Study of electron exhaust jet and current-driven instabilities in kinetic magnetic reconnection using laser-powered capacitor coils*

Magnetic reconnection is a ubiquitous phenomenon in space and astrophysical plasmas that rapidly releases magnetic energy. Plasma kinetic instabilities often play an important role in the required dissipation. We conducted kilojoule laser-powered kinetic reconnection experiments with capacitor-coils [1-3] to study electron outflow jets using collective Thomson scattering. Thomson scattering shows the existence of electron-acoustic waves (EAW) with phase velocity near the electron thermal speed, which suggests a non-Maxwellian distribution overcoming Landau damping. We also observed bursty and asymmetric ion-acoustic waves (IAW), confirming the existence of the electron jet and the current-driven ion-acoustic instabilities (IAI). The amplitude of both EAW and IAW exhibits correlated bursts with a frequency that matches the lower-hybrid frequency. Specially designed local Particle-In-Cell simulation shows that the current-driven IAI can form a double layer and induce electron two-stream instability generating EAW that are consistent with the measurements. Our experiments and simulations demonstrate that the electron outflow jet is unstable and can dissipate energy through electron-ion coupling. The combination of collective Thomson scattering and the laser-powered experiments opened up a new avenue to study kinetic physics in reconnection. 

 

[1] L. Gao et al., Ultrafast proton radiography of the magnetic fields generated by a laser-driven coil current. Physics of Plasmas, 23(4):043106, 2016. 

[2] A. Chien et al., Study of a magnetically driven reconnection platform using ultrafast proton radiography. Physics of Plasmas, 26:062113, 2019. 

[3] A. Chien et al., Direct measurement of non-thermal electron acceleration from magnetically driven reconnection in a laboratory plasma, submitted.