Anisotropic Electron Heating during Electron-Only Magnetic Reconnection in PHASMA

Electron-only reconnection is a variant of magnetic reconnection without significant ion involvement, which has recently been observed in the terrestrial magnetosheath and has received considerable attention due to its likely role in the energy cascade of turbulent magnetized plasmas. Different electron energization mechanisms usually favor electron acceleration along different directions and occur in different regions of reconnection. Therefore, spatially resolved electron velocity distribution function (EVDF) measurements along specific directions are required to elucidate the underlying electron energization mechanisms. In the PHAse Space MApping (PHASMA) facility, the incoherent Thomson scattering system has been upgraded to enable 3D EVDF measurements via employing two injection paths and two collection paths. Going beyond our recent work [Shi et al., Phys. Rev. Lett. 128, 025002 (2022)], both electron temperatures parallel (T_e||) and perpendicular (T_e⟂) to guide field have been measured during electron-only reconnection. The initial results indicate modest electron temperature anisotropies, T_e|| / T_e⟂ ~1.5, exist around the separatrix. One 2D spatial map of T_e|| and T_e⟂ will also be reported in the spirit of identifying possible electron energization mechanisms.