Pressure Anisotropy Probe for the Terrestrial Reconnection Experiment (TREX)*

The Terrestrial Reconnection Experiment (TREX) at the Wisconsin Plasma Astrophysics Laboratory (WiPAL) studies magnetic reconnection primarily in the collisionless regime. In this regime, electron pressure anisotropy is expected to develop, deviating from traditional Hall reconnection dynamics and driving formation of large-scale current layers. In order to measure the anisotropy, a multi-tip electromagnetic probe similar to the M-probe described by Shadman [1], consisting of 32 Langmuir probe tips and two magnetic coils, has been constructed. Each tip is biased to a different potential, simultaneously measuring discrete parts of the full I-V characteristic. Pulsing the coil then locally increases the magnetic field, creating a magnetic mirror force to reflect electrons with large values of $v_{\perp}/v$. The change in electron velocity modifies the I-V characteristics and can be used to infer $p_{\parallel}/p_{\perp}$. Analysis with the new probe will be presented. [1] K. Shadman, Physics of Plasmas (2004).