Rapid electron heating in the reconnection inflow on TREX*

The Terrestrial Reconnection Experiment (TREX) has been designed to study the regime of collisionless magnetic reconnection in which kinetic features such as electron pressure anisotropy develop unimpeded by collisions [1]. This fully kinetic regime is limited to Lundquist numbers of S>10ε(m_i/m_e)L/d_i, where ε<1 is an experimental scale factor and L is the system size [2]. TREX continues to assess the presence of pressure anisotropy in experiments with S~10⁴-10⁵ in Hydrogen, well within the collisionless regime. During these events, electron heating is observed along the inflow jets from T_e~5 eV to T_e~20 eV in 1 collision time (τ_e~2 μs). This heating is too fast to be thermalized by collisions, and given the expected anisotropy, is likely primarily T_e|| heating. Additionally, TREX observes reconnection rates of E_rec~V_AB, much faster than the expected rate of E_rec~(0.1)V_AB, over a wide range of plasma species and experimental parameters. Current studies are looking into the relationship between the external drive and the global geometry and how these affect the kinetic structure of reconnection on TREX.

[1] Egedal J. et al., Nature Phys., 8, 321 (2012).

[2] Le A. et al., J. Plasma Phys., 81, 305810108 (2015).