied by larger type-I ELM spike. The experiments have shown that the energy confinement can be improved with the increase in the pedestal pressure accompanied by decreasing the fast ions loss ratio and/or enhancing the toroidal rotation in the co-direction. In JT-60U, the FST was installed in the vacuum vessel to reduce the toroidal field (TF) ripple ratio in 2005. In this study, comparing between the plasmas with and without FST, the effects of the fast ions loss and the toroidal rotation on the pedestal and core confinement properties are examined. At the identical plasma configuration between the discharges with and without FST, the pedestal temperature in case with FST can be raised by ∼20-25% compared to the case without FST at a given pedestal density. Larger type-I ELM spikes appear due to the increase in the pedestal pressure in case with FST. The ELM frequency normalized by the power crossing the sepratrix becomes relatively lower at a given line-averaged electron density. At a given absorbed power and pedestal density, the ion temperature profile becomes higher by ∼20% over the whole range of plasma core in case with FST. The stored energy also becomes larger by ∼20%. The ion temperature gradient in the ETB region becomes steeper by ∼5% and the pedestal width becomes wider by ∼10% with decreasing the fast ion loss fraction by ∼20%. After the FST installation, the toroidal rotation profile is shifted to the co-direction over the whole radial range including the plasma edge. The energy confinement can be improved as the fast ion loss fraction decreases. However, the toroidal rotation shifts to the co-direction monotonically together with the reduction of the fast ion loss. Since the radial electric field is influenced by the fast ion loss and toroidal rotation, the role of the toroidal rotation on the pedestal structure distinguished from that of fast ion loss should be analyzed in the next step study. (author)

No abstract available

[en] For the purpose of stable plasma equilibrium control and detailed analysis, it is essential to reconstruct an accurate plasma boundary on the poloidal cross section in tokamak devices. The Cauchy condition surface (CCS) method is a numerical approach for calculating the spatial distribution of the magnetic flux outside a hypothetical surface and reconstructing the plasma boundary from the magnetic measurements located outside the plasma. The accuracy of the plasma shape reconstruction has been assessed by comparing the CCS method and an equilibrium calculation in JT-60SA with a high elongation and triangularity of plasma shape. The CCS, on which both Dirichlet and Neumann conditions are unknown, is defined as a hypothetical surface located inside the real plasma region. The accuracy of the plasma shape reconstruction is sensitive to the CCS free parameters such as the number of unknown parameters and the shape in JT-60SA. It is found that the optimum number of unknown parameters and the size of the CCS that minimizes errors in the reconstructed plasma shape are in proportion to the plasma size. Furthermore, it is shown that the accuracy of the plasma shape reconstruction is greatly improved using the optimum number of unknown parameters and shape of the CCS, and the reachable reconstruction errors in plasma shape and locations of strike points are within the target ranges in JT-60SA

[en] Full text: A new hybrid kinetic trapped electron model is developed for electrostatic full-f gyrokinetic simulations. The model is verified by computing the ion and electron neoclassical transport and the linear ion temperature gradient driven trapped electron mode (ITG-TEM) stability, in which collisional TEM stabilization shows an isotope effect. An impact of kinetic electrons on the ITG turbulence is investigated by comparing ITG turbulence simulations with adiabatic electrons and with kinetic electrons. It is found that in the kinetic electron case, resonant passing electrons transport at mode rational surfaces generates corrugated density profiles, and the resulting microscopic radial electric field E_r sustains nonlinear critical temperature gradients above linear ones. This is qualitatively different from the so-called Dimits shift sustained by turbulence driven zonal flows in the adiabatic electron case. In the toroidal angular momentum balance, kinetic trapped electrons enhance the field term stress, which is characterized by the phase difference between the perturbed distribution and the toroidal electric field, and thus reversed between the adiabatic and kinetic electron cases. It is also found that the field term stress and the resulting intrinsic rotation is reversed between the ITG turbulence and the TEM turbulence. (author)

[en] Dependence of the energy confinement in ELMy H-mode tokamak on the beta has been investigated for a long time, but a common conclusion has not been obtained so far. Recent non-dimensional transport experiments in JT-60U demonstrated clearly the beta degradation. A database for JT-60U ELMy H-mode confinement was assembled. Analysis of this database is carried out, and the strong beta degradation consistent with the above experiments is confirmed. Two subsets of ASDEX Upgrade and JET data in the ITPA H-mode confinement database are analysed to find the origin of the various beta dependences. The shaping of the plasma cross section, as well as the fuelling condition, affects the confinement performance. The beta dependence is not identical for different devices and conditions. The shaping effect, as well as the fuelling effect, is a possible candidate for causing the variation of beta dependence

[en] The driving mechanism of toroidal rotation and the momentum transport are studied, utilizing nearperpendicular neutral beam injection (PERP-NBI), co tangential and counter tangential NBI in JT-60U. Main results are as follows: (i) fast ion losses due to the toroidal field ripple induce the toroidal rotation in the direction antiparallel to the plasma current, i.e. counter (CTR) direction in the peripheral region, (ii) the magnitude of CTR rotation increases with increasing the ripple loss power in the peripheral region. (iii) Diffusive and non-diffusive terms of momentum transport are evaluated from the transient analysis by using the momentum source modulation experiment. Fast ion losses which locally induce the edge CTR rotation have been used as a novel momentum source. (iv) Parameter dependence of these transport coefficients i.e. the toroidal momentum diffusivity χ_φ and the convection velocity V_conv, and the relation between heat and momentum diffusivities are investigated in L and H-mode plasmas systematically. The toroidal momentum diffusivity increases with increasing heating power, and decreases with increasing the plasma current in L-mode plasmas. The H-mode exhibits momentum diffusivity better than L-mode. Experiments indicate a positive correlation between the momentum and thermal transport at constant density. (v) We have also found that toroidal rotation velocity profiles in low .. plasmas can be almost explained by momentum transport considering diffusivity and convective velocity estimated from the transient momentum transport analysis. (author)

[en] The degradation of energy confinement with increased toroidal beta β_T was shown by non-dimensional analysis in JT-60U. The dependence of the energy confinement on β_T was examined by both the JT-60U ELMy H-mode confinement database and the dedicated experiment on a single β_T scan while ρ_T* and ν^* were kept fixed as well as the other magnetic geometrical parameters. In both cases, the degradation of energy confinement with increasing β_T was observed, satisfying the relation of B_Tτ_E ∝β_T^-(0.6-0.7). This dependence is a little weaker than that predicted by the IPB98(y, 2) scaling. The fusion power production rate was estimated to increase in proportion to β_T^0.3-0.4B_T

[en] The pedestal pressure and energy confinement of H-mode plasmas were improved by the installation of ferritic steel tile (FST) in JT-60U. As the fast ion loss decreased, the H-mode pedestal temperature (and pressure) increased by ∼20-25% and the H-factor is increased by ∼20%. The ratio of ELM frequency to the power crossing the separatrix tends to become lower accompanied by larger type-I ELM spike. The experiments have shown that the energy confinement can be improved with the increase in the pedestal pressure accompanied by decreasing the fast ions loss ratio and/or enhancing the toroidal rotation in the co-direction. In JT-60U, the FST was installed in the vacuum vessel to reduce the toroidal field (TF) ripple ratio in 2005. In this study, comparing between the plasmas with and without FST, the effects of the fast ions loss and the toroidal rotation on the pedestal and core confinement properties are examined. At the identical plasma configuration between the discharges with and without FST, the pedestal temperature in case with FST can be raised by ∼20-25% compared to the case without FST at a given pedestal density. Larger type-I ELM spikes appear due to the increase in the pedestal pressure in case with FST. The ELM frequency normalized by the power crossing the sepratrix becomes relatively lower at a given line-averaged electron density. At a given absorbed power and pedestal density, the ion temperature profile becomes higher by ∼20% over the whole range of plasma core in case with FST. The stored energy also becomes larger by ∼20%. The ion temperature gradient in the ETB region becomes steeper by ∼5% and the pedestal width becomes wider by ∼10% with decreasing the fast ion loss fraction by ∼20%. After the FST installation, the toroidal rotation profile is shifted to the co-direction over the whole radial range including the plasma edge. The energy confinement can be improved as the fast ion loss fraction decreases. However, the toroidal rotation shifts to the co-direction monotonically together with the reduction of the fast ion loss. Since the radial electric field is influenced by the fast ion loss and toroidal rotation, the role of the toroidal rotation on the pedestal structure distinguished from that of fast ion loss should be analyzed in the next step study. (author)