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Infrared constrained equilibria and application to snowflake divertor studies
Nuclear Materials and Energy ( IF 2.6 ) Pub Date : 2020-11-17 , DOI: 10.1016/j.nme.2020.100835
J.T. Wai , P.J. Vail , A.O. Nelson , Z.A. Xing , C. Lasnier , E. Kolemen

One of the challenges of the snowflake divertor (SFD) configuration is finding a reliable means of reconstructing the magnetic field geometry in the divertor. Since the SFD (and other advanced divertors) have multiple field nulls, there is a large region with shallow flux gradients that is difficult to resolve accurately using external diagnostics. In this work we present a technique that uses heat flux measured by the infrared television (IRTV) camera to improve SFD reconstruction. This is relevant for purposes of control, since the SFD is topologically unstable and requires active feedback on the shape [E. Kolemen, et. al., Nucl. Fusion, 58, 6 (2018)], and analysis, since reconstructions provided by other algorithms such as EFIT [L. Lao, et. al., Nucl. Fusion, 25, 11 (1985)] can mis-characterize the shape and even the snowflake type (plus or minus). The technique identifies the spatial position of the two x-points located in the SFD based on characteristics of the heat flux such as the strike point location and power distribution. The inferred x-point positions are then used as a constraint in fitting new equilibria using the TokSys suite of software. This procedure is applied to ~800 DIII-D SFD timeslices and reduces the summed strike point errors from an average 9.4 cm to 0.9 cm. The newly-created x-point constrained equilibria are compared to kinetic reconstructions and an average 16% reduction in the edge current is observed. This is correlated via a simple linear relationship to the shape constraints. Other changes in the pedestal structure are observed, but more work must be done to incorporate the IRTV constraint directly into kinetic solvers to obtain integrated solutions.



中文翻译:

红外约束平衡及其在雪花偏滤器研究中的应用

雪花偏滤器(SFD)配置的挑战之一是找到一种可靠的方法来重建偏滤器中的磁场几何形状。由于SFD(和其他高级偏滤器)具有多个场零点,因此存在一个较大的区域,具有较浅的通量梯度,很难使用外部诊断程序精确解析。在这项工作中,我们提出了一种利用红外电视(IRTV)摄像机测量的热通量来改善SFD重建的技术。这与控制目的相关,因为SFD在拓扑上不稳定,并且需要对形状[E. Kolemen等。等,Nucl。Fusion,58,6(2018)]和分析,因为其他算法(例如EFIT [L. 老挝等 等,Nucl。融合,25岁,11(1985)]可能会错误地描述形状,甚至雪花类型(正负)。该技术基于热通量的特征(例如击中点位置和功率分布)来识别位于SFD中的两个x点的空间位置。然后,使用TokSys软件套件将推断的x点位置用作约束条件,以拟合新的平衡点。此过程适用于800 DIII-D SFD时间片,将总的打击点误差从平均9.4 cm减少到0.9 cm。将新创建的x点约束平衡与动力学重建进行比较,观察到边缘电流平均降低16%。这通过简单的线性关系与形状约束相关联。观察到了基座结构的其他变化,但是必须做更多的工作才能将IRTV约束直接合并到动力学求解器中以获得集成解。

更新日期:2020-11-25
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