Favourable scenarios established by SMBI for the realization of the ELMy H-mode at HL-2A

The ELMy H-mode plasmas realized with the supersonic molecular beam injection(SMBI) are studied in relation to the energy confinement and the heating power for the L–H transition(P_(L-H) ) in the HL-2A tokamak. A database is assembled for this study based on the ELMy H-mode discharges during the experimental campaigns in the period 2009–2013at the HL-2A tokamak. The statistical results show that the SMBI is favourable for reaching the H-mode by reducing the heating power at the L–H transition and for the H-mode performance by improving the energy confinement compared with the ordinary gas puffing(GP). The reduction of P_(L-H) is about 20% when the density is low, and the energy confinement enhancement factor of H_(H98y2)= τ_E/τ_(th,98y2) ≈ 1.5 is achieved with the SMBI. Note that in the database the density dependence of P_(L-H) is non-monotonic with the ˉne,min≈ 3×10~(19) m~(-3) at which the P_(L-H) is minimum. Most of P_(L-H) data are on the low density branch where the P_(L-H) increases with the decrease in density. The minimum of the P_(L-H) in HL-2A is comparable to the ITPA multi-machine threshold power scaling P_(thr■scal08). The physics behind the reduction of the P_(L-H) with the SMBI is also investigated in relation to the change of the density gradient at the plasma edge, the gas fuelling efficiency, and the recycling.     

Experimental and modeling researches of dust particles in the HL-2A tokamak

The investigation of dust particle characteristics in fusion devices has become more and more imperative.In the HL-2A tokamak,the morphologies and compositions of dust particles are analyzed by using scanning electron microscopy(SEM) and energy dispersive x-ray spectroscopy(EDX) with mapping.The results indicate that the sizes of dust particles are in a range from 1 μm to 1 mm.Surprisingly,stainless steel spheres with a diameter of 2.5μm-30 μm are obtained.The production mechanisms of dust particles include flaking,disintegration,agglomeration,and arcing.In addition,dynamic characteristics of the flaking dust particles are observed by a CMOS fast framing camera and simulated by a computer program.Both of the results display that the ion friction force is dominant in the toroidal direction,while the centrifugal force is crucial in the radial direction.Therefore,the visible dust particles are accelerated toriodally by the ion friction force and migrated radially by the centrifugal force.The averaged velocity of the grain is on the order of~100 m/s.These results provide an additional supplement for one of critical plasma-wall interaction(PWI) issues in the framework of the International Thermonuclear Experimental Reactor(ITER) programme.     

HL-2M装置中性束注入加热系统研制进展

为开展磁约束堆芯燃烧等离子体物理实验,正在建造的HL-2M装置拟建造3条5 MW的中性束注入加热束线。简要概述了HL-2M装置NBI加热系统的总体规划,第1条5MW-NBI加热束线的设计,离子源调试实验,注入器核心部件的安装和测试结果。通过调试,目前单个离子源引出束流达到36 A,加速电压75 kV,离子束功率达到2.4 MW,脉冲宽度3 s。通过测试发现：注入器的4条离子束汇聚角误差小于±0.1°,残留离子偏转磁体的磁场测试值与模拟计算值偏差小于±5%,注入器静态真空值达到1.0×10^-3 Pa。注入器采用大型非标低温泵,低温泵的抽速达到2.40×10⁶ L/s。第1条5MW-NBI加热束线的试装和测试结果表明,该束线能够满足HL-2M装置NBI加热的技术要求。     

Study of runaway electron behaviour during electron cyclotron resonance heating in the HL-2A Tokamak

During the current flat-top phase of electron cyclotron resonance heating discharges in the HL-2A Tokamak, the behaviour of runaway electrons has been studied by means of hard x-ray detectors and neutron diagnostics. During electron cyclotron resonance heating, it can be found that both hard x-ray radiation intensity and neutron emission flux fall rapidly to a very low level, which suggests that runaway electrons have been suppressed by electron cyclotron resonance heating. From the set of discharges studied in the present experiments, it has also been observed that the efficiency of runaway suppression by electron cyclotron resonance heating was apparently affected by two factors: electron cyclotron resonance heating power and duration. These results have been analysed by using a test particle model. The decrease of the toroidal electric field due to electron cyclotron resonance heating results in a rapid fall in the runaway electron energy that may lead to a suppression of runaway electrons. During electron cyclotron resonance heating with different powers and durations, the runaway electrons will experience different slowing down processes. These different decay processes are the major cause for influencing the efficiency of runaway suppression. This result is related to the safe operation of the Tokamak and may bring an effective control of runaway electrons.     

HL-2M等离子体对共振磁扰动线圈电流相位响应的模拟

在HL-2M托卡马克平衡位形(Ip=1.0MA,βN=1.62,q95=4.01)下,使用环形单流体程序MARS-F研究了等离子体对共振磁扰动(RMP)线圈电流相位差的响应.在最优相位差时,扰动磁场显著地改变边界层磁场的拓扑,形成明显的磁岛链,增加了等离子体在边界层的输运,降低了压强梯度,减小了对ELM的驱动.模拟结果...