One of the key aspects when simulating the plasma edge is the treatment of the neutral particles. Neutral particles can be described by a kinetic equation, which is difficult to solve due to the high dimensionality of the phase space and the high collisionality between the neutral particles and the plasma background, especially in the (partially) detached regimes anticipated for future reactors. We consider a recently proposed hybrid fluid-kinetic method that is based on a micro–macro decomposition of the kinetic equation and mitigates the problems related to both the high dimensionality and the high collisionality. However, this method is prone to cancellation errors due to the introduction of particles with both positive and negative weights. In each iteration of the method, the particles undergo a weight projection step, which we identify as the main source of cancellation errors. We use techniques from numerical linear algebra for solving ill-conditioned linear systems to improve the numerical stability of the weight projection step and reduce the cancellation errors. The reduction of cancellation errors allows for further speedup in the hybrid fluid-kinetic method.

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关于在解决描述等离子体边缘中性物质的动力学方程的混合流体动力学方法中消除误差的缓解

模拟等离子体边缘的关键方面之一是中性粒子的处理。中性粒子可以用动力学方程来描述，由于相空间的高维以及中性粒子与等离子体背景之间的高碰撞性，这很难求解，特别是在未来反应堆预期的（部分）分离状态中。我们考虑了一种最近提出的混合流体动力学方法，该方法基于动力学方程的微观-宏观分解，并减轻了与高维和高碰撞性相关的问题。然而，由于引入了具有正负权重的粒子，这种方法容易产生抵消错误。在该方法的每次迭代中，粒子都会经历一个权重投影步骤，我们认为这是取消错误的主要来源。我们使用数值线性代数的技术来求解病态线性系统，以提高权重投影步骤的数值稳定性并减少抵消误差。消除误差的减少允许进一步加速混合流体动力学方法。