Table of contents

The Third International Conference on Inertial Fusion Sciences and Applications (IFSA2003) was held in Monterey, CA, USA, on 7--12 September 2003. The goal of IFSA2003 was to bring together scientists and engineers in the fields of inertial fusion sciences, high energy density physics, inertial fusion energy (IFE) and other related research and applications. By all measures IFSA2003 was a resounding success.

IFSA2003 was hosted by the University of California, which was supported in organizing the conference by seven institutions: General Atomics, Lawrence Berkeley National Laboratory, Lawrence Livermore National Laboratory, Los Alamos National Laboratory, Naval Research Laboratory, Sandia National Laboratory and the University of Rochester, Laboratory for Laser Energetics.

IFSA2003 was the largest IFSA conference yet with 405 participants from 17 countries. Approximately 430 papers were presented and 236 appeared in the Proceedings, published in July 2004 by the American Nuclear Society [1]. A subset of the Nuclear Fusion Board of Editors, those who work on inertial confinement fusion (ICF), recommended creating this special issue of Nuclear Fusion by selecting a representative cross-section of the papers presented at IFSA2003. Authors of the selected papers were asked to expand their papers and make them suitable for publication in it Nuclear Fusion.

Nineteen papers are presented in this special issue. They represent a cross-section of the papers presented at IFSA2003. However, there was no attempt to represent the `feel' of the conference by having the same fraction of papers on each topic as existed at IFSA. There were far more detailed scientific papers at IFSA than are presented in this special issue. However, in the interest of giving the reader a cross-section of the papers and showing the entire breadth of ICF research going on, we have biased the selection process toward review papers.

The first three papers here are based upon the keynote talks at IFSA2003 and are, therefore, overviews of all ICF research being done in the Americas, Asia, and Europe. The next two papers are also reviews but of a different sort. The Teller Medal is awarded at the IFSA conferences for pioneering work and leadership in inertial fusion and high energy density science. The two recipients for 2003 were H. Takabe of the Institute of Laser Engineering at Osaka University and L. Suter of Lawrence Livermore National Laboratory. These awardees were asked to deliver the two Teller Lectures at IFSA based upon the work for which they were being honoured. The papers presented here are expansions of those two review talks. Suter chose to focus his review on his recent work on ignition physics for targets driven by 0.54 m light. This is of interest because large facilities like the National Ignition Facility (NIF) will deliver much more energy in the frequency doubled wavelength than in the frequency tripled one. Takabe, on the other hand chose to give a historical perspective of his lifelong work.

The other 14 papers were selected to represent a cross-section of the research being conducted in the science and engineering of inertial fusion. The papers by Haan et al and Holstein et al represent some of the recent progress in target design calculations for the ignition first experiments. Haan presents his team's work on indirect drive ignition targets (driven by 0.35 m) intended for the National Ignition Facility (NIF) when all the beamlines are activated. Holstein does the same for targets being design for the Laser MegaJoule (LMJ). Suter's paper, presented earlier as a Teller Lecture also falls into this ignition target physics category.

The next four papers look at some of the exciting high energy density physics being studied in ICF facilities around the world. Glenzer et al looks at stimulated light scattering processes in hot dense plasmas. Pukhov et al look at relativistic laser-plasma interactions that produce energetic particles and x-rays. Peyrusse et al examine atomic physics and radiative processes in hot dense plasmas. Koenig et al examine ways to simulate planetary physics processes using high pressures generated in laser driven shocks.

Non-laser approaches to inertial fusion were also fully represented at IFSA2003. The paper by Lebedev et al shows important physics developments in Z-pinch plasmas. Sharp et al present chamber transport modelling for heavy ion fusion drivers.

Technology development studies were also well represented at IFSA2003. There was a special session on facility and driver developments that contained several papers. Presented here are the papers by Miller et al on the NIF, Danson et al on the Vulcan petawatt facility, and Myers et al on KrF lasers for IFE. A paper by Goodin et al shows progress in finding cost effective target manufacturing methods for IFE.

Finally, there were many papers at IFSA2003 that focused upon the very promising but more immature field of fast ignition. Barty et al give an overview of the development issues for short pulse lasers that will be essential if fast ignition is to become mainstream. A paper by Kodama et al looks at target physics using cone focus targets. Fast ignition lasers and innovative target physics within this concept were a `hot topic' at IFSA2003.

The IFSA conferences have become the principal forum for the exchange of research results in inertial fusion and high energy and density science. There is a unique blend of science and technology. All fields of inertial fusion are represented. This special issue is a snapshot and a cross-section of the field at this time. We hope the reader is encouraged to look into more of the papers in areas that interest them.

References

[1] Inertial Fusion Sciences and Applications: State of the Art 2003 ed B. Hammel, D. Meyerhofer, J. Meyer-ter-Vehn and H. Azechi American Nuclear Society (July 2004) These IFSA2003 proceedings may be purchased on-line at http://www.ans.org.

Significant progress has been made in the United States Inertial Confinement Fusion (ICF) Program since the IFSA conferences in Bordeaux (1999) and Kyoto (2001). This progress has covered all areas of ICF from target design to implosion experiments. It is capped by experimental results from cryogenic direct-drive targets on OMEGA and new results from the first quad of the National Ignition Facility (NIF). This paper will briefly highlight some of the new results that give increasing confidence in the achievement of ignition in the NIF.

The present status and future prospects of IFE research and high power laser applications in Asia are reviewed. At ILE, Osaka University, the Gekko XII and the Peta Watt laser system have been operated to investigate implosion hydrodynamics, fast ignition and relativistic laser plasma interactions. In particular, fast ignition experiments with cone shell targets have been carried out as joint UK–Japan and US–Japan collaboration programmes. In the experiments, imploded high density plasmas are heated by a 500 J level petawatt laser pulse. The thermal neutron yield is found to increase by three orders of magnitude by petawatt laser injection to the cone shell target.

Laser plasma physics related to laser fusion and other applications has been studied at many institutes in Asia. Areas of research include Rayleigh–Taylor instability experiments, application of extreme ultraviolet radiation sources for lithography, laser particle acceleration, and x-ray lasers, to name a few.

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).

For several years we have been exploring the possibility of using green (2ω) light for indirect drive ignition on National Ignition Facility (NIF). This paper is a comprehensive review of our progress in this investigation and was the subject of a Teller lecture when one of the authors (LJS) was honoured with the Edward Teller Medal at the IFSA03 conference on September 12th, 2003, at Monterey, CA. While much of the work presented here has been previously published (Suter L.J. et al 2004 Phys. Plasmas11 2738) and is included for completeness of the review, this paper also includes new research examining the possibility of higher temperature (300 eV) ignition hohlraums driven by green light (section 7).

The author reviews fusion science and its extension to astrophysics in the field of theory and computation by picking up five topics. The first is the ablative stabilization of a Rayleigh–Taylor instability at an ablation front and its dispersion relation, the so-called Takabe formula. This formula gives a principal guideline for stable target design and is also applied to studying the turbulent combustion wave in Type Ia supernova explosions. The second is the development of the integrated code ILESTA. The physics of an integrated code, ILESTA (one- and two-dimensional), and analyses and design of laser produced plasmas including the implosion dynamics and stability are reviewed. There are two areas on its applications to implosion analysis: one is an evaluation of mixing layers in one-dimensional implosions by coupling with one- and two-dimensional ILESTA and the other is an extension to include the k–ε type turbulent mixing model, where the details of the formulation are given. The third topic is laboratory astrophysics with intense lasers. This consists of two parts: one is a review of its historical background and the other is on how we relate laser plasmas to wide-ranging astrophysics and the purposes of promoting such research. The fourth topic is on anomalous transport of relativistic electrons in fast ignition laser fusion and its relation to self-organization of magnetic field generation in gamma-ray bursts at cosmological distances. Finally, recent activity related to the application of the author's experience to the development of an integrated code for studying extreme phenomena in astrophysics is briefly explained.

Studies on simulation and design of ignition targets for the National Ignition Facility (NIF) are described. Recent effort has emphasized the systematic exploration of the parameter space of possible ignition targets, providing comparisons as specific as possible between the various targets. This study aims at providing guidance for target fabrication R&D, and for other elements of the ignition program. Targets are being considered that span 250–350 eV drive temperatures, capsule energies from 150 to 600 kJ, cocktail and gold hohlraum spectra, and three ablator materials (Be[Cu], CH[Ge] and polyimide). Capsules with graded doped beryllium ablators are found to be very stable with respect to short-wavelength Rayleigh–Taylor growth. Sensitivity to ablator roughness, ice roughness and asymmetry is being explored, as it depends on ablator material, drive temperature and absorbed energy. Three-dimensional simulations are being used to ensure adequate radiation symmetry in three dimensions (3D), and to ensure that coupling of 3D asymmetry and 3D Rayleigh–Taylor does not adversely affect planned performance. Integrated 3D hohlraum simulations indicate that 3D features in the laser illumination pattern affect the hohlraums' performance, and the hohlraum has been redesigned to accommodate these effects.

First we report two studies aimed at preparing laser integration line (LIL) experiments (LIL is the prototype of LMJ): deflection of a beam with and without 'longitudinal' smoothing (associated with focusing by gratings) and the radiation temperature, T_r, in a hohlraum with long pulses (10–20 ns). Experimentally, we did not see any Langmuir decay instability able to saturate the stimulated Raman scattering in a gas bag irradiated with the Omega laser. Next, in our hydro-code FCI2, we implemented an improved version of the non-LTE atomic physics model: the change in T_r in the hohlraum is negligible, but now the simulations are in agreement with experiments on x-ray conversion and on Rayleigh–Taylor instabilities (RTIs) in a spherical geometry. The RTIs in polyimide foil at 70 µm were understood, but not those at 30 µm. Finally, for the target design, we confirm the hydro-stability of the four targets of the operational domain of LMJ: the doped CH ablator of the nominal target can withstand a roughness in the range 50–100 nm. The robustness studies use 19 uncertainties coming from the laser power, the beam pointing and the target fabrication. Finally, the burning of DT has been studied in detail, identifying three regimes.

The first experiments on the National Ignition Facility (NIF) have employed the first four beams to measure propagation and laser backscattering losses in large ignition-size plasmas. Gas-filled targets between 2 and 7 mm length have been heated from one side by overlapping the focal spots of the four beams from one quad operated at 351 nm (3ω) with a total intensity of 2 × 10¹⁵ W cm⁻². The targets were filled with 1 atm of CO₂ producing up to 7 mm long homogeneously heated plasmas with densities of n_e = 6 × 10²⁰ cm⁻³ and temperatures of T_e = 2 keV. The high energy in an NIF quad of beams of 16 kJ, illuminating the target from one direction, creates unique conditions for the study of laser–plasma interactions at scale lengths not previously accessible. The propagation through the large-scale plasma was measured with a gated x-ray imager that was filtered for 3.5 keV x-rays. These data indicate that the beams interact with the full length of this ignition-scale plasma during the last ∼1 ns of the experiment. During that time, the full aperture measurements of the stimulated Brillouin scattering and stimulated Raman scattering show scattering into the four focusing lenses of 3% for the smallest length (∼2 mm), increasing to 10–12% for ∼7 mm. These results demonstrate the NIF experimental capabilities and further provide a benchmark for three-dimensional modelling of the laser–plasma interactions at ignition-size scale lengths.

Using direct three-dimensional particle-in-cell (PIC) simulations we study the acceleration of electrons and ions in laser–plasma. The PIC simulations allow us to understand the results of actual experiments better, and to look beyond the presently available technology and model for laser parameters that will be obtained in the nearest future. The code VLPL (Virtual Laser-Plasma Laboratory) has been further developed and now it can model the x-ray emission by relativistic electrons in the synchrotron regime. It appears that the strongly non-linear plasma wave excited by a short laser pulse works as a compact high-brightness source of x-ray radiation. We have also checked the possibility of proton trapping in the non-linear plasma wave and find that this is already possible at intensities around 10²² W cm⁻².

The understanding of ICF plasmas requires specific quantities such as average ionizations, emissivities and opacities, both for hydro-simulations and diagnostics. These quantities clearly involve the internal state of the ions. The well-known traditional few-electron atomic physics provides such satisfactory quantities for LTE and NLTE plasmas. On the other hand, calculations for high-Z plasmas containing open-shell complex ionic emitters have been attempted only recently. Because of the very large density of states in such ions, these calculations are based upon statistical considerations about the energy levels and the collisional-radiative rates rather than individual level or process accounting. Complex many-electron excited levels may have purely statistical, i.e. thermally induced, properties or intrinsic statistical properties due to the mixing of a large number of electron configurations. We review these statistical properties and we sum up the advances in complex atom physics which improve our capabilities to model radiative properties of hot dense plasmas.

High power lasers are a tool that can be used to determine important parameters in the context of Warm Dense Matter, i.e. at the convergence of low-temperature plasma physics and finite-temperature condensed matter physics. Recent results concerning planet inner core materials such as water and iron are presented. We determined the equation of state, temperature and index of refraction of water for pressures up to 7 Mbar. The release state of iron in a LiF window allowed us to investigate the melting temperature near the inner core boundary conditions. Finally, the first application of proton radiography to the study of shocked material is also discussed.

We report on experiments on the MAGPIE generator (1 MA, 250 ns) to study the physics of plasma formation in wire array Z-pinches. It is shown that the gradual redistribution of the array mass by the precursor plasma flow from wire cores plays a very important role in implosion dynamics. It is found that the rate of wire ablation depends on the magnitude of the global (collective) magnetic field of the array and increases with the field. Due to this dependence, the azimuthal variations of the global magnetic field affect the implosion dynamics. The existence of the modulation of the ablation rate along the wires leads to the presence of a 'trailing' mass left behind by the imploding current sheath. The trailing mass provides an alternative path for the current, reducing the force available for compression of the pinch at stagnation. The observed dependence of the ablation rate on inter-wire separation suggests an explanation for the existence of the optimal wire number maximizing the x-ray power.

The heavy-ion fusion community recently developed a power-plant design that meets the various requirements of accelerators, final focus, chamber transport and targets. The point design is intended to minimize physics risk and is certainly not optimal for the cost of electricity. Recent chamber-transport simulations, however, indicate that changes in the beam ion species, the convergence angle and the emittance might allow more-economical designs.

The National Ignition Facility (NIF) at Lawrence Livermore National Laboratory, when completed in 2008, will contain a 192-beam, 1.8 MJ, 500 TW, ultraviolet laser system together with a 10 m diameter target chamber and room for 100 diagnostics. NIF is housed in a 26 000 m² environmentally controlled building and is the world's largest and most energetic laser experimental system. NIF provides a scientific centre for the study of inertial confinement fusion and the physics of matter at extreme energy densities and pressures. NIF's energetic laser beams will compress fusion targets to conditions required for thermonuclear burn, liberating more energy than required to initiate the fusion reactions. Other NIF experiments will study physical processes at temperatures and pressures approaching 10⁸ K and 10¹¹ bar, respectively, conditions that exist naturally only in the interior of stars and planets. NIF is currently configured with four laser beams activated in late 2002. These beams are being regularly used for laser performance and physics experiments, and to date nearly 250 system shots have been conducted. NIF's laser beams have generated 106 kJ in 23 ns pulses of infrared light and over 16 kJ in 3.5 ns pulses at the third harmonic (351 nm). A number of target experimental systems are being commissioned in support of experimental campaigns. This paper provides a detailed look at the NIF laser systems, laser and optical performance, and results from laser commissioning shots. We also discuss NIF's high-energy density and inertial fusion experimental capabilities, the first experiments on NIF, and plans for future capabilities of this unique facility.

The Vulcan Nd : glass laser at the Central Laser Facility is a Petawatt (10¹⁵ W) interaction facility available to the UK and international user community. The facility came online to users in 2002 and considerable experience has been gained operating the Vulcan facility in this mode. The facility is designed to deliver irradiance on target of 10²¹ W cm⁻² for a wide-ranging experimental programme in fundamental physics and advanced applications. This includes the interaction of super-high-intensity light with matter, fast ignition fusion research, photon induced nuclear reactions, electron and ion acceleration by light waves and the exploration of the exotic world of plasma physics dominated by relativity.

Krypton fluoride (KrF) lasers produce highly uniform beams at 248 nm, allow the capability of 'zooming' the spot size to follow an imploding pellet, naturally assume a modular architecture and have been developed into a pulsed-power-based industrial technology that readily scales to a fusion power plant sized system. There are two main challenges for the fusion power plant application: to develop a system with an overall efficiency of greater than 6% (based on target gains of 100) and to achieve a durability of greater than 3 × 10⁸ shots (two years at 5 Hz). These two issues are being addressed with the Electra (700 J, 5 Hz) and Nike (3000 J, single shot) KrF lasers at the Naval Research Laboratory. Based on recent advances in pulsed power, electron beam generation and transport, hibachi (foil support structure) design and KrF physics, wall plug efficiencies of greater than 7% should be achievable. Moreover, recent experiments show that it may be possible to realize long lived electron beam diodes using ceramic honeycomb cathodes and anode foils that are convectively cooled by periodically deflecting the laser gas. This paper is a summary of the progress in the development of the critical KrF technologies for laser fusion energy.

A central feature of an inertial fusion energy (IFE) power plant is a target that has been compressed and heated to fusion conditions by the energy input of the driver. This is true whether the driver is a laser system, heavy ion beams or Z-pinch system. The IFE target fabrication, injection and tracking programmes are focusing on methods that will scale to mass production. We are working closely with target designers, and power plant systems specialists, to make specifications and material selections that will satisfy a wide range of required and desirable target characteristics. One-of-a-kind capsules produced for today's inertial confinement fusion experiments are estimated to cost about US$2500 each. Design studies of cost-effective power production from laser and heavy-ion driven IFE have suggested a cost goal of about $0.25–0.30 for each injected target (corresponding to ∼10% of the 'electricity value' in a target). While a four orders of magnitude cost reduction may seem at first to be nearly impossible, there are many factors that suggest this is achievable. This paper summarizes the design, specifications, requirements and proposed manufacturing processes for the future for laser fusion, heavy ion fusion and Z-pinch driven targets. These target manufacturing processes have been developed—and are proposed—based on the unique materials science and technology programmes that are ongoing for each of the target concepts. We describe the paradigm shifts in target manufacturing methodologies that will be needed to achieve orders of magnitude reductions in target costs, and summarize the results of 'nth-of-a-kind' plant layouts and cost estimates for future IFE power plant fuelling. These engineering studies estimate the cost of the target supply in a fusion economy, and show that costs are within the range of commercial feasibility for electricity production.

The technical challenges and motivations for high-energy, short-pulse generation with the National Ignition Facility (NIF) and possibly other large-scale Nd : glass lasers are reviewed. High-energy short-pulse generation (multi-kilojoule, picosecond pulses) will be possible via the adaptation of chirped pulse amplification laser techniques on NIF. Development of metre-scale, high-efficiency, high-damage-threshold final optics is a key technical challenge. In addition, deployment of high energy petawatt (HEPW) pulses on NIF is constrained by existing laser infrastructure and requires new, compact compressor designs and short-pulse, fibre-based, seed-laser systems. The key motivations for HEPW pulses on NIF is briefly outlined and includes high-energy, x-ray radiography, proton beam radiography, proton isochoric heating and tests of the fast ignitor concept for inertial confinement fusion.

We have developed a PW (0.5 ps/500 J) laser system to demonstrate fast heating of imploded core plasmas using a hollow cone shell target. Significant enhancement of thermal neutron yield has been realized with PW-laser heating, confirming that the high heating efficiency is maintained as the short-pulse laser power is substantially increased to a value nearly equivalent to the ignition condition. It appears that the efficient heating is realized by the guiding of the PW laser pulse energy within the hollow cone and by self-organized relativistic electron transport. Based on the experimental results, we are developing a 10 kJ-PW laser system to study the fast heating physics of high-density plasmas at an ignition-equivalent temperature.

The PDF file provided contains web links to all articles in this volume.