The Effects of Magnetic Pressure and Tension in Null Points Dynamics in TREX Experiment

Null points are created using the TREX (The Terrestrial Reconnection EXperiment) Drive Cylinder [1], a thirteen-coil cylindrical magnetic field driver, housed within the Big Red Ball (BRB) [2] at the University of Wisconsin–Madison. Collisionless magnetic reconnection is driven in TREX Drive Cylinder [3]. As the reconnection layer advances toward the center, magnetic null points emerge. These null points are then driven apart by magnetic pressure and tension forces. Each null point’s fan structure is deflected outward, forming a cone-like shape. The magnetic pressure force originates from the strong magnetic field outside the cone and pushes inward, perpendicular to the cone's side surface. The magnetic tension force arises from the high curvature of field lines intersecting the base of the cone and drags outward, normal to the surface. B-dot probes were used for collecting magnetic field data. This poster presents an analysis of the experimental data, addressing how the null points move and how much energy is released from field line shortening.

[1] Olson, J., Egedal, J., Greess, S., Myers, R., Clark, M., Endrizzi, D., Flanagan, K., Milhone, J., Peterson, E., Wallace, J., Weisberg, D., & Forest, C. (2016). Experimental demonstration of the collisionless plasmoid instability below the ion kinetic scale during magnetic reconnection. Physical Review Letters, 116(25), 255001. https://doi.org/10.1103/PhysRevLett.116.255001

[2] Forest, C. B., Flanagan, K., Brookhart, M., Clark, M., Cooper, C. M., Désangles, V., ... & Zweibel, E. (2015). The Wisconsin Plasma Astrophysics Laboratory. Journal of Plasma Physics, under consideration. arXiv:1506.07195v2

[3] Gradney, P., Egedal, J., Barnhill, I., Flores-García, R., Greess, S., Kuchta, C., Olson, J., Wallace, J., Yu, X., & Forest, C. (2023). Implementation of a drive cylinder for low collisional experiments on magnetic reconnection. Review of Scientific Instruments, 94(12), 123503. https://doi.org/10.1063/5.0175812