Study Of Divertor Plasma Physics And Impurity Injection Behavior On EAST

Nuclear fusion has the potential to provide a major part of mankind’s energy needs for many millennia in the future. The divertor is one of the key components of modern tokamak, the main function of the divertor system is to minimize the impurity content in the plasma as well as to exhaust part of the plasma thermal power. The divertor which was proposed at the beginning of magnetic fusion research also plays an important role in fusion research now.The ’two-point’ model is a simple one-dimensional model of plasma edge physics for tokamak. The principle of divertor detachment, plasma drifts and divertor asymmetry are important contents of divertor plasma research. Some divertor diagnostics on Experimental Advanced Superconducting Tokamak (EAST) are described, such as divertor Langmuir probe, Da radiation arrays, CIII radiation arrays, bremsstrahlung and infrared camera.The first dedicated divertor physics experiments were focused on ohmic plasma discharges. The behavior of divertor plasma, divertor asymmetry, and different fueling methods were investigated in both single null (SN) and double null (DN) divertor discharges. Divertor plasma detachment was achieved for the first time on EAST, by ramping up the density during the discharge with well controlled, steady divertor configuration. Dome gas fueling is more efficient than inner or outer target for SN and DN. Particle and heat fluxes are higher at the outer target plate for both SN and DN, the DN divertor operation exhibits much stronger in-out asymmetry favoring the outer divertor targets. DN divertor configuration also leads an up-down asymmetry with higher particles to the divertor which is in the ion VB drift direction.The preliminary radiative divertor experiments have conducted by injecting D2and its mixture with Ar (D2+5.7%Ar) with active divertor pumping for SN and DN in ohmic discharges. D2and Ar puffing promotes complete detachment or partial detachment near the strike points, greatly reducing the peak heat fluxes at the targets (over50%), hence improving the in-out divertor asymmetry, while the far-SOL plasma of the outer divertor remains attached in some discharges. However, the injected gas was not well confined inside the outer divertor with some leakage into the inner divertor, thus reducing further the heat fluxes to the inner target, accelerating the detachment of the inner target plate. The radiative divertor experiments have also explored under low (L) and high (H)-mode comfinement regime in EAST, with Ar and its mixture (D2+25%Ar). The Ar injection has greatly reduced particle and heat fluxes to the divertor in L-mode discharges, achieving nearly complete detached divertor plasma regime for SN and DN, without increasing the core impurity content. The results from Ar seeding in H-modes demonstrating a significant increase in the frequency and decrease in the amplitude of the edge localized modes (ELMs), thus reducing both particle and heat loads caused by the ELMs. Radiative divertor experiments explored an effective way of high power long pulse operation for EAST.Modelling studies of SOL-divertor plasma are carried out using the edge plasma code package B2.5/Eirene-SOLPS5.0. The modelling results of divertor detachment are consistent with the experimental results except the ion saturation current to the outer target is much smaller than experimental measurement. Modeling results of Ar and Ne injection shows Ar seeding is more effective for controlling the divertor power fluxes.