How is helicity (and twist) partitioned in magnetohydrodynamic simulations of reconnecting magnetic flux tubes?
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Magnetic helicity conservation provides a convenient way to analyze specific properties (namely, the linkage and twist) of reconnecting flux tubes and yield additional insight into the pre- and post-reconnection states of magnetic structures in the solar atmosphere. A previous study considered two flux tubes with footpoints anchored in two parallel planes. They showed that reconnection would add self-helicity equivalent to a half turn of twist to each flux tube. We address a related and fundamental question here: if two flux tubes anchored in a single plane reconnect, what are the resulting twists imparted to each of the reconnected tubes? Are they equal and do they have a simple exact value independent of footpoint location? To do this, we employ a new (computationally efficient) method which subdivides each flux tube into distinct elements and calculates the mutual helicity of many elemental pairs, the sum of which determines the self-helicity of the overall flux tube. Having tested the method using a simple analytical model, we apply the technique to a magnetohydrodynamic simulation where initially untwisted magnetic flux tubes are sheared and allowed to reconnect (based on a previous reconnection model). We recover values of self-helicity and twist in the final end state of the simulations which show excellent agreement with theoretical predictions.
Threlfall , J , Wright , A N & Hood , A W 2020 , ' How is helicity (and twist) partitioned in magnetohydrodynamic simulations of reconnecting magnetic flux tubes? ' , Astrophysical Journal , vol. 898 , no. 1 , 1 . https://doi.org/10.3847/1538-4357/ab9c2a
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DescriptionFunding: STFC through the Consolidated grant, ST/N000609/1, to the University of St Andrews.
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