High Gain ICF Research Articles

Pulse heating and ignition for off-centre ignited targets

An off-centre ignition model has been used to study the ignition conditions for laser targets related to the fast ignition scheme. A 2-D hydrodynamic code has been used, including alpha particle heating. The main goal of the study is the possibility of obtaining a high gain ICF target with fast ignition. In order to determine the ignition conditions, samples with various compressed core densities having different spark density-radius product (i.e. areal density) values were selected. The study was carried out in the presence of an external heating source, with a constant heating rate. A dependence of the ignition conditions on the heating rate of the external pulse is demonstrated. For a given set of ignition conditions, our simulation showed that an 11 ps pulse with 17 kJ of injected energy into the spark area was required to achieve ignition for a compressed core with a density of 200 g/cm3 and 0.5 g/cm2 spark areal density. It is shown that the ignition conditions are highly dependent on the heating rate of the external pulse.

Numerical Simulation of the Explosion Dynamics and Energy Release from High-Gain ICF Targets

Results from numerical simulations are presented describing the explosion energetics of a high-gain indirect-drive ICF target. The light ion fusion LIBRA-SP target, which consists of an x-ray driven capsule embedded in a spherical foam-filled hohlraum, is imploded using 12 prepulse and 12 full power Li beams containing a total energy of 8 MJ. Here, we report on the dynamics of the target energy release, focussing in particular on the partitioning of energy between x rays, neutrons, and target debris kinetic energy. Our results indicate that 72% and 22% of the 552 MJ yield is emitted by the target in the form of neutrons and x-rays, respectively. Calculated emergent spectra for the target neutrons and x rays are also presented. 12 refs., 5 figs., 1 tab.

Radiation Transport Effects in the Target Chamber Gas of the Laser Fusion Power Reactor SIRIUS-P

The authors present results from radiation-hydrodynamics calculations which show the central role resonant self-absorption plays in reducing radiative energy loss rates in high-gain ICF target chamber plasmas. Calculations were performed using a non-LTE radiative transfer model which they have recently coupled to their target chamber radiation-hydrodynamics code. The lower radiation fluxes escaping the plasma, which occur due to the self-absorption of line radiation in their optically thick cores, lead to significantly lower temperature increases at the surface of the target chamber first wall. The calculations were performed for the SIRIUS-P laser-driven direct-drive ICF power reactor. In this conceptual design study, high-gain targets release approximately 400 MJ of energy in the center of a gas-filled target chamber. The target debris ions and x-rays are stopped in the gas, and the energy is reradiated to the chamber wall over a much longer time scale. Because the time scales are comparable to the time it takes to thermally conduct energy away from the first surface, the thermal stresses and erosion rates for the first wall are greatly reduced.

Rayleigh-Taylor instability study for heavy-ion beam driven, high-gain ICF implosions

We carried out a numerical analysis on the stability of targets designed to produce fusion energy gains close to 100 when irradiated with an appropriate heavy ion beam. To reach such performances, we found that a high-Z radiation shield was necessary to screen the DT fuel from the radiation coming from the surrounding hot material. As opacity of high-Z materials is only weakly density dependent, we considered targets with lead shields both at solid density and with a density equivalent to that of the contiguous external material. The behaviour of both kinds of targets has been studied by introducing a small spatial nonuniformity on the external surface of the lead shield. Targets with low-density shields have been tested with a beam intensity perturbation, too. Because density gradients are very sharp and ablation is practically absent, we have found these implosions to be Rayleigh-Taylor unstable. The evolution has been followed in the nonlinear regime because the full hydrodynamical-radiative model with a nonlinear heavy ion energy deposition and mesh correction was used.

Progress on Achieving the ICF Conditions Needed for High Gain

Progress during the past two years has moved us much closer to demonstrating the scientific and technological requirements for high gain ICF in the laboratory. This progress has been made possible by operating at the third harmonic of lym light which dramatically reduces concern about hot electrons and by advances in diagnostics such as 100 ps x-ray framing cameras which greatly increase the data available from each experiment. Making use of many of these new capabilities, major improvements in confinement conditions have been achieved for ICF implosions. In particular, in an optimized hohlraum on Nova, radiation driven implosions with convergence ratio in excess of 30 (volume compression ∼3 × 104) have performed essentially as predicted by spherical implosion calculations. This paper presents these results as well as examples of advances in several other areas and discusses the implications for the future of ICF with lasers and heavy ion beam drivers.

Overview of the ICF 1000 MJ Experiment Chamber Design

A conceptual design of an experiment chamber for a high gain ICF facility (1000 MJ) is being developed. Performance goals have been established. Several design approaches are being evaluated through computer simulations, engineering analysis, and experimental testing of candidate first wall components.

Final Optic Protection Designs for ICF Containment Chambers

The output from a laser-driven high-gain ICF target in the laboratory microfusion facility (LMF) target chamber could produce enough x-rays, shrapnel, and debris to severely damage the laser’s final optics. If the final optics were left unprotected, the replacement and reinstallation costs for each beam would exceed $40K. Assuming the laser has 68 beams, the replacement costs for each shot could reach $2.7M. To avoid these excessive costs, we must design a reliable optics protection system. This requires that we define the hazardous environment to which the optics are exposed.Thegeometrical layout for the 68 beams of the 10 megajoule laser shows the final optics placed at 25 meters from the target (see Fig. 1). The final optic will be a 2–5 cm thick debris shield ($40K each) which will be placed in front of a $200K focussing lens. Each of the 68 beams will deliver 150 kJ of 0.35 µm (3ω) light and will consist of either a 4×4 or a 2×8 array of beamlets, with each beamlet aperture having dimensions of 29 cm × 29 cm. This produces a 3ω energy density at the final optic of 12 J/cm2 average and 225-30 J/cm2 peak.

Design Issues for a Light Ion Beam LMF Driver

The U.S. Department of Energy is conducting a preliminary study of a Laboratory Microfusion Facility (LMF). A major goal of the LMF is the development of high-gain ICF targets in a laboratory envir...

High-gain, low-intensity ICF targets for a charged-particle beam fusion driver

A class of high-gain ICF targets driven by electrons or light ions is discussed. The targets are characterized by a low-beam-intensity requirement and large size. A magnetic field provides thermal insulation of pre-heated, low-density fuel. The addition of a cryogenic fuel layer increases the gain without requiring significantly increased beam power and intensity. The higher fuel adiabat and reduced fuel losses produce ignition and burn for lower implosion velocities and at lower power and intensity than conventional ablative designs. Gains of 20 to 40 are expected for intensities of ⪅ 80 TW·cm−2, initial magnetic fields of ⪆ 30–60 kG, an initial fuel radius of 0.2–0.4 cm, and irradiation uniformities of 6–7%. Driver requirements are ⪅ 45 TW·cm−2 if the initial magnetic field is ⪆ 300–600 kG, sufficient for alpha trapping in the compressed low-density fuel. Voltage shaping increases fuel burn-up and target ρr and lowers power and intensity levels by an additional factor of about 0.6.