Target Fabrication Research Articles

Point design targets, specifications, and requirements for the 2010 ignition campaign on the National Ignition Facility

Point design targets have been specified for the initial ignition campaign on the National Ignition Facility [G. H. Miller, E. I. Moses, and C. R. Wuest, Opt. Eng. 443, 2841 (2004)]. The targets contain D-T fusion fuel in an ablator of either CH with Ge doping, or Be with Cu. These shells are imploded in a U or Au hohlraum with a peak radiation temperature set between 270 and 300 eV. Considerations determining the point design include laser-plasma interactions, hydrodynamic instabilities, laser operations, and target fabrication. Simulations were used to evaluate choices, and to define requirements and specifications. Simulation techniques and their experimental validation are summarized. Simulations were used to estimate the sensitivity of target performance to uncertainties and variations in experimental conditions. A formalism is described that evaluates margin for ignition, summarized in a parameter the Ignition Threshold Factor (ITF). Uncertainty and shot-to-shot variability in ITF are evaluated, and sensitivity of the margin to characteristics of the experiment. The formalism is used to estimate probability of ignition. The ignition experiment will be preceded with an experimental campaign that determines features of the design that cannot be defined with simulations alone. The requirements for this campaign are summarized. Requirements are summarized for the laser and target fabrication.

Fabrication of thin self-supporting platinum targets using evaporation techniques

Thin self-supporting isotopic platinum (Pt) targets of 130–200 μg/cm 2 thickness have been prepared by evaporation technique, using selective etching and parting reagent methods. The evaporation yield of the selective etching method was higher in comparison to the parting reagent method. Further, the purity of targets formed has been accessed by the Energy Dispersive X-ray Fluorescence (EDXRF) and Elastic Recoil Detection Analysis (ERDA) techniques. The analysis indicated that the targets prepared by the selective etching method contain 2 wt% of Cu. Contamination of C was found to be 2.5 wt% in the targets prepared by both of these methods.

Target Fabrication at the University of Michigan

At the University of Michigan (U-M), we have successfully fabricated and characterized targets for our experimental campaigns since 2003. Because of the unique production environment, we iterate many models in the course of a single-shot plan and have the flexibility to test and alter target designs as needed throughout the build process. Over the past few years, many advances in target design and fabrication have allowed greater degrees of design complexity while retaining the high level of build precision necessary for microscale experiments on facilities such as the OMEGA laser. Extensive target metrology is carried out during and after the fabrication process to allow for full knowledge of experimental conditions and to ensure that all targets are within required specifications. Analysis of the variability in metrology measurements over the multiple-shot campaigns allows for the quantification of improvements in the target build quality and metrology measurements. We present a summary of the capabilities and recent developments of target fabrication at U-M, as well as progress and analysis of build repeatability.

On-Chip Double Emulsion Droplet Assembly Using Electrowetting-on-Dielectric and Dielectrophoresis

The double emulsion (DE) droplets used for fabrication of cryogenic foam targets for inertial confinement fusion experiments require precisely controlled volumes. On-chip electric field actuated microfluidic assembly of DE droplets can be used to achieve such precision. The electrowetting-on-dielectric and dielectrophoresis effects make it possible to manipulate both conductive and dielectric droplets simultaneously on a substrate. Aqueous and nonaqueous liquid droplets precisely dispensed from two reservoirs on a microfluidic chip are transported and combined to form oil-in-water-in-air or water-in-oil-in-air DE droplets. The dispensing reproducibility is studied as a function of a set of operation parameters. Conditions for spontaneous emulsification for DE formation are developed in terms of droplet surface energies.

Fabrication of Backlighter Laser Targets via Lithography

Lithographed wire targets have recently been fabricated for use as backlighter targets for experimental campaigns at the OMEGA laser facility. These experiments required targets with 10-μm gold wires lithographed onto plastic. A process was developed using lithography to make these targets via sputter coating and liquid solution removal of the resist. One of the challenges overcome in developing this target was depositing the gold so that it would strongly adhere to the plastic. The quality of the lithographed targets was much better than targets made by other methods, such as gluing or thermal techniques. The lithographed targets were straighter, which is important in order to minimize the emission spot size at shot time. The lithographed targets also did not have problems with plastic or glue covering the wires, which can also reduce target emission, another challenge for gluing or thermal techniques. Lithography also allows a large number of similar targets to be made at once and cut out to the individual size needed, and a wide range of complex patterns or designs are possible using this technique.

An Update of Target Fabrication Techniques for the Mass Production of Advanced Fast Ignition Cone Targets

The United States and France are constructing multi-billion-dollar laser facilities to demonstrate inertial fusion as a potential source of energy for the future. These facilities aim to use the inertial confinement fusion scheme to demonstrate ignition on the 2010-2012 timescale. The recently launched High Power Laser Energy Research facility (HiPER) project is a European initiative to offer a credible way to build upon this work and demonstrate the possibility of opening up inertial fusion energy as a commercial process for energy generation. These facilities pose huge engineering and scientific challenges not only in their design but also in the technical challenges of providing the targets that will contain the fuel required to run them. We review the current manufacturing techniques of the cone target component as well as the work toward mass production of this component.

Target Fabrication of Opacity Experiments on Z for Weapons Science Applications

Opacity data are very important in high energy density physics experiments. Recent targets of alternating layers of either Al2Te3 or Mg/Sn with a CH tamper have been made for obtaining these data. These targets are geometrically simple in the half-moon configuration of the metal compound coating to the pure CH tamper but require stringent procedural requirements to fabricate to the purity requirements. These specific targets require mass ratios of elements that proved to be difficult to obtain while also having the requirement of being pinhole-free and oxygen-free.

NIF Ignition Target Requirements, Margins, and Uncertainties: Status February 2010

Targets intended to produce ignition on the National Ignition Facility (NIF) are being simulated, and the simulations are used to set specifications for target fabrication. Recent design work has focused on incorporating the implications of NIF experiments that were done in fall 2009 and planning for the campaign in 2010. Near-term experiments will use Ge-doped CH, although Be and diamond are still under active consideration for 2011 and beyond. The emphasis in this paper will be on changes in the requirements over the last year, the characteristics of the 2010 CH-ablator design, and the designs for 2011 and beyond. Capsule defects of particular interest are surface perturbations on the CH ablator and composition variations in the Be shells. Complete tables of specifications are regularly updated for all of the targets. All the specifications are rolled together into an error budget indicating adequate margin for ignition with all of the designs.

Status of the Development of the HiPER Single-Shot Target

The High Power laser Energy Research facility (HiPER) is a European project dedicated to demonstrating the feasibility of producing energy by laser-driven inertial confinement fusion. A first design of the fast ignition cryogenic target has been established. It is composed of a thin-walled microshell with an inserted gold cone and filled with deuterium-tritium (DT) fuel by means of a capillary (conically guided capsule). After assembly, targets must be tight at cryogenic temperatures (16 to 19.6 K).In order to evaluate the manufacturing feasibility of a single-shot target prototype, a program has been adapted from the Laser Mégajoule (LMJ) cryogenic target fabrication know-how. Target component study for HiPER concerns a hollow gold cone (25-deg half-angle and ˜25-μm thickness), a thin polymeric microshell (2-mm diameter and 3- to 10-μm thickness), and a silica capillary (30-μm outer diameter).First gas-tight targets at 77 K have been produced (helium gas leak rate ˜1.4 × 10-11 Pa·m3/s). Major efforts have been focused on thin-walled microshells, robust gold cone fabrication, and target assembly (minimizing of the glue quantity as well as helium gas leak tests) and will be discussed in this paper.

Laser targets and experiments for the sake of science and energy in the 22nd century

Laser fusion for energy and hybride schemes with laser application are original and highly tempting because they are ecofriendly, with almost unlimited resources. Though quite challenging, even development stage is fruitful in hi-tech and provides vast fundamental knowledge. The present paper discusses important results concerning target fabrication detailing several finer points of view which may not appear obvious. The current status of and achievements in targets are provided and validation experiments are discussed. The prospects and the unexpected difficulties are presented. The comparable resources and cost (unlike sizes differing orders of magnitude) for the targets and for driver over the driver’s life cycle scale prove there is no time to waste with target technology findings and validation experiments, especially in view of ignition shortly expected with National Ignition Facility.

Fabrication and Performance of Al-NaI Radioactive Transmutation Targets

Al-NaI radioactive transmutation target was prepared by powder metallurgy. The existing way of the phase of target was analyzed by the application of XRD and its microstructure and morphology was observed by SEM. Then EDS was used for micro-area energy spectrum analysis and the property of target with different NaI was measured and compared. The results show that NaI is uniformly distributed within the aluminum matrix. The relative density and bending strength of transmutation targets decrease with the increasing content of NaI. The hardness and electrical resistivity of transmutation targets increase with the increasing content of NaI.

Improvements in ICF target fabrication through high precision assembly and nondestructive characterization

Current ICF and HED targets are fielded on Omega, Z, and Trident; future campaigns will also be fielded on NIF. NIF will field less than 2 shots per day. With such few experiments, target fabrication and alignment accuracy, enhanced metrology and advanced component machining will be even more important. Future target designs are also becoming more complex and more stringent in terms of both manufacturing accuracy and precision. Several steps have been taken to improve the fabrication and characterization of targets, such as instituting an automated assembly station with 3 μm tolerances, utilizing non-destructive characterization tools for rapid component metrology and target assembly, and advancing machining capabilities. Recapitalization of target fabrication infrastructure is continuous.

Laser machining for fabrication of targets used in the FIREX-I project

This paper reports on way to fabricate a gas-tight targets dedicated for the first stage of Fast Ignition Realization Experiment (FIREX-I) at the Institute of Laser Engineering (ILE), Osaka University. It was found that a Ti;sapphire laser machining can be used to fabricate the target. The performance of the laser machining using a fs Ti;sapphire laser was examined on shell materials. The conditions for accurate machining were determined. Michelson interferometer with two different wavelengths which imitates a white light interferometer is an excellent tool for confirming the gas-tightness of the target after assembly.

Energetic electron and ion generation from interactions of intense laser pulses with laser machined conical targets

The generation of energetic electron and proton beams was studied from the interaction of high intensity laser pulses with pre-drilled conical targets. These conical targets are laser machined onto flat targets using 7–180 µJ pulses whose axis of propagation is identical to that of the main high intensity pulse. This method significantly relaxes requirements for alignment of conical targets in systematic experimental investigations and also reduces the cost of target fabrication. These experiments showed that conical targets increase the electron beam charge by up to 44 ± 18% compared with flat targets. We also found greater electron beam divergence for conical targets than for flat targets, which was due to escaping electrons from the surface of the cone wall into the surrounding solid target region. In addition, the experiments showed similar maximum proton energies for both targets since the larger electron beam divergence balances the increase in electron beam charge for conical targets. 2D particle in cell simulations were consistent with the experimental results. Simulations for conical target without preplasma showed higher energy gain for heavy ions due to ‘directed coulomb explosion’. This may be useful for medical applications or for ion beam fast ignition fusion.

The Science and Technologies for Fusion Energy With Lasers and Direct-Drive Targets

We are carrying out a multidisciplinary multi-institutional program to develop the scientific and technical basis for inertial fusion energy (IFE) based on laser drivers and direct-drive targets. The key components are developed as an integrated system, linking the science, technology, and final application of a 1000-MWe pure-fusion power plant. The science and technologies developed here are flexible enough to be applied to other size systems. The scientific justification for this work is a family of target designs (simulations) that show that direct drive has the potential to provide the high gains needed for a pure-fusion power plant. Two competing lasers are under development: the diode-pumped solid-state laser (DPPSL) and the electron-beam-pumped krypton fluoride (KrF) gas laser. This paper will present the current state of the art in the target designs and lasers, as well as the other IFE technologies required for energy, including final optics (grazing incidence and dielectrics), chambers, and target fabrication, injection, and tracking technologies. All of these are applicable to both laser systems and to other laser IFE-based concepts. However, in some of the higher performance target designs, the DPPSL will require more energy to reach the same yield as with the KrF laser.

Simulation of fabrication variations in supernova hydrodynamics experiments

Recent experiments at the Omega laser facility have used ∼4.5 kJ of energy to create a blast wave similar to the one that occurs in a core-collapse supernova. In the experiment, the blast wave crosses an interface with a drop in density similar to the He–H interface in a supernova, which induces the growth of a machined perturbation on the interface surface due to the Rayleigh–Taylor instability. These experiments have exhibited different morphology than our simulations predict. It has been hypothesized that such differences may be the result of unintended structures created in the target fabrication process. We have used 2D Cartesian simulations to model such fabrication variations using a branch of the hydrodynamic code FLASH. We have studied the convergence of these numerical models and developed analysis techniques to gauge and compare the impact each variation has on numerical results. In addition to this, we have implemented and verified a new viscosity package for our code. These accomplishments have allowed us to perform a thorough analysis of the effects that such fabrication variations have on our results through the use of numerical simulations.

Study of high-order harmonic generation from nanoparticles

An experimental study on high-order harmonic generation from the interaction of 45 fs Ti:sapphire laser pulses with preformed plasma plumes of metal nanoparticles was carried out. Highly efficient harmonic generation in the range of 9th order to 19th order was observed for Ag nanoparticles. The stability of harmonic generation was enhanced by utilizing special target fabrication techniques and through optimizing the conditions of plasma plume formation. Broadband harmonic generation was observed through the optimization of femtosecond laser intensity and through the use of spectrally broadened laser pulses. The harmonic generation was compared for various target materials (nano and bulk) and for Ag nanoparticle targets prepared from different fabrication techniques. Efficient generation of even- and odd-order harmonics was observed through the use of two-colour pulses. The observations can be explained qualitatively from symmetry breaking of high-order harmonic generation through the introduction of second harmonic pulses. The spectral broadening and shift of harmonic radiation can be understood from the self-modulation of the laser and harmonic radiation in the plasma.

Progress on LMJ targets for ignition

Targets designed to produce ignition on the Laser Megajoule (LMJ) are being simulated in order to set specifications for target fabrication. The LMJ experimental plans include the attempt of ignition and burn of an ICF capsule with 160 laser beams, delivering up to 1.4 MJ and 380 TW. New targets needing reduced laser energy with only a small decrease in robustness have then been designed for this purpose. Working specifically on the coupling efficiency parameter, i.e. the ratio of the energy absorbed by the capsule to the laser energy, has led to the design of a rugby-ball shaped cocktail hohlraum; with these improvements, a target based on the 240-beam A1040 capsule can be included in the 160-beam laser energy-power space. Robustness evaluations of these different targets shed light on critical points for ignition, which can trade off by tightening some specifications or by preliminary experimental and numerical tuning experiments.

Recent advances in development of materials for laser target

AbstractNearly ten years ago, a research program concerning materials and technologies was defined to develop the very complex cryogenic target for obtaining the combustion of a deuterium-tritium mixture by inertial confinement fusion in the laser megajoule facility. The CEA target fabrication project includes research and development on various organic polymers and materials for the cryogenic laser megajoule target assembly as well as for other targets that can be useful for the fusion program (pre and post-ignition). Recent advances have been accomplished concerning the development of specific organic materials for the fabrication of targets components, including the synthesis of polymers for the laser megajoule microshells and metal-doped organic foams for the elaboration of doped-foam microshells or for the micromachining of components.

Fabrication of aerogel capsule, bromine-doped capsule, and modified gold cone in modified target for the Fast Ignition Realization Experiment (FIREX) Project

The development of target fabrication for the Fast Ignition Realization EXperiment (FIREX) Project is described in this paper. For the first stage of the FIREX Project (FIREX-I), the previously designed target has been modified by using a bromine-doped ablator and coating the inner gold cone with a low-density material. A high-quality bromine-doped capsule without vacuoles was fabricated from bromine-doped deuterated polystyrene. The gold surface was coated with a low-density material by electrochemical plating. For the cryogenic fuel target, a brand new type of aerogel material, phloroglucinol/formaldehyde (PF), was investigated and encapsulated to meet the specifications of 500 µm diameter and 20 µm thickness, with 30 nm nanopores. Polystyrene-based low-density materials were investigated and the relationship between the crosslinker content and the nanopore structure was observed.