Micro-channel design efficiently creates high-energy electron accelerations

Plasmas produced by high intensity lasers are capable of accelerating particles to high energies over very short distances. By focusing high-power lasers on targets, laser-plasma interactions (LPIs) can be used to generate high energy electrons, ions, high-order harmonics, and electron-positron jets. However, electron acceleration with these lasers and solid-density targets is difficult to predict or control due to the lack of understanding of a byproduct generated by the lasers themselves known as pre-plasma. Pre-plasma comes from the pre-pulse of the laser interacting with the target, which can form over time and produce a broad spray of particles that falls off sharply in energy, interfering with secondary processes such as proton acceleration.

Snyder et al. came up with a new way to better control the electron acceleration process — by eliminating the role of pre-plasma altogether. They propose using a pre-formed channel to direct both the laser pulse and electrons to enhance the laser-target interaction. They tested a micro-channel plate (MCP) that was 300 µm thick with 5 µm diameter channels with Scarlet, an ultrahigh power laser at The Ohio State University. According to their test results, the MCP produced far more superponderomotive electrons (electrons above the natural temperature scale for LPIs with pre-plasma) compared to typical targets like copper (Cu) foils, suggesting a different type of acceleration mechanism. This makes the MCP better than flat Cu foils because there can be more control over the interaction and the electrons produced and the laser intensity can be preserved for a longer time.

According to the authors, although this is not the first study looking at LPIs and MCPs, their approach is a first experiment demonstrating the advantages of MCPs in creating high energy particles to be used for ion acceleration or secondary radiation sources (x-ray, γ-ray and Terahertz radiation), since most existing research has been based only on theoretical and computational calculations. Other applications for these microstructures are currently being further investigated.

Source: “Relativistic laser driven electron accelerator using micro-channel plasma targets,” by J. Snyder, L. L. Ji, K. M. George, C. Willis, G. E. Cochran, R. L. Daskalova, A. Handler, T. Rubin, P. L. Poole, D. Nasir, A. Zingale, E. Chowdhury, B. F. Shen, and D. W. Schumacher, Physics of Plasmas (2019). The article can be accessed at https://doi.org/10.1063/1.5087409 .