The ubiquitous sawtooth phenomena in tokamaks are so named because the central temperature rises slowly and falls rapidly, similar to the blades of a saw. First discovered in 1974, it has so far eluded a theoretical explanation that is widely accepted and consistent with experimental observations. We propose here a new theory for the sawtooth phenomena in auxiliary heated tokamaks, which is motivated by our recent understanding of “magnetic flux pumping.” In this theory, the role of the ( m , n ) = ( 1 , 1 ) mode is to generate a dynamo voltage, which keeps the central safety factor, q0, just above 1.0 with low central magnetic shear. When central heating is present, the temperature on axis will increase until at some point, and the configuration abruptly becomes unstable to ideal MHD interchange modes with equal poloidal and toroidal mode numbers, m = n > 1. It is these higher order modes and the localized magnetic stochasticity they produce that cause the sudden crash of the temperature profile, not magnetic reconnection. Long time 3D MHD simulations demonstrate these phenomena, which appear to be consistent with many experimental observations.

中文翻译：

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托卡马克锯齿现象的新解释

托卡马克中无处不在的锯齿现象之所以如此命名，是因为中心温度上升缓慢，下降迅速，类似于锯子的刀片。它于 1974 年首次被发现，迄今为止，它没有得到一个被广泛接受并与实验观察一致的理论解释。我们在此针对辅助加热托卡马克中的锯齿现象提出了一种新理论，该理论受到我们最近对“磁通泵浦”的理解的启发。在该理论中，( m , n ) = ( 1 , 1 ) 模式的作用是产生发电机电压，使中心安全系数 q0 保持在 1.0 以上且中心磁切变低。当存在集中供热时，轴上的温度将增加直到某个点，并且配置突然变得不稳定，以具有相等的极向和环形模式数的理想 MHD 交换模式，m = n > 1。正是这些高阶模式和它们产生的局部磁随机性导致了温度分布的突然崩溃，而不是磁重联。长时间的 3D MHD 模拟证明了这些现象，这似乎与许多实验观察一致。