Macroscopic trends of linear tearing stability in cylindrical current profiles

The likelihood of realising tokamak power-plants will be greatly improved by the discovery of high-gain equilibria that resist the formation of small islands and hence avoid the disruptive neoclassical tearing mode. However the complexity and variety of tearing-onset physics has obscured the design decisions that may lead to such stability. Here we investigate the variation that current profiles can bring about in preventing tearing onset through the cylindrical linear tearing stability parameter ∆′. A database of 159148 realistic pilot-plant current profiles was generated with Monte Carlo sampling, and the distribution of ∆′ values was linked with interpretable profile characteristics. In agreement with prior theoretical and experimental studies, ∆′ was found to be strongly correlated with the existence and steepness of a local toroidal current well or hill, with the former destabilising and the latter stabilising. In the absence of these two cases, the remaining ∆′ values were linearly bounded by the toroidal current gradient at the rational surface.

发现能抑制小磁岛形成、从而避免破坏性新经典撕裂模（neoclassical tearing mode）的高增益平衡态，将大幅提升托卡马克（tokamak）发电站的实现可能性。然而，撕裂模触发物理机制的复杂性与多样性，使得可能实现这种稳定性的设计决策变得模糊不清。本文通过圆柱线性撕裂模稳定性参数∆′，研究电流剖面在抑制撕裂模触发方面所能产生的变化。通过蒙特卡洛采样（Monte Carlo sampling）生成了包含159148个真实试点电站电流剖面的数据库，并将∆′值的分布与可解释的剖面特征关联起来。与先前的理论和实验研究一致，研究发现∆′与局部环向电流阱或电流峰的存在及其陡峭程度密切相关——前者会导致失稳，后者则具有稳定作用。