Search

A significant change in the background ELM behavior prior to neon (Ne) seeding has been observed in a series of repetitive radiative divertor experiments in EAST. With similar operational parameters, the ELM behavior before Ne seeding changes from large to mixed ELMs, and finally evolves to pure small ELMs. Meanwhile, a significant increase in both Ne and high-Z impurity (W and Mo) emissions has been observed in the bulk plasma, suggesting the retention and recycling of Ne impurity from the wall surface. Experimental results show that the variation in background ELM behavior is highly correlated with the occurrence of high-Z impurity accumulation. The increased accumulation of high-Z impurities leads to a lower electron temperature both in the plasma core and edge, accompanied by a higher and more peaked electron density in the plasma core. Pedestal linear stability analysis reveals that the decreased pedestal electron temperature and thus the lower pressure gradient and lower edge current density are the primary reason for the change of background ELM behavior. The concentration of recycling Ne in the bulk plasma is estimated to be ∼1% in the discharges with pure small ELMs.

In this paper, we present experimental studies of both high-kr ( cm−1, and , respectively; ) and high- ( cm−1, and , respectively; ) turbulence behavior during an ohmic energy confinement degradation phase in experimental advanced superconducting tokamak (EAST). High-kr turbulence from density fluctuation at and high- turbulence from density fluctuation at –0.97 were measured by tangential and poloidal CO2 laser collective scattering diagnostics, respectively. Note that kr, , and are radial wavenumber, poloidal wavenumber, perpendicular wavenumber and ion gyroradius at electron temperature, respectively. Both high-kr/ turbulence power and energy confinement time are found to be temporally correlated to line-averaged electron density ne in the plasma current flat-top phase (Ip  =  0.4 MA): when the ne shows continuous increase/decrease, the high-kr/ turbulence power increases/decreases correspondingly and the shows corresponding decrease/increase; the stable ne is related to stable both and high-kr/ turbulence power. Statistical results of high-kr/ turbulence power versus further imply that high-kr/ turbulence shows a strong correlation with plasma energy confinement degradation in high line-averaged ne condition, but high-kr and high- turbulence have relatively weak and no dependence on the transition between linear range in low-ne condition and energy confinement degradation in the high-ne condition, respectively. Moreover, profiles of electron temperature Te and ne as well as their normalized gradients in a part of high- density fluctuation measurement region also have been given to qualitatively explain the enhancement of turbulence power with the increase of line-averaged ne. [ABSTRACT FROM AUTHOR]

As the testing mockup of tritium breeding blanket for DEMO, the Chinese helium cooled ceramic breeder test blanket system (HCCB TBS) is under development by China and will be tested in ITER to verify key tritium breeding blanket technologies. After the approval of the conceptual design of the HCCB TBS by the ITER Organization in 2015, the design optimization and more research and development activities for the HCCB TBS have begun for the preliminary design. This paper gives an overview of the recent progress of the HCCB TBS development in China, including the design optimizations, material development, mockup fabrication and test facility construction. [ABSTRACT FROM AUTHOR]

The snake perturbations around q  =  2 surface with strong poloidal asymmetry are frequently observed on EAST after the injection of high-Z impurities. A new pair of Beta-induced Alfvén eigenmodes (BAEs) with lower frequencies also come along with the 2/1 snake fluctuations, in addition to the conventional BAE pair that accompany the pure 2/1 tearing modes (TMs) on EAST, which have already been investigated (Xu et al 2013 Plasma Phys. Control. Fusion55 065002). The radial structures of the intensities of the snake perturbations and the two BAE pairs are mapped out for the first time, indicating that these BAE quartet are discrete modes over the radial extension and are situated slightly outside the annulus of TM activities but centered at slightly different positions. The constant frequency spectra of the BAEs are explained as the eigen-solutions of the radial differential equation for the global modes, and the rich multiplicity of BAEs is attributed to various levels of BAE continuum splittings when more detailed physics are taken into consideration. [ABSTRACT FROM AUTHOR]

The transient perturbation method with metallic impurities such as iron (Fe, Z  =  26) and copper (Cu, Z  =  29) induced in plasma-material interaction (PMI) procedure is used to investigate the impurity confinement characters in lower hybrid wave (LHW) heated EAST sawtooth-free plasma. The dependence of metallic impurities confinement time on plasma parameters (e.g. plasma current, toroidal magnetic field, electron density and heating power) are investigated in ohmic and LHW heated plasma. It is shown that LHW heating plays an important role in the reduction of the impurity confinement time in L-mode discharges on EAST. The impurity confinement time scaling is given as on EAST, which is close to the observed scaling on Tore Supra and JET. Furthermore, the LHW heated high-enhanced-recycling (HER) H-mode discharges with ~25 kHz edge coherent modes (ECM), which have lower impurity confinement time and higher energy confinement time, provide promising candidates for high performance and steady state operation on EAST. [ABSTRACT FROM AUTHOR]