High-energy-density plasmas generation on GEKKO-LFEX laser facility for fast-ignition laser fusion studies and laboratory astrophysics

Abstract

The world's largest peta watt (PW) laser LFEX, which delivers energy up to 2 kJ in a 1.5 ps pulse, has been constructed beside the GEKKO XII laser at the Institute of Laser Engineering, Osaka University. The GEKKO-LFEX laser facility enables the creation of materials having high-energy-density which do not exist naturally on the Earth and have an energy density comparable to that of stars. High-energy-density plasma is a source of safe, secure, environmentally sustainable fusion energy. Direct-drive fast-ignition laser fusion has been intensively studied at this facility under the auspices of the Fast Ignition Realization Experiment (FIREX) project.In this paper, we describe improvement of the LFEX laser and investigations of advanced target design to increase the energy coupling efficiency of the fast-ignition scheme. The pedestal of the LFEX pulse, which produces a long preformed plasma and results in the generation of electrons too energetic to heat the fuel core, was reduced by introducing an amplified optical parametric fluorescence quencher and saturable absorbers in the front-end system of the LFEX laser. Since fast electrons are scattered and stopped by the strong electric field of highly ionized high-Z (i.e. gold) ions, a low-Z cone was studied for reducing the energy loss of fast electrons in the cone tip region. A diamond-like carbon cone was fabricated for the fast-ignition experiment. An external magnetic field, which is demonstrated to be generated by a laser-driven capacitor-coil target, will be applied to the compression of the fuel capsule to form a strong magnetic field to guide the fast electrons to the fuel core. In addition, the facility offers a powerful means to test and validate astronomical models and computations in the laboratory. As well as demonstrating the ability to recreate extreme astronomical conditions by the facilities, our theoretical description of the laboratory experiment was compared with the generally accepted explanation for astronomical observations.

Novel aspects of direct laser acceleration of relativistic electrons

“…Recent developments (Daido et al 1986;Courtois et al 2005;Fujioka et al 2012Fujioka et al , 2013Albertazzi et al 2014) in the generation of strong magnetic fields on large scales using high-power laser techniques raise the question as to what use might be made of magnetic fields with flux densities that perhaps even reach 1 kT. Theoretical work also continues to indicate that self-generated longitudinal magnetic fields can occur in laser-plasma interactions (Liu et al 2013).…”

Theory of fast electron transport for fast ignition

“…laser-driven coils (Daido et al 1986, Fujioka et al 2012, Fujioka et al 2013. A body of simulation work has been carried out at LLNL on the assembly of such fields, and the characterization of their advantages for electron transport, which we shall review here.…”

“…Work is ongoing to elucidate the difference in field dynamics. Magnetic field generation by laser-driven coils (Daido et al 1986) was demonstrated experimentally in the 1980s, and has recently been suggested as a divergence mitigation approach for fast ignition (Fujioka et al 2012). In this scheme, a coil connects two plates, one of which is struck by a kJ-class, long pulse (∼ ns) laser.…”

“…A large, transient current flows through the coil and induces a large magnetic field. Experiments at GEKKO-XII (Fujioka et al 2012) have recently made fields of 10 MG. Ref. (Courtois et al 2005) reports smaller-scale experiments at the VULCAN laser which generated fields of 0.1 MG, as well as a simple model of the system.…”

New scheme to trigger fusion in a compact magnetic fusion device by combining muon catalysis and alpha heating effects

“…The surface muon production [20] from proton beam interaction with a solid target presents a local maximum in the range of 300-350 MeV [19,[21][22][23][24] . Experiments on laserdriven proton acceleration by high power, ps laser pulse interaction with ultrathin solid targets or with specific solid target configuration could be planned and performed in existing kJ/PW laser facilities as the GEKKO-LFEX [25,26] , the ORION [27] and the PETAL [28,29] . Recent development of kJ/PW laser systems [30] in worldwide laser facilities enable to perform preliminary experiments on muon production by proton beam interaction with solid targets and investigate fusion process in magnetized plasmas with applications to astrophysics [28][29][30] or energy production [25,26,[28][29][30] .…”