Direct fast heating efficiency of a counter-imploded core plasma employing a laser for fast ignition experiments (LFEX)

Abstract

This study investigates the efficiency of the fast heating when a preimploded core is directly heated with an ultraintense laser(a heating laser). The efficiency is defined as an increment of internal core energy divided by heating laser energy on target. Six counterbeams from the GEKKO XII (GXII) green laser at the Institute of Laser Engineering (ILE), Osaka University, of which the output was 1.6kJ, imploded a spherical CD (Deuterated polystyrene) shell target and formed a dense core. DD-reacted protons and the x-ray core emissions showed a core density of 2.8 ∼ 2.7g/cm3. DD-reacted thermal neutrons were used to estimate the core temperature determined as 650 ∼ 750 eV. The core was then directly heated by a laser for fast-ignition experiments (LFEX), an extremely energetic ultrashort pulse laser at the ILE either with its axis lying to the GXII bundle axis, or with its axis perpendicular to the GXII bundle axis. We call the former laser configuration “Axial mode”, and the latter “Transverse mode”. η is 2% or less for Axial mode and 6% or less for Transverse mode. The efficiencies were compared to that of a uniform implosion mode, which was 3%.

Diagnosing the fast-heating process of the double-cone ignition scheme with x-ray spectroscopy

“…In the fast ignition scheme, ultra-intense laser pulses are utilized to generate a relativistic electron beam (REB), injecting into the pre-compressed isochoric plasma. The REB then travels forward as a strong current, heating the high-density fuel to generated a hot spot [4][5][6][7][8]. Research conducted over the past few decades has demonstrated that a guiding cone for heating could enhance efficiency by reducing the distance from the source to the core.…”