Thesis Defense |
Events on Wednesday, November 5th, 2025
- Laboratory Investigation of Collisionless Kinetic Effects and 3D Topological Triggers for Magnetic Reconnection
- Time: 11:00 am - 1:00 pm
- Place: Chamberlin 5310
- Speaker: Paul Gradney
- Abstract: Magnetic reconnection is a fundamental plasma process responsible for the rapid conversion of magnetic energy into particle energy. This process occurs ubiquitously in astrophysical, space, and laboratory plasmas, including solar flares, Earth's magnetosphere, and fusion devices. Despite its importance, key questions remain, including how reconnection dynamics are modified in the collisionless kinetic regime, and what mechanisms trigger fast reconnection in three-dimensional (3D) systems as they transition from stable or quasi-stable magnetic configurations to configurations that enable rapid energy release.
This thesis presents experimental studies of collisionless magnetic reconnection using the Terrestrial Reconnection EXperiment (TREX) at the Wisconsin Plasma Physics Laboratory (WiPPL). To minimize collisional effects and access the kinetic regime relevant to space plasmas, a reconnection Drive Cylinder was developed. This system increases both the effective system size and the driving rate of reconnection, enabling TREX to reach a regime where electron dynamics are dominated by kinetic rather than collisional processes. Technical details of the Drive Cylinder design, including its coil configuration and magnetic field shaping, are presented along with measurements of its performance.
Using the 3-coil TREX configuration, the dynamics of 3D reconnection were investigated in a laboratory-generated mini-magnetosphere. Observations demonstrate that the explosive onset of reconnection can be triggered by a bifurcation of the magnetic topological structure. In particular, the rapid approach and crossing of separatrix surfaces led to the bifurcation of magnetic null points, restructuring of separator lines, and a marked increase in the reconnection electric field along the separator. These results provide experimental evidence that geometric reconfiguration of a 3D magnetic topology can initiate the onset of fast reconnection. The findings have broad implications for understanding space weather, astrophysical explosions, and relaxation events in magnetically confined laboratory plasmas. - Host: Jan Egedal