The 6th International Conference on Matter and Radiation at Extremes (ICMRE2023)

77 / 2023-04-13 02:27:30

Recent progress of experimental studies on fast- ignition inertial fusion energy

ICF,laser,direct drive,fast ignition

Inertial Confinement Fusion Physics > Drivers, targets and diagnostics-II

 Interactions between the picosecond PW laser pulse and a plasma generate an electron beam with relativistic energy, called a relativistic electron beam (REB). This REB heats the high-density plasma in the REB-based fast ignition scheme. The advantage of the REB-based scheme is the high energy conversion efficiency from laser to REB (>30%). On the other hand, the average REB energy must be below 3 MeV to heat locally and efficiently a tiny volume of the high-density plasma, and REB has a large divergence angle (> 90 deg.) [1]. We are conducting the fast-ignition experiments using GEKKO-XII, a nanosecond TW laser system, to generate a high-density plasma by an implosion, and LFEX laser, a picosecond PW laser system, to heat the high-density plasma instantaneously. We have introduced plasma mirrors to the LFEX [2] to significantly improve the pulse contrast for heating the plasma by low-energy REB and shortening the distance between the high-density plasma and the interaction region so that the heat can diffusively propagate from the directly heated interaction region to the high-density region[3]. In addition, externally applying a laser-generated magnetic field improves the directionality of REBs, and the heating efficiency by collisions between REBs and ions (drag heating) is successfully enhanced [4]. Our results show that plasmas above solid density can be heated with 10% of the total efficiency by drag and thermal diffusion heating mechanisms. The heating efficiency depends on the plasma density. We have proposed a solid ball fuel as a target for avoiding the breakup of the imploding plasma due to hydrodynamic instability [5]. We have also conducted experiments using a solid ball target to produce high-density plasma with a three-step pulse. We are also developing a liquid deuterium-containing solid ball for the world's first fast ignition experiment with deuterium plasma.

[1]       S. Fujioka et al., Heating Efficiency Evaluation with Mimicking Plasma Conditions of Integrated Fast-Ignition Experiment, Phys. Rev. E 91, 063102 (2015).

[2]       Y. Arikawa et al., Ultrahigh-Contrast Kilojoule-Class Petawatt LFEX Laser Using a Plasma Mirror, Appl. Opt. 55, 6850 (2016).

[3]       K. Matsuo et al., Petapascal Pressure Driven by Fast Isochoric Heating with a Multipicosecond Intense Laser Pulse, Phys. Rev. Lett. 124, 035001 (2020).

[4]       S. Sakata et al., Magnetized Fast Isochoric Laser Heating for Efficient Creation of Ultra-High-Energy-Density States, Nat. Commun. 9, 3937 (2018).

[5]       H. Sawada et al., Development of 4.5 KeV Monochromatic X-Ray Radiography Using the High-Energy, Picosecond LFEX Laser, J. Phys. Conf. Ser. 717, 7 (2016).