Fast ignition integrated experiments with Gekko and LFEX lasers

Abstract

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

Magnetically Assisted Fast Ignition

“…1(a) a cone is used with wall depth 5 μm, density 200n c , tip size 20 μm, and inner length 20 μm. The cone opening angle of 30°and the distance of 35 μm between the tip to target center approach the experimental parameters [3][4][5]. To allow for prepulse effects, a preplasma is taken inside the cone with an exponential profile with scale length 2 μm along the x direction (our simulation shows the laser-to-core coupling is reduced by 25% with the increased scale length 4 μm, and the coupling approaches the experimental result in [4]).…”

“…Up to 20% coupling from a 0.6 ps ignition laser was demonstrated experimentally in 2001 [2] with a coneinserted target to reduce the transport distance of the electrons to the core. However, a few subsequent experiments with longer duration ignition lasers between 2008 and 2011 reported much lower coupling at Vulcan [3], Omega EP [4], and GEKKO XII systems [5], respectively. The large difference in the coupling was not completely understood, but could be related to different preplasmas formed by the ignition laser prepulses in the cones [3][4][5].…”

“…However, a few subsequent experiments with longer duration ignition lasers between 2008 and 2011 reported much lower coupling at Vulcan [3], Omega EP [4], and GEKKO XII systems [5], respectively. The large difference in the coupling was not completely understood, but could be related to different preplasmas formed by the ignition laser prepulses in the cones [3][4][5]. A commonly cited factor causing the low coupling in these experiments [3][4][5] is large divergence of the fast electrons generated in the cones [6,7].…”

“…The large difference in the coupling was not completely understood, but could be related to different preplasmas formed by the ignition laser prepulses in the cones [3][4][5]. A commonly cited factor causing the low coupling in these experiments [3][4][5] is large divergence of the fast electrons generated in the cones [6,7]. Divergence angles up to 50°w…”

The Development of the Neutron Detector for the Fast Ignition Experiment by using LFEX and Gekko XII Facility

“…Especially, the world largest peta-watt laser "LFEX" with energy exceeding 1 kJ and 1 ps pulse duration is currently operated at the Institute of Laser Engineering (ILE), Osaka University. At the moment, this is a unique laser system, which parameters make it particularly attractive for application to FI studies [1]. However, diagnostics of the fusion neutron in the fast ignition is extremely difficult due to intense γ-ray generated from the heating laser.…”