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Title: Simulation and design study of cryogenic cone shell target for Fast Ignition Realization Experiment project

Abstract

In the fast ignition (FI) scheme, at first, high-density fuel core plasma is assembled by implosion laser, and is then heated by petawatt laser to achieve a fusion burning condition. The formation of high-density fuel core plasma is one of the key issues for FI. A typical target for FI is a shell fitted with a reentrant gold cone to make a pass for heating laser. The ablated plasma of gold cone interferes with the implosion dynamics, which is quite different from that of the conventional central-hot-spot approach. Therefore, the dynamics of a nonspherical implosion must be controlled to assemble high density and high areal density. Numerical simulations are performed to study radiation hydrodynamics of cone-guided implosions. In the results, the effect of the cone on implosion dynamics is clarified. The cone surface is irradiated by the radiation and ablated plasma affects the imploding shell. Coating on the cone, which tamps the gold plasma, is effective to improve the implosion performance, although the result does not satisfy the condition of core plasma for the first stage of the Fast Ignition Realization Experiment [K. Mima et al., Proceedings of the IAEA Fusion Energy Conference, Lyon, 2002 (IAEA, Vienna, 2002), Paper No.more » IAEA-CN-94/IF/03].« less

Authors:
; ; ; ; ;  [1];  [2];  [2];  [2]
  1. Institute of Laser Engineering, Osaka University, 2-6 Yamada-oka, Suita, Osaka 565-0871 (Japan)
  2. (Japan)
Publication Date:
OSTI Identifier:
20975061
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 14; Journal Issue: 5; Other Information: DOI: 10.1063/1.2671124; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; CONES; DENSITY; DESIGN; GOLD; HYDRODYNAMICS; IMPLOSIONS; LASERS; PETAWATT POWER RANGE; PLASMA; PLASMA HEATING; PLASMA SIMULATION; THERMONUCLEAR REACTORS

Citation Formats

Nagatomo, Hideo, Johzaki, Tomoyuki, Nakamura, Tatsufumi, Sakagami, Hitoshi, Sunahara, Atsushi, Mima, Kunioki, National Institute for Fusion Science, Oroshi-cho, Toki, Gifu 509-5292, Institute for Laser Technology, 2-6 Yamada-oka, Suita, Osaka 565-0871, and Institute of Laser Engineering, Osaka University, 2-6 Yamada-oka, Suita, Osaka 565-0871. Simulation and design study of cryogenic cone shell target for Fast Ignition Realization Experiment project. United States: N. p., 2007. Web. doi:10.1063/1.2671124.
Nagatomo, Hideo, Johzaki, Tomoyuki, Nakamura, Tatsufumi, Sakagami, Hitoshi, Sunahara, Atsushi, Mima, Kunioki, National Institute for Fusion Science, Oroshi-cho, Toki, Gifu 509-5292, Institute for Laser Technology, 2-6 Yamada-oka, Suita, Osaka 565-0871, & Institute of Laser Engineering, Osaka University, 2-6 Yamada-oka, Suita, Osaka 565-0871. Simulation and design study of cryogenic cone shell target for Fast Ignition Realization Experiment project. United States. doi:10.1063/1.2671124.
Nagatomo, Hideo, Johzaki, Tomoyuki, Nakamura, Tatsufumi, Sakagami, Hitoshi, Sunahara, Atsushi, Mima, Kunioki, National Institute for Fusion Science, Oroshi-cho, Toki, Gifu 509-5292, Institute for Laser Technology, 2-6 Yamada-oka, Suita, Osaka 565-0871, and Institute of Laser Engineering, Osaka University, 2-6 Yamada-oka, Suita, Osaka 565-0871. Tue . "Simulation and design study of cryogenic cone shell target for Fast Ignition Realization Experiment project". United States. doi:10.1063/1.2671124.
@article{osti_20975061,
title = {Simulation and design study of cryogenic cone shell target for Fast Ignition Realization Experiment project},
author = {Nagatomo, Hideo and Johzaki, Tomoyuki and Nakamura, Tatsufumi and Sakagami, Hitoshi and Sunahara, Atsushi and Mima, Kunioki and National Institute for Fusion Science, Oroshi-cho, Toki, Gifu 509-5292 and Institute for Laser Technology, 2-6 Yamada-oka, Suita, Osaka 565-0871 and Institute of Laser Engineering, Osaka University, 2-6 Yamada-oka, Suita, Osaka 565-0871},
abstractNote = {In the fast ignition (FI) scheme, at first, high-density fuel core plasma is assembled by implosion laser, and is then heated by petawatt laser to achieve a fusion burning condition. The formation of high-density fuel core plasma is one of the key issues for FI. A typical target for FI is a shell fitted with a reentrant gold cone to make a pass for heating laser. The ablated plasma of gold cone interferes with the implosion dynamics, which is quite different from that of the conventional central-hot-spot approach. Therefore, the dynamics of a nonspherical implosion must be controlled to assemble high density and high areal density. Numerical simulations are performed to study radiation hydrodynamics of cone-guided implosions. In the results, the effect of the cone on implosion dynamics is clarified. The cone surface is irradiated by the radiation and ablated plasma affects the imploding shell. Coating on the cone, which tamps the gold plasma, is effective to improve the implosion performance, although the result does not satisfy the condition of core plasma for the first stage of the Fast Ignition Realization Experiment [K. Mima et al., Proceedings of the IAEA Fusion Energy Conference, Lyon, 2002 (IAEA, Vienna, 2002), Paper No. IAEA-CN-94/IF/03].},
doi = {10.1063/1.2671124},
journal = {Physics of Plasmas},
number = 5,
volume = 14,
place = {United States},
year = {Tue May 15 00:00:00 EDT 2007},
month = {Tue May 15 00:00:00 EDT 2007}
}
  • Thermonuclear ignition and subsequent burn are key physics for achieving laser fusion. In fast ignition, a highly compressed fusion fuel generated with multiple ns-laser beams is rapidly heated with a large energy, ps-laser pulse in prior to core disassembly. This scheme has a high potential to achieve ignition and burn since driver energy required for high fusion gain is predicted to be about one tenth of that needed for the central ignition scheme. In Japan, Fast Ignition Realization Experiment (FIREX) project has been started to clarify the physics of energy transport and deposition in the core plasma and to demonstratemore » fuel temperature of above 5 keV. After the success, FIREX-I will be followed by the second phase of the project (FIREX-II) to demonstrate ignition and burn. LFEX laser, designed to deliver a laser pulse of 10 kJ in 10 ps, are operational and the first phase of FIREX experiments has been stated. A new target is proposed to attain dense compression of fuel and improve laser-core coupling efficiency by adopting double-cone structure, a low-density inner liner, low-Z outer coating, and Br-doped fuel shell. In this paper, present status and near term prospects of the FIREX-I project will be reported together with activities on target designing, laser development, and plasma diagnostics.« less
  • A petawatt laser for fast ignition experiments (LFEX) laser system [N. Miyanaga et al., J. Phys. IV France 133, 81 (2006)], which is currently capable of delivering 2 kJ in a 1.5 ps pulse using 4 laser beams, has been constructed beside the GEKKO-XII laser facility for demonstrating efficient fast heating of a dense plasma up to the ignition temperature under the auspices of the Fast Ignition Realization EXperiment (FIREX) project [H. Azechi et al., Nucl. Fusion 49, 104024 (2009)]. In the FIREX experiment, a cone is attached to a spherical target containing a fuel to prevent a corona plasma frommore » entering the path of the intense heating LFEX laser beams. The LFEX laser beams are focused at the tip of the cone to generate a relativistic electron beam (REB), which heats a dense fuel core generated by compression of a spherical deuterized plastic target induced by the GEKKO-XII laser beams. Recent studies indicate that the current heating efficiency is only 0.4%, and three requirements to achieve higher efficiency of the fast ignition (FI) scheme with the current GEKKO and LFEX systems have been identified: (i) reduction of the high energy tail of the REB; (ii) formation of a fuel core with high areal density using a limited number (twelve) of GEKKO-XII laser beams as well as a limited energy (4 kJ of 0.53-μm light in a 1.3 ns pulse); (iii) guiding and focusing of the REB to the fuel core. Laser–plasma interactions in a long-scale plasma generate electrons that are too energetic to efficiently heat the fuel core. Three actions were taken to meet the first requirement. First, the intensity contrast of the foot pulses to the main pulses of the LFEX was improved to >10{sup 9}. Second, a 5.5-mm-long cone was introduced to reduce pre-heating of the inner cone wall caused by illumination of the unconverted 1.053-μm light of implosion beam (GEKKO-XII). Third, the outside of the cone wall was coated with a 40-μm plastic layer to protect it from the pressure caused by imploding plasma. Following the above improvements, conversion of 13% of the LFEX laser energy to a low energy portion of the REB, whose slope temperature is 0.7 MeV, which is close to the ponderomotive scaling value, was achieved. To meet the second requirement, the compression of a solid spherical ball with a diameter of 200-μm to form a dense core with an areal density of ∼0.07 g/cm{sup 2} was induced by a laser-driven spherically converging shock wave. Converging shock compression is more hydrodynamically stable compared to shell implosion, while a hot spot cannot be generated with a solid ball target. Solid ball compression is preferable also for compressing an external magnetic field to collimate the REB to the fuel core, due to the relatively small magnetic Reynolds number of the shock compressed region. To meet the third requirement, we have generated a strong kilo-tesla magnetic field using a laser-driven capacitor-coil target. The strength and time history of the magnetic field were characterized with proton deflectometry and a B-dot probe. Guidance of the REB using a 0.6-kT field in a planar geometry has been demonstrated at the LULI 2000 laser facility. In a realistic FI scenario, a magnetic mirror is formed between the REB generation point and the fuel core. The effects of the strong magnetic field on not only REB transport but also plasma compression were studied using numerical simulations. According to the transport calculations, the heating efficiency can be improved from 0.4% to 4% by the GEKKO and LFEX laser system by meeting the three requirements described above. This efficiency is scalable to 10% of the heating efficiency by increasing the areal density of the fuel core.« less
  • Electron energy characteristics generated by the irradiation of ultraintense laser pulses onto solid targets are controlled by using cone targets. Two parameters characterizing the laser-cone interaction are introduced, which are cone angle and the ratio of the laser spot size to the cone tip size. By changing these parameters, the energy absorption rate, laser irradiance at the cone tip, and electron acceleration at the cone tip and side wall are controlled. The optimum cone targets for fast ignition are 30 deg. cone angle with double-cone geometry, and a tip size comparable to the core size, with the irradiation of amore » laser pulse with a spot size of about four times the cone tip size. Cone targets have the possibility to enhance the maximum energy of laser-accelerated protons by using a smaller angle cone depending on the laser f-number.« less
  • Fast ignition is a two-step inertial confinement fusion concept where megaelectron volt electrons ignite the compressed core of an imploded fuel capsule driven by a relatively low-implosion velocity. Initial surrogate cone-in-shell, fast-ignitor experiments using a highly shaped driver pulse to assemble a dense core in front of the cone tip were performed on the OMEGA/OMEGA EP Laser [T. R. Boehly et al., Opt. Commun. 133, 495 (1997); L. J. Waxer et al., Opt. Photonics News 16, 30 (2005)]. With optimal timing, the OMEGA EP pulse produced up to {approx}1.4 x 10{sup 7} additional neutrons which is a factor of {approx}4more » more neutrons than without short-pulse heating. Shock-breakout measurements performed with the same targets and drive conditions demonstrate an intact cone tip at the time when the additional neutrons are produced. Velocity interferometer system for any reflector measurements show that x-rays from the shell's coronal plasma preheat the inner cone wall of thin-walled Au cones, while the thick-walled cones that are used in the integrated experiments are not affected by preheat.« less
  • Measurements of energetic protons from cone-in-shell fast-igniton implosions at Omega have been conducted. In these experiments, charged-particle spectrometers were used to measure a significant population (>10{sup 13}) of energetic protons (7.5 MeV max.), indicating the presence of strong electric fields. These energetic protons, observed in directions both transverse and forward relative to the direction of the short-pulse laser beam, have been used to study aspects of coupling efficiency of the petawatt fast-ignitior beam. Approximately 5% of the laser energy coupled to hot electrons was lost to fast ions. Forward going protons were less energetic and showed no dependence on lasermore » intensity or whether the cone tip was intact when the short-pulse laser was fired. Maximum energies of protons emitted transverse to the cone-in-shell target scale with incident on-target laser intensity (2-6 Multiplication-Sign 10{sup 18}W-cm{sup -2}), as described by the ponderomotive scaling ({proportional_to}I{sup 1/2}). It is shown that these protons are accelerated from the entire cone, rather than from the cone tip alone. These protons were used to estimate the lower limit on the hot-electron temperature, which was found to be hotter than the ponderomotive scaling by factors of 2-3.« less