Petapascal Pressure Driven by Fast Isochoric Heating with a Multipicosecond Intense Laser Pulse

Abstract

Fast isochoric laser heating is a scheme to heat a matter with relativistic-intensity (> 10 18 W/cm 2 ) laser pulse or X-ray free electron laser pulse. The fast isochoric laser heating has been studied for creating efficiently ultra-high-energy-density (UHED) state. We demonstrate an fast isochoric heating of an imploded dense plasma using a multi-picosecond kJ-class petawatt laser with an assistance of externally applied kilo-tesla magnetic fields for guiding fast electrons to the dense plasma.The UHED state with 2.2 Peta-Pascal is achieved experimentally with 4.6 kJ of total laser energy that is one order of magnitude lower than the energy used in the conventional implosion scheme. A two-dimensional particle-in-cell simulation reveals that diffusive heating from a laserplasma interaction zone to the dense plasma plays an essential role to the efficient creation of the UHED state.Power laser apparatus can inject a plenty of energy to a matter in a small volume within a short time duration. The matter becomes a high-energy-density state that is applicable to various scientific researches such as laboratory astrophysics [1] and several kind of radiation sources: X-rays, charged particles, and neutrons [2,3]. Fast isochoric heating of solid target to create such highenergy-density states have been demonstrated by short pulse laser [4] and X-ray free electron laser [5,6]. The fast isochoric laser heating of imploded plasma is one of the scheme to create ultra-high-energy-density (UHED) state, which is equivalent to the state at the center of the sun, for the inertial confinement fusion (ICF) science.In conventional implosion, kinetic energy of the imploded shell is converted to the internal energy of the compressed matter at the maximum compression. A UHED state with 36 Peta-Pascal (PPa) was achieved on the National Ignition Facility with 1.8 MJ of laser energy by the indirect X-ray driven implosion [7]. The OMEGA laser facility with 30 kJ of laser energy produced 5.6 PPa of UHED by the direct laser-driven implosion [8]. The current central ignition scheme requires enormous laser energy to create UHED state. The significant growth of hydrodynamic instabilities during the compression causes the hot spark mixing with the cold dense fuel and prevents efficient creation of UHED state.In the context of ICF, the fast isochoric heating also known as the fast ignition had been proposed as an alternative approach [9]. This approach separates compres-sion and heating processes to avoid the mixing, using a more stable compression followed by an external energy injection whose time scale is much shorter than the implosion time scale. Hence, it potentially leads to higher gain by increasing the mass of the compressed fuel .A cone-in-shell target is commonly used in the integrated fast-isochoric-heating experiments, since a dense plasma core, which is produced by the laser-driven implosion, is surrounded by a long-scale-length coronal plasma. The cone preserves a vacuum channel in the coronal plasma for the heating laser pulse to...

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

“…Using a GXII-precompressed solid ball with a cone and LFEX of 625 J, Sakata et al, had reported that the maximum laser-to-core coupling efficiency by drag heating is 7.7% ± 1.2% [25,26]. The core density, ρ, was simulated to be 11.3 g cm −3 .…”

Isochoric heating of solid-density plasmas beyond keV temperature by fast thermal diffusion with relativistic picosecond laser light

“…The experimental and simulation results of Ref. [15] suggest that the thermal diffusion from the hot preformed plasma region, where the laser light is stopped [16] and absorbed, contributes to the core heating in addition to the REBs. The required timescale of the transition of the dominant heating mechanism from the REB to thermal diffusion is a few picoseconds [17].…”

“…More recently, picosecond (ps) petawatt (PW) lasers, such as LFEX [14], have become accessible. Matsuo et al applied the LFEX laser to heat the imploded * higashi@eng.hokudai.ac.jp core and achieved an electron temperature of approximately 2 keV at the core region with an energy density of 2 PPa [15]. This highly efficient heating is difficult to be explained only by REBs.…”

Fabrication of high-concentration Cu-doped deuterated targets for fast ignition experiments

“…In FI, understanding the mechanisms of energy transfer from fast electrons to the compressed plasma core is critical for efficient fusion fuel heating. In various experiments [3][4][5][6][7][8][9][10][11][12][13][14][15] characteristic x-rays produced by the laser-accelerated fast electrons were utilized to understand the mechanisms of electron transport in dense plasma, and neutrons generated during IFE experiments have been utilized to investigate the fusion reaction as well as the temperature of the compressed core. Characteristic x-rays and neutrons are measured using fuel targets containing tracer atoms that generate a specific signal during a fusion reaction in IFE experiments.…”