Particle Acceleration and Ion Acoustic Waves during Magnetically Driven Reconnection using Laser-Powered Capacitor Coils*

Magnetic reconnection is a ubiquitous phenomenon in astrophysical plasmas that rapidly converts magnetic energy into some combination of plasma flow energy, thermal energy, and non-thermal energetic particles in the presence of a magnetic topology change. Over the past decade, our team has developed a new experimental platform to study magnetically driven reconnection using strong coil currents powered by high power lasers [1] at low plasma beta, typical conditions under which reconnection is energetically important. KJ-class lasers were used to drive parallel currents to reconnect MG-level magnetic fields in a quasi-axisymmetric geometry, resemble to the Magnetic Reconnection Experiment or MRX [2], and thus this platform is termed micro-MRX. In this presentation, we report two major findings of our work on direct measurement of particle acceleration [3] and observation of ion acoustic waves [4] during anti-parallel reconnection in the micro-MRX. For the first time, we have successfully measured the energetic electrons generated by magnetic reconnection using particle spectrometers in a laboratory plasma. The angular dependence of the measured electron energy spectrum and the resulting accelerated energies, supported by particle-in-cell simulations, indicate that direct electric field acceleration by the out-of-plane reconnection electric field is at work [3]. Furthermore, we observe a sudden onset of ion acoustic bursts measured by collective Thomson scattering in the exhaust of magnetic reconnection, which are followed by electron acoustic bursts with electron heating and bulk acceleration [4]. These results demonstrate that the micro-MRX platform offers a novel and unique approach to study magnetic reconnection in the laboratory beyond the capabilities provided by typical magnetized plasma experiments such as MRX and the upcoming FLARE or Facility for Laboratory Reconnection Experiments [5]. Implications of these laboratory findings to space and astrophysical scenarios and future work on studying other particle acceleration mechanisms and ion acoustic waves will be discussed.