动态情形下Dreicer逃逸电子产生模型的有效性
Validity of models for Dreicer generation of runaway electrons in dynamic scenarios
摘要：
逃逸电子建模工作的动机是这些高能粒子对大型聚变装置造成的风险。复杂的动力学模型可以捕获逃逸电子产生的大部分特征，但具有高的计算成本，这可以通过使用计算上更便宜的简化动力学代码来避免。在本文中，我们比较了减少动力学和动力学模型，以确定当前求解器，假设准平稳的分析计算的基础上，可以使用。德莱塞生成率是由两个不同的求解器在欧洲集成建模框架中开发的工作流程中并行计算的，这是通过计算尚未集成到框架中的第三个代码来补充的。Runaway Fluid是一个简化的动力学程序，NORSE是一个使用非线性碰撞算子的动力学程序，DREAM是一个线性化的Fokker-Planck解算器，用于研究跨越整个托卡马克相关范围的不同等离子体场景中电场动态变化的影响。我们发现，在时间尺度短于或相当于电子碰撞时间在临界速度逃逸电子产生动力学效应没有捕获的减少动力学模型发挥了重要作用。这种特征时间尺度很容易计算，并且可以可靠地用于确定是否需要动力学建模，或者预计更便宜的简化动力学代码可以提供足够准确的结果。这个标准可以自动化，因此，它可以是非常有益的全面的自洽建模框架，试图模拟复杂的事件，如托卡马克启动或中断。
英文摘要：
Runaway electron modelling efforts are motivated by the risk these energetic particles pose to large fusion devices. The sophisticated kinetic models can capture most features of the runaway electron generation but have high computational costs which can be avoided by using computationally cheaper reduced kinetic codes. In this paper, we compare the reduced kinetic and kinetic models to determine when the former solvers, based on analytical calculations assuming quasi-stationarity, can be used. The Dreicer generation rate is calculated by two different solvers in parallel in a workflow developed in the European Integrated Modelling framework, and this is complemented by calculations of a third code that is not yet integrated into the framework. Runaway Fluid, a reduced kinetic code, NORSE, a kinetic code using non-linear collision operator, and DREAM, a linearized Fokker-Planck solver, are used to investigate the effect of a dynamic change in the electric field for different plasma scenarios spanning across the whole tokamak-relevant range. We find that on time scales shorter than or comparable to the electron collision time at the critical velocity for runaway electron generation kinetic effects not captured by reduced kinetic models play an important role. This characteristic time scale is easy to calculate and can reliably be used to determine whether there is a need for kinetic modelling, or cheaper reduced kinetic codes are expected to deliver sufficiently accurate results. This criterion can be automated, and thus it can be of great benefit for the comprehensive self-consistent modelling frameworks that are attempting to simulate complex events such as tokamak start-up or disruptions.
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