Estimation of electron temperature using gated X-ray pinhole images of magnetic reconnection experiments at the NIF*

We present results from high-aspect ratio magnetic reconnection experiments driven at the National Ignition Facility. In these experiments, 40 beams are tiled to produce two elongated laser-driven plumes which are self-magnetized by the Biermann battery effect [1]. As these plumes expand, they collide and drive magnetic reconnection. A gated X-ray framing camera with micro-channel plate (MCP) detector produces 16 filtered images of the formation and evolution of both the plumes and current sheet up to 8 ns after the lasers fire. The 2-dimensional electron temperature is estimated by taking the ratio of intensity of these images obtained with different filters, a technique developed for the sub-keV temperatures expected in these experiments [2]. The data show that the plasma plumes are initially several hundreds of eV hot and collide at ~ 2 ns after initial laser irradiation. As the current sheet forms, we observe that it becomes hotter than the plumes, and its temperature remains constant throughout the rest of the experimental time-frame. We discuss the interplay of shock heating, radiative cooling, and magnetic reconnection in the energy balance of the current sheet.

 

[1] Fox, et al. arXiv:2003.06351 (2020)

[2] Schaeffer, et al. RSI (2020)