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Laser plasma interactions in a relativistic parameter regime have been intensively investigated for studying the possibility of fast ignition in inertial confinement fusion ͑ICF͒. Using ultra-intense laser systems and particle-in-cell ͑PIC͒ simulation codes, relativistic laser light self-focusing, super hot electrons, ions, and neutron production, are studied. The experiments are performed with ultra-intense laser with 50 J energy, 0.5-1 ps pulse at 1053 nm laser wavelength at a laser intensity of 10 19 W/cm 2. Most of the laser shots are studied under preformed plasma conditions with a 100 m plasma scale length condition. In the study of laser pulse behavior in the preformed plasmas, a special mode has been observed which penetrated the preformed plasma all the way very close to the original planar target surface. On these shots, super hot electrons have been observed with its energy peak exceeding 1 MeV. The energy transport of the hot electrons has been studied with making use of K␣ emissions from a seeded metal layer in planar targets. The details of ion acceleration followed by beam fusion reaction have been studied with neutron spectrometers. Laser ponderomotive force self-focusing and hot electron generation have been applied to a compressed core to see the effect of heating by injecting 12 beams of 100 ps, 1 TW pulses.

Based on the successful result of fast heating of a shell target with a cone for heating beam injection at Osaka University in 2002 using the PW laser (Kodama et al 2002 Nature 418 933), the FIREX-1 project was started in 2004. Its goal is to demonstrate fuel heating up to 5 keV using an upgraded heating laser beam. For this purpose, the LFEX laser, which can deliver an energy up to10 kJ in a 0.5-20 ps pulse at its full spec, has been constructed in addition to the Gekko-XII laser system at the Institute of Laser Engineering, Osaka University. It has been activated and became operational since 2009. Following the previous experiment with the PW laser, upgraded integrated experiments of fast ignition have been started using the LFEX laser with an energy up to 1 kJ in 2009 and 2 kJ in 2010 in a 1-5 ps 1.053 µm pulse. Experimental results including implosion of the shell target by Gekko-XII, heating of the imploded fuel core by LFEX laser injection, and increase of the neutron yield due to fast heating compared with no heating have been achieved. Results in the 2009 experiment indicated that the heating efficiency was 3-5%, much lower than the 20-30% expected from the previous 2002 data. It was attributed to the very hot electrons generated in a long scale length plasma in the cone preformed with a

100 TW light from the Petawatt Module (PWM) laser illuminated a preimploded spherical deuterated polystyrene(CD) shell target. The DD neutron yield increased from 2.5×105–106. Analysis indicates that hundreds of keV deuterons, generated around the critical density, collide with cold fuel deuterons and play the leading role in the enhancement of the neutron yield. A two-dimensional particle-in-cell (2D PIC) simulation predicted well the deuteron spectrum. A 60 TW laser was used for MeV proton emissions and megagauss magnetic fields generation on the rear surface of a Poly p-xylene(C8H8) plane target. The 2D PIC simulation explained well the results. The PWM laser was upgraded to one PW, making it the world biggest Petawatt laser (PW laser). An optically parametric chirped amplification was introduced in the front end. The pulse was synchronized to the GEKKO XII imploding beams to within 10 ps.

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