Pressure Anisotropy Measurements on the Terrestrial Reconnection Experiment

The Terrestrial Reconnection Experiment (TREX) at the Wisconsin Plasma Physics Laboratory (WiPPL) studies collisionless magnetic reconnection. In this regime, electron pressure anisotropy should develop, deviating from Hall reconnection dynamics and driving large-scale current layer formation. This anisotropy has been seen in spacecraft such as Wind, but has not been detected easily in laboratory experiments [1]. In order to measure this anisotropy, a multi-directional Langmuir probe has been designed and constructed, containing four external tips and four shielded tips arranged evenly around the circumference of the probe shaft. Shielding and probe orientation relative to the magnetic field (measured by a 3D magnetic pickup loop) modify the current-voltage characteristic due to differences in the number of electrons entering the probe from each direction. The changes in the I-V curve thus display the extent of observed anisotropy in the collisionless reconnection region. Since the Langmuir tip radius is smaller than the Larmor radius, gyromagnetic effects can be ignored. Results and analysis from the probe are presented.

[1] J. Egedal et al., Nature Phys. (2012).