The enhanced transport of trapped energetic ions (TEIs) in the presence of resonant interactions between trapped fast ions and a rotating magnetic island is investigated within a drift-kinetic framework. Gyro-orbit banana center model equations of resonances between the island rotation, the bounce motion of trapped fast ions, and their precession frequency (poloidal precession and precession in the helical direction) are constructed. There are two solutions for resonances in phase space for different mode numbers, with only one solution having low-energy resonant lines (<100 keV); the other has not only low-energy resonant lines but also high-energy lines (≥100 keV). Island rotation plays an important role in the low-energy region, especially near the trapped-passing boundary. The precession frequency is more important when resonances occur in the high-energy area. Thus, the effect of islands on TEI transport in a low-energy region is the focus of this paper. Transport fluxes caused by collisions, resonances, and symmetry breaking induced by an island are obtained. We divide transport fluxes into two types: Γc arising from magnetic drift and Γb arising from the island rotation. There is a discontinuity in Γc with different island widths near the island separatrix. On the right-hand side of the (m = 2, n = 1) rational surface, Γc is more important than Γb, and at the plasma boundary, the flux due to drift can suppress Γb, which makes fast ions move toward inner plasma. On the left-hand side of the rational surface, Γb is dominant. When the island width is larger than a certain threshold, the fluxes oscillate, and Γb is far larger than Γc.
The mismatch of the operating parameters of the NBI ion source of the nuclear fusion experimental device will lead to the instability of the plasma, and maybe cause breakdown in the ion source, which will limit the operation of the NBI long pulse and high power. To stabilize the plasma in the NBI ion source, data from multiple rounds of experiments along with a priori information obtained from a predictive plasma model are used. For the problem of low accuracy of the existing key-values extraction algorithms for experimental data, the OPTICS (Ordering Point To Identify the Cluster Structure) algorithm is used to improve the accuracy of the experimental data extraction, and provide a reference for the failure analysis during the experimental operation. A method based on self-organizing feature map (SOM) and BP neural network is adopted. By training historical data, the pulse width of the NBI ion source beam extraction process is estimated under given parameters to adjust the operating parameters.
Water- cooled ceramic breeder (WCCB) blanket is one of the candidate blanket for China Fusion Engineering Test Reactor (CFETR) independently developed by China Institute of plasma physics. The first wall (FW) is a component of WCCB, which directly faces the plasma. FW contains flow channels and has complex shape structure, therefore, it is difficult to complete the full-scale manufacturing by one kind of welding process. Hence, in the development process, the components of FW are first connected by hot isostatic pressing (HIP), and then connected by electron beam welding (EBW), so as to form the full-scaled FW connection. In this paper, the EBW process of FW was studied. The results showed that when the electron beam current was 50 mA and the focus was on the surface, the welded joint with 20 mm penetration and good shape can be formed. After the one time welding and the twice welding (overlapping first welding) of the weld, the tensile test fracture occurred in the base metal. The impact energy of the one time welding was 13 MPa, 18 MPa, and 21 MPa, respectively, and the impact energy of the twice welding was 19 MPa, 20 MPa, and 51 MPa, respectively. The microstructure of the joint was composed of delta-ferrite and lath martensite. When the weld penetration was increased to 50 mm, the lower the focus is, the smaller the porosity at the bottom of the weld is. Similarly, when the lower focus was used, the porosity at the bottom of the weld disappeared basically; The EBW test on the scaled FW with W/Cu sheets showed that when the we took the test pieces with the W-Cu sheet spacing is 4 mm, the welded joint with good surface shape and no internal defects can be formed without scanning deflection electron beam welding, and ultrasonic testing showed that EBW does not affect on the HIP interface. This provides a favorable basis for the future test of equal ratio FW test piece and the welding of actual FW.
在HL-2A装置等离子体放电参数下,模拟研究了局部反磁剪切位形时(存在具有同一安全因子值的多个有理面时)高能量粒子(EP)激发的 m/n=2/1 的高能量粒子模(EPM),并给出了含有 EP 驱动和环耦合效应的m/n>1 模式的本征值方程.通过数值求解本征值方程,计算了径向模结构,并模拟了 EPM 增长率和模频率对于EP比压(βh)的依赖关系.计算结果表明,局部反磁剪切位形下捕获EP可以驱动全域的EPM不稳定性,其特征类似于m/n=2/1 类鱼骨模,这为相关实验提供了理论解释.通过研究EP参数对模式的影响,发现随着粒子径向分布的平化,模式趋于稳定;当束注入能量增加时,强的阿尔芬连续谱阻尼将导致不稳定性增长率的减小.
利用托卡马克集成模拟与实验分析平台(OMFIT)开展了HL-3 装置ECCD驱动效率的研究,分析了ECCD系统发射天线在等离子体环向与极向所成的角度、等离子体密度、电子温度和磁场对驱动电流大小和位置的影响.研究发现,环向角和极向角范围分别为185°～200°、85°～105°时,ECCD电流驱动效率比较高,驱动电流可以覆盖到归一化半径0.4～0.6.研究还发现,电子温度显著影响ECCD电流驱动效率,温度越高驱动电流越大;在弱场侧磁场强度(1.9～2.2T)越小,驱动电流分布归一化半径越小和驱动电流越大.
