发表机构
University of Wisconsin–Madison; University of Greifswald（威斯康星大学麦迪逊分校; 格赖夫斯瓦尔德大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究首次全面分析EMC3-EIRENE在HSX仿星器中的数值误差，发现常用度量低估统计误差，并提出了改进精度与效率的最佳实践。
AI 中文摘要
使用EMC3-EIRENE等代码进行的等离子体边缘模拟被广泛用于研究聚变磁约束装置。然而，数值误差可能显著影响模拟解，且往往未被充分表征。这些误差包括由蒙特卡洛粒子的有限采样和追踪导致的统计误差、偏差和时间积分误差，以及由有限网格分辨率导致的离散化误差。本工作首次对仿星器几何中EMC3-EIRENE模拟进行了全面的数值误差分析，重点关注螺旋对称实验装置（HSX）中的边缘等离子体。分析了基本的等离子体和中性粒子量，并将误差降低速率与理论预期进行了比较。统计误差、偏差和时间积分误差已被完全表征；然而，由于EMC3-EIRENE中使用的复杂网格几何，离散化误差的量化仍然具有挑战性。常用的体积平均相对变化度量被证明会系统性地低估统计误差，这凸显了EMC3-EIRENE分析中的一个关键缺陷，即在模拟解中仍存在显著噪声的情况下却声称收敛。与托卡马克模拟相比，仿星器模拟中时间积分误差的主要贡献被证明有所不同，这与两种装置之间横越场输运的相对重要性有关。基于这些结果和现有文献，我们建立了在通用仿星器建模中提高EMC3-EIRENE精度和效率的最佳实践。
英文摘要
Plasma edge simulations with codes like EMC3-EIRENE are widely used to study fusion magnetic confinement devices. However, numerical errors can significantly impact the simulation solution and are often insufficiently characterized. These errors consist of the statistical error, bias, and time integration error, resulting from the finite sampling and tracking of Monte Carlo particles, and the discretization error, resulting from a finite grid resolution. This work presents the first comprehensive numerical error analysis of EMC3-EIRENE simulations in stellarator geometries, focusing on edge plasmas in the Helically Symmetric eXperiment (HSX). Fundamental plasma and neutral quantities are analyzed, and error reduction rates are compared against theoretical expectations. The statistical error, bias, and time integration error are fully characterized; however, quantification of the discretization error remains challenging because of the complex grid geometries used in EMC3-EIRENE. The commonly used volume averaged relative change metric is shown to systematically underestimate the statistical error, highlighting a critical flaw in EMC3-EIRENE analysis, where convergence is claimed despite significant noise remaining in the simulation solution. Dominant contributions of the time integration error are shown to differ in stellarator simulations compared to tokamak simulations, related to the relative importance of cross-field transport between the two devices. Based on these results and existing literature, we establish best practices towards improved accuracy and efficiency in general stellarator modeling with EMC3-EIRENE.
Comments21 pages, 7 figures, submitted to Nuclear Fusion
