38 / 2023-04-05 21:09:01

Ion-electron non-equilibrium in ICF hot-spot ignition

Ion-electron non-equilibrium, ignition condition, electron-ion energy exchange

惯性约束聚变物理学 > 内爆和不稳定性

        American scientists have achieved inertial confinement fusion ignition on its national ignition facility (NIF), after more than ten years of great efforts. However, there still exist many scientific problems to be thoroughly studied, and deep understandings of these problems are of great significance for achieving a repeatable and reliable or an even higher-gain fusion ignition. Ion-electron non-equilibrium within the hot spot is one of them.

        The ion-electron non-equilibrium phenomenon could be inferred from NIF high-foot implosions. It is observed from many high-foot shots that the x-ray enhancement factors are less than unity, which is not self-consistent and is caused by assuming T_e = T_i. And from this non-consistency, we could infer that ion-electron non-equilibrium exists in the high-foot implosions and the ion temperature could be ~9% larger than the equilibrium temperature^[1].

        With the ion-electron non-equilibrium model in which the hot-spot ion temperature is higher than its electron temperature, the hot-spot nuclear reactions are enhanced while its energy leaks are considerably reduced, as compared with the commonly used equilibrium model. Theoretical analysis shows that the hot-spot ignition conditions would be significantly relaxed with the ion-electron non-equilibrium model ^[2]. And simulations show that shocks could be utilized to create and maintain non-equilibrium conditions within the hot spot.

        Modelling of the electron-ion energy exchange rate of the hydrogen plasmas is essential for a reliable simulation of the ion-electron non-equilibrium within the hot spot. Molecular dynamics simulations are carried out to assess the electron-ion energy relaxation rates ^[3], and special attention is paid to the quantum diffraction effects of the hot and dense hydrogen plasmas. With an improved electron-ion energy exchange model, it found that the quantum diffraction effects are beneficial for a more apparent hot-spot ion-electron non-equilibrium.



[1] Z. F. Fan, Y. Y Liu, Bin Liu, et al., Non-equilibrium between ions and electrons inside hot spots from National Ignition Facility experiments, Matter and Radiation at Extremes 2, 3-8 (2017).

[2] Z. F. Fan, J. Liu, B. Liu, et al., Ignition conditions relaxation for central hot-spot ignition with an ion-electron non-equilibrium model, Physics of Plasmas 23, 010703 (2016).

[3] C. Z. Gao, C. B. Zhang, Y. Cai, et al., Assessment of the electron-proton energy relaxation rates extracted from molecular dynamics simulations in weakly-coupled hydrogen plasmas, Phys. Rev. E 107, 015203 (2023).