Inertial Fusion Science Research Articles

Extreme-UV absorption processes in a laser-produced mid-Z plasma: Measurements and theoretical interpretation

A good knowledge of absorption properties of plasmas at temperature of few tens of eV is essential in several domains such as astrophysics and inertial fusion science. For instance the description of stellar envelopes or the analysis of beta-Cephei pulsation requires an accurate determination of the Rosseland absorption coefficient, which strongly depends on the radiative properties of plasmas in the extreme-UV (XUV) range. Contrary to measurements in X-ray range, the literature on the absorption properties of plasmas of mid-Z elements in XUV domain is less abundant. Furthermore the theoretical interpretation of such spectra represents a theoretical challenge since this energy range involves transition arrays from n equal 3 to 3 with an approximately half-open 3d subshell and possibly other open spectator subshells which contain a huge number of lines. The aim of this paper is to describe an experiment recently performed on the LULI 2000 laser facility mostly devoted to measurements of the absorption in the 60 – 180 eV spectral region in a copper plasma at a temperature of 10 to 30 eV and a density of few mg/cm3. The experimental scheme is based on an indirect heating of multilayer thin foils by two gold cavities irradiated by two nanosecond doubled-frequency beams with an energy of several hundreds of J. This scheme allows one to obtain moderate temperature- and density-gradients and ensures conditions close to local thermodynamic equilibrium. The self-emission of cavities in XUV range is tentatively eliminated by the use of a time-dependent detection. A preliminary interpretation of these measurements is proposed. This analysis relies on three different codes: the hybrid code SCO-RCG, the Flexible Atomic Code in detailed or configuration-average mode, and the HULLAC code in level or configuration mode. A partial agreement is obtained between theory and experiment, though the account for temperature gradients is probably necessary to accurately describe the present measurements.

A journey through high-energy-density physics

The present paper is based upon the Teller Award lecture by the author, at the Inertial Fusion Sciences and Applications conference in September, 2017. It provides a very selective review of several topics in high-energy-density physics, discussing research in which the author participated and making connections to more recent and ongoing work. Topics discussed at some length include stimulated Raman scattering from laser beams containing much structure, plasma hydrodynamics and the applications it makes possible, and radiative shocks. Several other topics are discussed more briefly.

Opacity calculations in X and XUV range using a detailed atomic code

Calculations of accurate opacities in X and XUV range are of high interest for several domains such as astrophysics or inertial fusion science. Such quantities may be investigated through laser‐plasma interaction in the indirect‐drive scheme. In this work absorption properties of such plasmas are analysed using the Flexible Atomic Code. Detailed and unresolved‐transition‐array modes are investigated, and some results obtained with the mixed mode recently developed are also proposed. For a carbon plasma the present approach agrees with the results obtained with the superconfiguration code SCO. Some results are provided about the X‐ray opacity of nickel, and a comparison with data from a recent campaign on LULI 2000 facility is done. This comparison demonstrates that the Unresolved Transition Array approach may be insufficient, e.g., to determinate the accurate position and shape of the 2p–3d structure in nickel at about 25 eV. The case of non‐electric‐dipole‐type transitions, such as magnetic dipole transitions is addressed. The electric‐dipole and magnetic‐dipole transitions are studied here in the case of the 3 * n complex of five tungsten ions, with charge states similar to those found in the tokamak divertors. It is demonstrated that the unresolved transition array formulas provide a fairly accurate description of the most important absorption structures, but fail to reproduce correctly the behavior of the opacity in the wings of these main structures.

The equation of state package FEOS for high energy density matter

The equation of state package FEOS for high energy density matter

Preface

The Ninth International Conference on Inertial Fusion Science and Applications (IFSA) was held on September 20-25, 2015 at the Hyatt Regency Bellevue on Seattle’s Eastside, Washington, U.S.A. The event was hosted by the University of California and was organized by the Lawrence Livermore National Laboratory. It brought together more than 370 participants from 16 countries.The goal, as for all previous IFSA Conferences, was to bring together scientists in the fields of inertial fusion science and high-energy-density physics, and their applications. Three hundred twenty seven papers were presented emphasizing the science of high-energy and high-intensity laser, pulsed-power, and particle-beam interactions with matter, the associated high-energy-density physics, and their application to fusion concepts. Results presented included theory, modeling, and experimental results from facilities worldwide.In recent years, significant advances have been made in high-energy-density science using lasers, Z-pinches, and particle beam systems with dramatic technical achievements in areas such as central-hot-spot ignition, fast and impulse ignition, material properties at extreme conditions, warm dense matter, particle acceleration and laser-plasma interactions. For the first time in the laboratory, x-ray driven ignition experiments, performed at the National Ignition Facility (NIF) in the United States, have exhibited self-heating. In the month following the Conference, the first plasma experiments were performed at Laser Mégajoule (LMJ) in France, and ignition scale projects are under way in China and Russia. Other approaches, such as magnetic compression on the Z-machine at Sandia National Laboratories and direct drive experiments at the University of Rochester, have produced exciting new results which were reported on at the Conference.Second-generation petawatt short-pulse laser systems such as the highest-energy petawatt laser systems LFEX (FIREX) in Japan, OMEGA-EP in the United States, PETAL in France, and Vulcan PW in the United Kingdom, have allowed the study of novel approaches to producing and probing high-energy-density matter and exploring alternative ignition schemes. These scientific studies contribute to the physics understanding needed to develop inertial fusion energy as a commercial energy source and were also reported on at the Conference.Third-generation rep-rated and high-energy petawatt lasers are coming on line for strong field science studies and have opened up a new field of relativistic plasma physics. The extreme states achieved in these laser-plasma interactions are relevant to high-intensity x-ray applications, material processing, novel accelerators, and laboratory astrophysics.Recent activities and research in all these fields were discussed in 327 presentations, including three Keynote lectures, two Teller lectures, 21 plenary talks, 135 orals, and 166 posters. The proceedings collected in this volume underwent a rigorous peer-review process. The Editor is thankful to all the authors who agreed to act as referees on papers written by their fellow authors, and who worked both hard and diligently to complete this task in record time. We also thank the Technical Program Committee members who helped make this Ninth IFSA Conference possible.The American Nuclear Society Teller Award was bestowed during IFSA2015 on two key contributors to ICF science, Hiroshi Azechi and Jie Zhang. In addition, prizes were awarded to four students for their excellent presentations.On behalf of the various Committees, we extend our appreciation to everyone who helped make IFSA2015 a great success.

8th International Conference on Inertial Fusion Sciences and Applications (IFSA 2013)

PrefaceThe Eighth International Conference on Inertial Fusion Science and Applications was hosted on 8-13 September 2013 at the Nara Prefectural New Public Hall, organized by the Institute of Laser Engineering, Osaka University. It brought together 394 participants from 19 countries. The common goal was to share the latest advances in the fields of inertial fusion energy, laser and particle beams and fusion technology as well as high-energy density physics and applications. There were 393 presentations in total including three Keynote lectures, two Teller lectures, 17 plenary talks, 132 orals and 236 posters. Three IAEA-TM joint papers were presented during the Conference week. The proceedings collected in this volume underwent a rigorous peer-review process for which the Editors are thankful to the many referees who worked very hard to finalize the publication. They also thank the TPC members whose work made such a wonderful Conference program.Among the tremendous achievements presented, the great progress in experiments on NIF aimed at ICF ignition was one of the most important highlights. Significant progress in high-energy density science was another important topic in this IFSA2013.Of course many other excellent papers on various subjects were presented showing the continuous growth of the related fields.The Teller Award was bestowed during IFSA2013 on two key contributors to ICF science, J. Hammer and R. Petrasso. The student prize was awarded for six excellent papers presented by students from various countries.On behalf of the various Committees, we are glad to thank again everyone who helped make IFSA2013 a great success.Hiroshi AzechiHiroyuki Shiraga

Spectroscopic measurements of temperature and plasma impurity concentration during magnetic reconnection at the Swarthmore Spheromak Experiment

Electron temperature measurements during counterhelicity spheromak merging studies at the Swarthmore Spheromak Experiment (SSX) [M. R. Brown, Phys. Plasmas 6, 1717 (1999)] are presented. VUV monochromator measurements of impurity emission lines are compared with model spectra produced by the non-LTE excitation kinematics code PRISMSPECT [J. J. MacFarlane et al., in Proceedings of the Third Conference on Inertial Fusion Science and Applications (2004)] to yield the electron temperature in the plasma with 1 μs time resolution. Average Te is seen to increase from 12 to 19 eV during spheromak merging. Average C III ion temperature, measured with a new ion Doppler spectrometer (IDS) [C. D. Cothran et al., Rev. Sci. Instrum. 77, 063504 (2006)], likewise rises during spheromak merging, peaking at ∼22 eV, but a similar increase in Ti is seen during single spheromak discharges with no merging. The VUV emission line measurements are also used to constrain the concentrations of various impurities in the SSX plasma, which are dominated by carbon, but include some oxygen and nitrogen. A burst of soft x-ray emission is seen during reconnection with a new four-channel detector (SXR). There is evidence for spectral changes in the soft x-ray emission as reconnection progresses, although our single-temperature equilibrium spectral models are not able to provide adequate fits to all the SXR data.

One-megajoule, wetted-foam target-design performance for the National Ignition Facility

Wetted-foam, direct-drive target designs are a path to high-gain experiments on the National Ignition Facility (NIF) [J. Paisner et al., Laser Focus World 30, 75 (1994)]. Wetted-foam designs [S. Skupsky et al., in Inertial Fusion Sciences and Applications 2001, edited by K. Tanaka, D. D. Meyerhofer, and J. Meyer-ter-Vehn (Elsevier, Paris, 2002)] take advantage of the increased laser absorption provided by the higher-atomic-number elements in a target ablator composed of plastic foam saturated with deuterium-tritium (DT). The increased laser coupling allows more fuel to be driven with the same incident laser energy, resulting in increased hydrodynamic stability and target gain. A stability analysis of a 1-MJ design was performed using the two-dimensional hydrodynamic code DRACO [P. B. Radha et al., Phys. Plasmas 12, 032702 (2005)]. Simulations examining the effect of the expected levels of laser nonuniformities (single-beam and multiple-beam) and target nonuniformities (surface and ice roughness) have been performed. A nonuniformity-budget analysis has been constructed and suggests that two-dimensional (2D) smoothing by spectral dispersion (SSD) [S. Skupsky et al., J. Appl. Phys. 66, 3456 (1989)] is needed to reduce single-beam nonuniformities to levels sufficient for ignition to proceed. Two integrated 2D simulations with 0.75-μm initial ice roughness, multiple-beam nonuniformity, surface roughness, and imprint were completed, one with 2D SSD smoothing and one with 1D SSD. The former ignited and produced a gain of 32, while the latter failed to ignite. A third integrated 2D simulation with 1-μm initial ice roughness and an ice power-law spectral index of 1 was also completed and produced a gain of 27.

X-ray imaging with grazing-incidence microscopes developed for the LIL program

This article describes x-ray imaging with grazing-incidence microscopes, developed for the experimental program carried out on the Ligne d'Integration Laser (LIL) facility [J. P. Le Breton et al., Inertial Fusion Sciences and Applications 2001 (Elsevier, Paris, 2002), pp. 856-862] (24 kJ, UV-0.35 nm). The design includes a large target-to-microscope (400-700 mm) distance required by the x-ray ablation issues anticipated on the Laser MégaJoule facility [P. A. Holstein et al., Laser Part. Beams 17, 403 (1999)] (1.8 MJ) which is under construction. Two eight-image Kirkpatrick-Baez microscopes [P. Kirkpatrick and A. V. Baez J. Opt. Soc. Am. 38, 766 (1948)] with different spectral wavelength ranges and with a 400 mm source-to-mirror distance image the target on a custom-built framing camera (time resolution of approximately 80 ps). The soft x-ray version microscope is sensitive below 1 keV and its spatial resolution is better than 30 microm over a 2-mm-diam region. The hard x-ray version microscope has a 10 microm resolution over an 800-microm-diam region and is sensitive in the 1-5 keV energy range. Two other x-ray microscopes based on an association of toroidal/spherical surfaces (T/S microscopes) produce an image on a streak camera with a spatial resolution better than 30 microm over a 3 mm field of view in the direction of the camera slit. Both microscopes have been designed to have, respectively, a maximum sensitivity in the 0.1-1 and 1-5 keV energy range. We present the original design of these four microscopes and their test on a dc x-ray tube in the laboratory. The diagnostics were successfully used on LIL first experiments early in 2005. Results of soft x-ray imaging of a radiative jet during conical shaped laser interaction are shown.

Inertial fusion science in Europe

Europe has built significant laser facilities to study ICF since the beginning of this science. The goal is to understand the processes of ignition and propagation of thermonuclear combustion. Three routes toward fusion are pursued, each of which has advantages and difficulties. The conventional routes are using a central hot spot created by the same compression and heating laser beams, either with indirect or direct drive. A more recent route, fast ignition, has been actively studied since the 90's, increasing the need for PW high energy lasers to create the hot spot; some European lasers of this kind are already functioning, others are under construction or planned. Among European facilities, Laser Mega Joule (LMJ), which is under construction, will be the most powerful tool at the end of the decade, along with NIF in the USA, to study and obtain fusion. On all these facilities, numerous results are and will be obtained in the fields of High Energy Density Physics (HEDP) and Ultra High Intensity (UHI).

Overview of inertial fusion and high-intensity laser plasma research in Europe

Inertial fusion science is driven by ‘the quest for ignition’. For many years, a ‘conventional’ route towards inertial fusion has been investigated using two different approaches: ignition by an inertial central hot spot could be obtained either through the direct or the indirect drive scheme. Both imply the use of a very large facility to operate the driver, which is a powerful laser in the current projects (LMJ in France as well as NIF in the US). The LMJ construction being on the way, a large amount of experimental and computational work is currently being done to deepen the understanding of ignition requirements.On the other hand, the so-called ‘fast ignition’ approach has led to an increasingly important amount of scientific work since it was proposed at the beginning of the 1990s. During the last several years (from the previous IFSA held in Kyoto in 2001), several PW-class high-intensity laser facilities have been built in Europe.In the meantime, a large number of interesting results related to fast electron and proton production have been obtained with the existing facilities. Observation of laser-irradiated solid targets has provided the first evidence of electron bunches separated by half the period of light. Nevertheless, target heating remains modest. On the other hand, multi-megaelectronvolt highly collimated electron beams have been produced by table-top lasers interacting with the low-density plasmas. They open the feasibility of a lot of applications: x-ray probe beams in plasma physics, biology, chemistry, injector for conventional accelerators, etc). Laser-produced proton beams is also a growing field, with a lot of promising applications: proton therapy, radio-isotope production, diagnostic for transient phenomena in laser–plasma interaction, etc.Inertial fusion research is fostered by a sustained effort of organization and coordination at the national level (the creation of an Institute for Lasers and Plasmas in France) as well as at the European level (within the 6th Framework Program).

Landau–Darrieus instability in an ablation front

An analytical model that shows the conditions for the existence of the Landau–Darrieus instability of an ablation front is presented. The model seems to agree with recently claimed simulation results [L. Masse et al., Proceedings of the 1st International Conference on Inertial Fusion Sciences and Applications (Elsevier, Paris, 2000), p. 220]. The model shows that the ablation front can be unstable in absence of gravity when the thermal flux is inhibited within the supercritical region of the corona.

Inertial fusion science and technology for the 21 [formula omitted] century

This paper reviews the leading edge of the basic and applied science that use high-intensity facilities. The more than 15 000 experiments on the Nova laser since 1985 and many thousands more on other laser, particle beam, and pulsed power facilities around the world have established the new laboratory field of high-energy-density plasma physics and have furthered development of inertial fusion. High-brightness femtosecond lasers have enabled the study of matter in conditions previously unachievable on earth. These experiments and advanced calculations have established the specifications for the National Ignition Facility (NIF) and Laser MegaJoule (LMJ) and have enhanced scientific fields such as laboratory astrophysics. Science and technology developed in inertial fusion have found near-term commercial use, have enabled steady progress toward the goal of fusion ignition and gain in the laboratory, and have opened up new fields of study for the 21 st century.

The National Ignition Facility - applications for inertial fusion energy and high-energy-density science

Research in inertial fusion sciences and applications worldwide is making dramatic progress. The National Ignition Facility (NIF) in the US and the Laser MegaJoule (LMJ) in France are being built to achieve fusion ignition in the laboratory. Experiments that have been done on current Inertial Confinement Fusion (ICF) facilities in the US and around the world have demonstrated that the drive characteristics required for ignition are now well understood and a new plan for inertial fusion energy development has been put together by the community. Besides examining the conditions necessary for fusion ignition, targets were designed without fusion capsules. Equilibrium temperatures of hundreds of electron volts and megabar pressures were used to study astrophysical processes and measure equations of states at these extreme conditions. Recent studies of laser-matter interactions with femtosecond lasers have revealed some startling new phenomena due to the ability to achieve irradiances >1020 W cm-2. This paper will review recent results in fusion and high energy density science achieved by high intensity lasers at LLNL and will look ahead to what may achieved on NIF.