Plasmas in supercritical fluid with densely populated clusters

In supercritical fluid (SCF) with dense population of stable clusters ($\sim 1000 \mbox{ mm}^{-3}$; mean size $\sim$ 200 nm)$^a$, elongated plasmas are produced along the optical axis of laser pulse (532 nm, 6 ns, 400 mJ, peak intensity $\sim 1$ TW/cm$^2$). The plasma has a strong afterglow with the lifetime up to 1 $\mu$s, increasing with the number density of clusters. For argon SCF plasmas, the electron temperature and density estimated from continuum emission spectra are $\sim 1$ eV and $\sim 10^{21} \mbox{cm}^{-3}$, respectively, corresponding to a high Coulomb coupling constant of the order of unity. The radial diffusion is weak, smaller than the diffusion length predicted by the one-component plasma theory for moderate to strong Coulomb coupling$^b$. These observations suggest that the presence of clusters strongly affects the particle and energy transport processes. $^a$S.T. Lee et al., APS Gaseous Electronics Conf.(2019). $^b$Daligault, Phys. Rev. Lett. 108 (2012).