Characterizing magnetized plasmas with dynamic mode decomposition
Characterizing magnetized plasmas with dynamic mode decomposition
复制标题
通过动态模式分解表征磁化等离子体
作者：
A. Kaptanoglu;K. Morgan;C. Hansen;S. Brunton
准确有效的等离子体模型对于理解和控制实验装置是必不可少的。现有的磁流体动力学或动力学模型是非线性的，计算密集型的，并且可能难以解释，而往往只是近似真实的动态。在这项工作中，最近在流体动力学领域开发的数据驱动技术被用来开发可解释的等离子体降阶模型，在准确性和效率之间取得平衡。特别是，动态模式分解（DMD）是用来提取时空磁相干结构的实验和模拟数据集的HIT-SI实验。从HIT-SI实验的三维磁性表面探针进行了分析，沿着与同伴模拟与合成内部磁性探针。比较了DMD算法的许多主要变体，包括稀疏促进和优化的DMD。优化的DMD导致最高的整体预测精度，而稀疏促进DMD产生物理上可解释的模型，避免过拟合。这些DMD算法揭示了几种相干磁模式，为内部等离子体结构提供了新的物理见解。这些模式随后被用来发现一个以前未观察到的三维结构在模拟中，旋转的第二注入谐波。最后，使用实验可访问的位置从探针的数据，DMD确定了一个电阻扭结模式，一个普遍存在的不稳定性磁化等离子体。
Accurate and efficient plasma models are essential to understand and control experimental devices. Existing magnetohydrodynamic or kinetic models are nonlinear, computationally intensive, and can be difficult to interpret, while often only approximating the true dynamics. In this work, data-driven techniques recently developed in the field of fluid dynamics are leveraged to develop interpretable reduced-order models of plasmas that strike a balance between accuracy and efficiency. In particular, dynamic mode decomposition (DMD) is used to extract spatio-temporal magnetic coherent structures from the experimental and simulation datasets of the HIT-SI experiment. Three-dimensional magnetic surface probes from the HIT-SI experiment are analyzed, along with companion simulations with synthetic internal magnetic probes. A number of leading variants of the DMD algorithm are compared, including the sparsity-promoting and optimized DMD. Optimized DMD results in the highest overall prediction accuracy, while sparsity-promoting DMD yields physically interpretable models that avoid overfitting. These DMD algorithms uncover several coherent magnetic modes that provide new physical insights into the inner plasma structure. These modes were subsequently used to discover a previously unobserved three-dimensional structure in the simulation, rotating at the second injector harmonic. Finally, using data from probes at experimentally accessible locations, DMD identifies a resistive kink mode, a ubiquitous instability seen in magnetized plasmas.