Strongly coupled plasma states produced in supercritical fluids

Abstract

High-density strongly coupled plasma (SCP) states are ubiquitous in the universe including the inner layers of stars, the core of Jupiter-like planets, and perhaps many electrical discharges in high pressure atmospheres of planets. To understand transport and thermodynamic properties of such states, we built an experiment to produce high-density SCPs in supercritical fluid (SCF) using laser pulse and high voltage bias. The SCF medium is chosen to minimize energy loss via phase transitions and particle transport [1]. For ns laser pulse on argon SCF at 100 bar, SCPs are generated with electron density ~ 1027 m-3 and temperature ~ 1 eV, corresponding to the Coulomb coupling parameter of the order of unity [2]. Combination with high voltage bias extends the lifetime of the SCP state from a few 100s ns to a few µs, opening an opportunity for precision measurements. For fs laser pulse, SCPs are generated with similar electron density and temperature, which suggests that the ionization potential reduction is the dominant ionization mechanism to attain the high electron density. This implies that the medium density determines the electron density of the SCP. *This work was supported by the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT (Nos. 2019R1A2C3011474, 2022M3H4A1A04074153, and RS-2022- 00154676). [1] Seungtaek Lee et. al., Quasi-equilibrium phase coexistence in single component supercritical fluids, Nature Communications 12, 4630 (2021) [2] Seungtaek Lee, Juho Lee et. al., Characterization of strongly coupled plasmas produced in argon supercritical fluids, Plasma Physics and Controlled Fusion 64, 095010 (2022)