J. Breil

Compression phase study of the HiPER baseline target

The European High Power laser Energy Research (HiPER) project aims at demonstrating the feasibility of high gain inertial confinement fusion using the fast ignitor approach. A baseline target has been recently developed by Atzeni et al (2007 Phys. Plasmas 14 052702). We study here the robustness of this target during the compression phase and define pulse shape tolerances for a successful fuel assembly. The comparison between a standard and a relaxation pulse shows that the latter allows one to reduce both the laser power contrast and the growth of perturbations due to Rayleigh?Taylor instability. We have found that with 95?kJ of absorbed laser energy one can assemble the fuel with a peak density around 500?g?cm?2 and a peak areal density of 1.2?g?cm?2. This implies a total target gain of about 60.

Studies on targets for inertial fusion ignition demonstration at the HiPER facility

Recently, a European collaboration has proposed the High Power Laser Energy Research (HiPER) facility, with the primary goal of demonstrating laser driven inertial fusion fast ignition. HiPER is expected to provide 250u2009kJ in multiple, 3ω (wavelength λ = 0.35u2009µm), nanosecond beams for compression and 70u2009kJ in 10–20u2009ps, 2ω beams for ignition. The baseline approach is fast ignition by laser-accelerated fast electrons; cones are considered as a means to maximize ignition laser–fuel coupling. Earlier studies led to the identification of an all-DT shell, with a total mass of about 0.6u2009mg as a reference target concept. The HiPER main pulse can compress the fuel to a peak density above 500u2009gu2009cm−3 and an areal density ρR of about 1.5u2009gu2009cm−2. Ignition of the compressed fuel requires that relativistic electrons deposit about 20u2009kJ in a volume of radius of about 15u2009µm and a depth of less than 1.2u2009gu2009cm−2. The ignited target releases about 13u2009MJ. In this paper, additional analyses of this target are reported. An optimal irradiation pattern has been identified. The effects on fuel compression of the low-mode irradiation non-uniformities have been studied by 2D simulations and an analytical model. The scaling of the electron beam energy required for ignition (versus electron kinetic energy) has been determined by 2D fluid simulations including a 3D Monte Carlo treatment of relativistic electrons, and agrees with a simple model. Integrated simulations show that beam-induced magnetic fields can reduce beam divergence. As an alternative scheme, shock ignition is studied. 2D simulations have addressed optimization of shock timing and absorbed power, means to increase laser absorption efficiency and the interaction of the igniting shocks with a deformed fuel shell.

Self-consistent modeling of jet formation process in the nanosecond laser pulse regime

Laser induced forward transfer (LIFT) is a direct printing technique. Because of its high application potential, interest continues to increase. LIFT is routinely used in printing, spray generation and thermal-spike sputtering. Biological material such as cells and proteins have already been transferred successfully for the creation of biological microarrays. Recently, modeling has been used to explain parts of the ejection transfer process. No global modeling strategy is currently available. In this paper, a hydrodynamic code is utilized to model the jet formation process and estimate the constraints obeyed by the bioelements during the transfer. A self-consistent model that includes laser energy absorption, plasma formation via ablation, and hydrodynamic processes is proposed and confirmed with experimental results. Fundamental physical mechanisms via one-dimensional modeling are presented. Two-dimensional (2D) simplified solutions of the jet formation model equations are proposed. Predicted results of the model are jet existence and its velocity. The 2D simulation results are in good agreement with a simple model presented by a previous investigator.

Analytic criteria for shock ignition of fusion reactions in a central hot spot

Shock ignition is an inertial confinement fusion scheme where the ignition conditions are achieved in two steps. First, the DT shell is compressed at a low implosion velocity creating a central core at a low temperature and a high density. Then, a strong spherical converging shock is launched before the fuel stagnation time. It increases the central pressure and ignites the core. It is shown in this paper that this latter phase can be described analytically by using a self-similar solution to the equations of ideal hydrodynamics. A high and uniformly distributed pressure in the hot spot can be created thus providing favorable conditions for ignition. Analytic ignition criteria are obtained that relate the areal density of the compressed core with the shock velocity. The conclusions of the analytical model are confirmed in full hydrodynamic simulations.

Studying ignition schemes on European laser facilities

Demonstrating ignition and net energy gain in the near future on MJ-class laser facilities will be a major step towards determining the feasibility of Inertial Fusion Energy (IFE), in Europe as in the United States. The current status of the French Laser MegaJoule (LMJ) programme, from the laser facility construction to the indirectly driven central ignition target design, is presented, as well as validating experimental campaigns, conducted, as part of this programme, on various laser facilities. However, the viability of the IFE approach strongly depends on our ability to address the salient questions related to efficiency of the target design and laser driver performances. In the overall framework of the European HiPER project, two alternative schemes both relying on decoupling target compression and fuel heating—fast ignition (FI) and shock ignition (SI)—are currently considered. After a brief presentation of the HiPER projects objectives, FI and SI target designs are discussed. Theoretical analysis and 2D simulations will help to understand the unresolved key issues of the two schemes. Finally, the on-going European experimental effort to demonstrate their viability on currently operated laser facilities is described.

Dynamics and structure of self-generated magnetics fields on solids following high contrast, high intensity laser irradiation

The dynamics of self-generated magnetic B-fields produced following the interaction of a high contrast, high intensity (Iu2009>u20091019u2009W cm−2) laser beam with thin (3u2009μm thick) solid (Al or Au) targets is investigated experimentally and numerically. Two main sources drive the growth of B-fields on the target surfaces. B-fields are first driven by laser-generated hot electron currents that relax over ∼10–20 ps. Over longer timescales, the hydrodynamic expansion of the bulk of the target into vacuum also generates B-field induced by non-collinear gradients of density and temperature. The laser irradiation of the target front side strongly localizes the energy deposition at the target front, in contrast to the target rear side, which is heated by fast electrons over a much larger area. This induces an asymmetry in the hydrodynamic expansion between the front and rear target surfaces, and consequently the associated B-fields are found strongly asymmetric. The sole long-lasting (>30 ps) B-fields are the ones growing...

A compact broadband ion beam focusing device based on laser-driven megagauss thermoelectric magnetic fields

Ultra-intense lasers can nowadays routinely accelerate kiloampere ion beams. These unique sources of particle beams could impact many societal (e.g., proton-therapy or fuel recycling) and fundamental (e.g., neutron probing) domains. However, this requires overcoming the beam angular divergence at the source. This has been attempted, either with large-scale conventional setups or with compact plasma techniques that however have the restriction of short (<1 mm) focusing distances or a chromatic behavior. Here, we show that exploiting laser-triggered, long-lasting (>50 ps), thermoelectric multi-megagauss surface magnetic (B)-fields, compact capturing, and focusing of a diverging laser-driven multi-MeV ion beam can be achieved over a wide range of ion energies in the limit of a 5° acceptance angle.

Shock generation comparison with planar and hemispherical targets in shock ignition relevant experiment

We performed an experiment on the “Ligne dIntegration Laser” facility to produce strong shocks with plasma conditions relevant for the Shock Ignition approach to Inertial Confinement Fusion. Two kinds of targets have been used: planar and hemispherical. We observe an increase in the shock velocity in hemispherical geometry, which entails a fairly planar shock despite the Gaussian focal spot. Numerical results reproduce the shock dynamics in the two cases in a successful way, indicating, for laser intensities around 1.5u2009×u20091015u2009W/cm2 at 3ω, an ablation pressure of (90u2009±u200920) Mbar and (120u2009±u200920) Mbar in planar and hemispherical geometry, respectively.

Toward a new nanoLIFT transfer process

The Laser Induced Forward Transfer (LIFT) is a direct‐write technique used to print biological materials such as living cells or molecules. During the LIFT process, the biomaterial to be printed is deposited on a target submitted to a nanosecond laser shot, and the ejecta are collected onto a receiving substrate. Despite the several advantages of this technique (control of the propelled quantity, no spoiling of the substrate), it remains difficult to be employed due to the high sensitivity of its control parameters. Recently, Duocastella published some experimental results which exhibit the real‐time jet formation process, under conditions similar to those present in the LIFT process [1].In the first Section, a typical experimental setup for LIFT process is presented. Then, simulations of Duocastella’s and Guillemot’s [2] experiments are carried out to model the jet formation in water when irradiated by an ultraviolet nanosecond laser pulse. The 2D axisymmetric hydrodynamic code CHIC (Code dHydrodynamiqu...