Princeton Center for Heliophysics Seminar

Using topology to locate the position where fully three dimensional reconnection occurs

Magnetic flux ropes are bundles of twisted magnetic fields and their associated currents. They are common on the surface of the sun (and presumably all other stars) and are observed to have a large range of sizes and lifetimes. Two “kink” unstable ropes are generated in a background plasma in the Large Plasma Device at UCLA. When they collide fully 3D magnetic reconnection occurs. In a reconnection process magnetic energy is transformed to heat, energized particles and waves. In two dimensional magnetic reconnection, involving neutral sheets and magnetic islands it is generally a straightforward task to recognize reconnection sites when detailed data sets or simulations are available. In fully three dimensional reconnection their analogues can be challenging to identify. In this experiment the time dependent magnetic fields, plasma flows, electron temperature, plasma density, space charge and inductive electric fields were measured at over 42,000 spatial positions, 16,000 times steps requiring several million rope collision experiments. Magnetic field lines are followed in 3D and used to derive quasi-seperatrix layers (QSL), extended surfaces within which reconnection occurs. It turns out that QSL’s do not fully capture areas of reconnection. We have used additional topological quantities : the winding number (which measures the entanglement of pairs of field lines), magnetic twist, writhe and helicity to calculate a new quantity, the reconnection activity (RA). The RA identifies subregions of magnetic field lines which are reconnecting. It is demonstrated that the regions with the highest reconnective activity do not always coincide with the largest QSL signatures are, thus indicating this is a more complete methodology for quantifying reconnective activity than standard methods. This framework can serve as a model for reconnection analysis in future studies, in combination with established methods for identifying the specific form of reconnection once its location is established.

Date & Time

April 09, 2021 | 2:00pm – 3:00pm

Location

Virtual Meeting

Speakers

Walter Gekelman

Speaker Affiliation

UCLA