Experimental Investigation Of Metallic Impurity Behavior In High-confinement Regime On EAST Tokamak

The accumulation of high-Z impurities in the core plasma must be controlled in high performance, steady-state and long-pulse operation of future fusion. The accumulation of high-Z impurities can lead to dilution of the fusion fuel and enhance radiation power loss, and always deteriorates the confinement or terminates the H-mode probably. This is a serious issue for magnetized plasmas, especially in machines with tungsten (W) divertor plates, where the strike points can inject W into the plasma.Plentiful diagnostics which can give more information of impurities behavior on EAST are introduced. Mainly introduces the development of extreme ultraviolet (EUV)spectrometers (EUV Long / EUV Short / EUV_Long2) on EAST,which are important diagnostic for investigation of impurities transport in core plasma due to their measurement of higher ionization of impurities. Besides, the newly developed Filterscope and OSMA spectrometers which work in visible range, can give the information of impurities source in the plasma edge, visible bremsstrahlung measurement is used to calculate Zeffwhich reveals the impurity level of the plasma,bolometer and soft X-ray arrays are used to measure the total radiation power of the plasma. Based on these diagnostics, the related impurity behavior studies have been carried out, which would be helpful to understand the impurity transport mechanisms in order to find an effective method to prevent impurity accumulation and maintain high performance, steady-state and long-pulse operation.The investigation of tungsten (W) behavior in NBI dominated heating H-mode is carried out on EAST. The W induced by NBI injection and the W accumulation in H-mode phase are always observed, thus result in a degradation of confinement and a serious effect on profile of parameters. It is also found the W density decreased with the radio-frequency (RF) power ratio and the frequency of ELMs. The W accumulation is prevented in the ELMy H-mode which with neoclassical tearing mode (NTM), but the confinement of plasma is also limited. However, in the ELMy H-mode which with edge density fluctuation (EDF), the W accumulation can be effectively controlled as well as the wonderful confinement is obtained in this regime. Then, the investigation of intergrated small ELM (ISE) H-mode regime shows a major advantage of an L-mode W confinement time and density exhibited simultaneously with normal H-mode energy confinement. These analysis show a strong dependence of impurity transport on factor of fatety (q95) and total heating power. Finally, in the low q95 discharges, the W density controlled by using the n=1 RMP coils when phase difference is more than 180° is observed.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 42IP0.32Bt0.2ne-0.43Ptotal-0.4 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.