托卡马克程序Gysela中的真实几何目标
Targeting realistic geometry in Tokamak code Gysela
摘要：
在用于托卡马克的磁约束等离子体中，湍流是限制这类反应堆性能的特定输运的原因。陀螺运动模拟能够捕获引起热损失的离子和电子湍流，但也需要最先进的HPC技术来处理计算成本。这种模拟是一个重要的工具，以建立良好的运行制度，在托卡马克，如ITER，这是目前正在建设。陀螺动力学仿真的一些关键问题是：高效和鲁棒的数值格式，精确的几何描述，良好的并行算法。这项工作的框架是半拉格朗日设置为解决陀螺Vlasov方程和Gyseka代码。本文提出了一种新的插值方法，它可以处理极向平面中r=0处的网格奇异性（极坐标系用于Gysela中的矩）。为了节省内存和计算量，提出了极向面非均匀网格划分方法。为了处理非均匀网格，对插值方法、gyroaverage算子和Poisson求解器进行了修正。建立从极坐标到更真实的等离子体形状的双射的映射被用来提高真实性。收敛性研究，以建立我们的新方法的有效性和鲁棒性。
英文摘要：
In magnetically confined plasmas used in Tokamak, turbulence is responsible for specific transport that limits the performance of this kind of reactors. Gyrokinetic simulations are able to capture ion and electron turbulence that give rise to heat losses, but require also state-of-the-art HPC techniques to handle computation costs. Such simulations are a major tool to establish good operating regime in Tokamak such as ITER, which is currently being built. Some of the key issues to address more realistic gyrokinetic simulations are: efficient and robust numerical schemes, accurate geometric description, good parallelization algorithms. The framework of this work is the Semi-Lagrangian setting for solving the gyrokinetic Vlasov equation and the Gyseka code. In this paper, a new variant for the interpolation method is proposed that can handle the mesh singularity in the poloidal plane at r=0 (polar system is used for the moment in Gysela). A non-uniform meshing of the poloidal plane is proposed instead of uniform one in order to save memory and computations. The interpolation method, the gyroaverage operator, and the Poisson solver are revised in order to cope with non-uniform meshes. A mapping that establish a bijection from polar coordinates to more realistic plasma shape is used to improve realism. Convergence studies are provided to establish the validity and robustness of our new approach.
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