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中国物理学会期刊

中国聚变工程试验堆上新经典撕裂模和纵场波纹扰动叠加效应对alpha粒子损失影响的数值模拟

CSTR: 32037.14.aps.70.20201972

Numerical simulation of synergistic effect of neoclassical tearing mode and toroidal field ripple on alpha particle loss in China Fusion Engineering Testing Reactor

CSTR: 32037.14.aps.70.20201972
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  • 托卡马克聚变堆中高能量alpha粒子的良好约束是获得稳态燃烧等离子体的前提, 除了磁场波纹损失, 不稳定性也会引起额外的损失. 本文基于中国聚变工程试验堆(CFETR)参数, alpha粒子初始分布和新经典撕裂模(NTM)扰动分布, 利用粒子导心跟踪方法分别对磁场波纹和NTM两种扰动及叠加下的粒子损失进行了详细的数值模拟. 结果显示粒子损失份额不随NTM扰动幅度增大而增大, 两种扰动的叠加效应不明显. 通过扫描装置波纹度大小以及分析相空间粒子密度和波纹损失区分布, 确认原因是CFETR波纹损失区较小, 没有覆盖高能量粒子(EP)密度和NTM扰动主要分布区. 此外, NTM没有引起直接粒子损失和俘获粒子剖面坍塌. 显著的俘获粒子密度剖面展平, 并扩展到波纹损失区是两种扰动叠加效应显著的前提. 无碰撞波纹随机扩散是CFETR初始分布alpha粒子的主要损失通道, 通行粒子约束不受磁场波纹影响. 本文研究结果对CFETR概念设计中alpha粒子物理和低频不稳定性下的EP行为具有重要意义.

     

    Confinement of fusion born alpha particles in tokamak is the key issue to burning plasma. Apart from toroidal field ripple, instabilities can induce energetic particles to lose and be redistributed. Based on the parameters of China Fusion Engineering Testing Reactor (CFETT) hybrid scenario, alpha particle distribution and neoclassical tearing mode structure, the alpha particle loss induced under perturbation of ripple and neoclassical tearing mode (NTM) is calculated with the guiding center code ORBIT. The inputs have the initial distribution of alpha particles which is obtained with the TRANSP/NUBEAM code, the static NTM perturbation with different amplitudes which is obtained from TM1 code, and the ripple field from engineering design. The results show that the heat load on last closed flux surface is about 0.1 MW/m2, with ripple and collision included. The collisionless stochastic ripple diffusion is the main loss channel of initial alpha particle distribution in the CFETR, and the ripple perturbation has no influence on passing particles. The loss fraction does not increase with the NTM perturbation amplitude increasing, the synergistic effect is negligible. The scanning of ripple amplitude shows that the synergistic effect is slight. The monoenergetic initial distribution of alpha particles can give different types of orbits in the plane of ( P_\zeta ,\mu ), such as the domains of trapped particle and passing particle, lost particle and confined particle. The trapped fraction of initial alpha particles is about 27%, ripple loss region in phase space is narrow and away from the main trapped particle distribution. The increasing of ripple perturbation in simulation does enlarge the ripple loss domain in the phase space ( P_\zeta ,\mu ), which is corresponding to a lager ripple loss fraction and has more trapped-passing boundaries. The NTM perturbation does enlarge the orbit excursions of trapped particles, and thus increasing the trapped passing transition near the boundary. The slight synergistic effect in calculation with larger ripple amplitude is explained by ripple loss region having more trapped-passing boundaries, not by the profile flattening of trapped particles. The NTM perturbation and finite collision can transit the passing particle to trapped particle near the boundary. With the help of kinetic Poincare plot, neither direct particle loss nor profile flattening of trapped particles is observed. The loss fraction enhancement can happen only when the profile flattening of trapped particles takes place within the ripple loss region, which is not the case in CFETR. The conclusion of this work contributes a lot to the design of CFETR and the study of alpha particle physics.

     

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