Impurity temperature screening is a favourable neoclassical phenomenon involving an outward radial flux of impurity ions from the core of fusion devices. Quasisymmetric magnetic fields lead to intrinsically ambipolar neoclassical fluxes that give rise to temperature screening for low enough $\unicode[STIX]{x1D702}^{-1}\equiv d\ln n/d\ln T$ . In contrast, neoclassical fluxes in generic stellarators will depend on the radial electric field, which is predicted to be inward for ion-root plasmas, potentially leading to impurity accumulation. Here, we examine the impurity particle flux in a number of approximately quasisymmetric stellarator configurations and parameter regimes while varying the amount of symmetry breaking in the magnetic field. For the majority of this work, neoclassical fluxes have been obtained using the SFINCS drift-kinetic equation solver with electrostatic potential $\unicode[STIX]{x1D6F7}=\unicode[STIX]{x1D6F7}(r)$ , where $r$ is a flux-surface label. Results indicate that achieving temperature screening is possible, but unlikely, at low-collisionality reactor-relevant conditions in the core. Thus, the small departures from symmetry in nominally quasisymmetric stellarators are large enough to significantly alter the neoclassical impurity transport. A further look at the magnitude of these fluxes when compared to a gyro-Bohm turbulence estimate suggests that neoclassical fluxes are small in configurations optimized for quasisymmetry when compared to turbulent fluxes.

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接近准对称的仿星器中的杂质温度筛选

杂质温度筛选是一种有利的新古典现象，涉及来自聚变装置核心的杂质离子向外径向流动。准对称磁场导致本质上的双极新古典通量，从而产生足够低的温度筛选 $\unicode[STIX]{x1D702}^{-1}\equiv d\ln n/d\ln T$ . 相比之下，通用仿星器中的新古典通量将取决于径向电场，预计离子根等离子体向内，可能导致杂质积累。在这里，我们检查了许多近似准对称的仿星器配置和参数方案中的杂质粒子通量，同时改变了磁场中对称破缺的数量。对于这项工作的大部分，使用具有静电势的 SFINCS 漂移动力学方程求解器获得了新古典通量 $\unicode[STIX]{x1D6F7}=\unicode[STIX]{x1D6F7}(r)$ ， 在哪里 $r$ 是通量表面标签。结果表明，在堆芯的低碰撞反应堆相关条件下，实现温度筛选是可能的，但不太可能。因此，在名义上的准对称仿星器中，与对称性的微小偏差足以显着改变新古典杂质传输。与陀螺-玻姆湍流估计相比，进一步观察这些通量的大小表明，与湍流相比，新古典通量在针对准对称优化的配置中很小。