Spherically Imploding Plasma Liners as a Standoff Magneto-Inertial-Fusion Driver

Spherically imploding plasma liners formed by merging hypersonic plasma jets are a proposed compression driver for magneto-inertial fusion (MIF). Under the ARPA-E ALPHA program, the Plasma Liner Experiment--ALPHA (PLX-$\alpha$) plans to culminate in forming spherically imploding sub-fusion-scale plasma liners [1] via 36 merging hypersonic plasma jets (with initial $n_i \sim 2\times 10^{16}$~cm$^{-3}$, $v_{\rm jet} \approx$ 50~km/s, mass $\sim 1$~mg, and various gas species). We summarize experimental results on the formation of a conical section of spherically imploding plasma liners by merging six [2] and seven plasma jets. Data from fast-framing-cameras, visible spectrometers, and a multi-chord interferometer have been analyzed to assess (i) ion heating (and associated liner-Mach-number degradation) due to collisional shock formation between merging jets [3], and (ii) liner uniformity upon jet merging. These data are benchmarking code calculations, which will set requirements on fusion-scale plasma liners. [1] S. C. Hsu and Y. C. F. Thio, J. Fusion Energ.~{\bf 37}, 103 (2018); [2] S. C. Hsu et al., {\em IEEE Trans.\ Plasma Sci.}~{\bf 46}, 1951 (2018); [3] S. J. Langendorf et al., submitted (2018); https://arxiv.org/abs/1805.09933.