National Ignition Facility Laser System Research Articles

Performance measurements on NIF beamlines for future experiments to support polar direct drive

We are studying the implementation of polar direct drive (PDD) ignition experiments on the National Ignition Facility (NIF) laser system. Part of this preparation involves testing the performance of the NIF laser system over a broader span of center wavelengths, 3.6 nm, where the laser currently operates and that gain models describe. The temporal shape for the PDD pulses consists of a drive pulse preceded by three lower power “picket pulses”. These picket pulses require a multi-FM sinusoidal phase modulation format with a bandwidth of ∼ 200 GHz and a more dispersive grating in the preamplifier module (PAM) for smoothing-by-spectral-dispersion (SSD). In this paper we discuss recent measurements of gain on the NIF laser system over this broader wavelength range. We measured FM-to-AM conversion over the 3.6 nm wavelength range. The possibility of pinhole closure due to the larger bandwidth and dispersion associated with multi-FM SSD was studied at LLE on the OMEGA EP laser.

National Ignition Facility Laser System Performance

The National Ignition Facility (NIF) laser is the culmination of more than 40 years of work at Lawrence Livermore National Laboratory dedicated to the delivery of laser systems capable of driving experiments for the study of high-energy-density physics. Although NIF was designed to support a number of missions, it was clear from the beginning that its biggest challenge was to meet the requirements for pursuit of inertial confinement fusion. Meeting the Project Completion Criteria for NIF in 2009 and for the National Ignition Campaign (NIC) in 2012 included meeting the NIF Functional Requirements and Primary Criteria that were established for the project in 1994. During NIC and as NIF transitioned to a user facility, its goals were expanded to include requirements defined by the broader user community as well as by laser system designers and operators.

Direct-drive–ignition designs with mid-Z ablators

Achieving thermonuclear ignition using direct laser illumination relies on the capability to accelerate spherical shells to high implosion velocities while maintaining shell integrity. Ablator materials of moderate atomic number Z reduce the detrimental effects of laser–plasma instabilities in direct-drive implosions. To validate the physics of moderate-Z ablator materials for ignition target designs on the National Ignition Facility (NIF), hydro-equivalent targets are designed using pure plastic (CH), high-density carbon, and glass (SiO2) ablators. The hydrodynamic stability of these targets is investigated through two-dimensional (2D) single-mode and multimode simulations. The overall stability of these targets to laser-imprint perturbations and low-mode asymmetries makes it possible to design high-gain targets. Designs using polar-drive illumination are developed within the NIF laser system specifications. Mid-Z ablator targets are an attractive candidate for direct-drive ignition since they present better overall performance than plastic ablator targets through reduced laser–plasma instabilities and a similar hydrodynamic stability.

An initial assessment of three-dimensional polar direct drive capsule asymmetries for implosions at the National Ignition Facility

The National Ignition Facility (NIF) provides a unique opportunity to study implosion physics with nuclear yield. The use of polar direct drive (PDD) [A. M. Cok, R. S. Craxton, and P. W. McKenty, Phys. Plasmas 15, 082705 (2008)] provides a simple platform for the experimental studies without expensive optics upgrades to NIF. To determine the optimum PDD laser pointing geometry on NIF and provide a baseline for validating inertial confinement fusion codes against experiments for symmetric and asymmetric implosions, computer simulations using the 3D radiation-hydrodynamics code hydra [M. M. Marinak, R. E. Tipton, O. L. Landen, T. J. Murphy, P. Amendt, S. W. Haan, S. P. Hatchett, C. J. Keane, R. McEachern, and R. Wallace, Phys. Plasmas 3, 2070 (1996)] were preformed. The upper hemisphere of a DT-filled CH capsule was imploded by 96 NIF beams in a PDD configuration. Asymmetries in both polar and equatorial directions around the capsule were observed, with the former dominating the latter. Analysis of the simulation results indicates that the lack of symmetry in the initial power density profile (during the first 200 ps of the implosion) is a primary cause of late-time asymmetry in the implosion as well as decreased yield. By adjusting the laser pointings, the symmetry and total neutron yield were improved. Simulations with dropped quads (four of the NIF laser system’s 192 beamlines) without repointing worsen the overall symmetry by a factor of 10 (with respect to rms radial variation around the capsule) and reduce neutron yield by a factor of 2. Both of these degraded implosion characteristics are restored by azimuthal repointing of the remaining quads.

Demonstration of high-energy 2ω (5265 nm) operation on the National Ignition Facility Laser System

A single beamline of the National Ignition Facility (NIF) has been operated at a wavelength of 526.5 nm (2 omega) by frequency converting the fundamental 1053 nm (1 omega) wavelength with an 18.2 mm thick type-I potassium dihydrogen phosphate (KDP) second-harmonic generator (SHG) crystal. Second-harmonic energies of up to 17.9 kJ were measured at the final optics focal plane with a conversion efficiency of 82%. For a similarly configured 192-beam NIF, this scales to a total 2 omega energy of 3.4 MJ full NIF equivalent (FNE).

Fourier transform-based continuous phase-plate design technique: a high-pass phase-plate design as an application for OMEGA and the National Ignition Facility

A technique capable of calculating near-field, continuous phase diffractive optics (or phase plates) without phase dislocations and with optional far-field, speckle-spectrum control is introduced. The design technique improves upon a standard phase-retrieval method by adding convergence enhancements, phase continuity control, and far-field, speckle-spectrum control. The convergence enhancements improve the algorithm's efficiency. Phase continuity control eliminates phase dislocations and mitigates damaging retroreflections and transmissions. Specifying an optional constraint controls the far-field speckle spectrum. Application of these phase plates on the OMEGA and National Ignition Facility laser systems would produce well-controlled far-field spot shapes. High-pass phase-plate designs are compared with designs where the far-field spectrum is not controlled.

The National Ignition Facility

The National Ignition Facility (NIF) at Lawrence Livermore National Laboratory is a stadium-sized facility that, when completed in 2008, will contain a 192-beam, 1.8-megajoule, 500-terawatt, ultraviolet laser system together with a 10-m-diam target chamber and room for 100 diagnostics. NIF is the world's largest and most energetic laser ex- perimental system and will provide a scientific center to study inertial confinement fusion and matter at extreme energy densities and pres- sures. NIF's energetic laser beams will compress fusion targets to con- ditions required for thermonuclear burn, liberating more energy than re- quired to initiate the fusion reactions. Other NIF experiments will study physical processes at temperatures approaching 10 8 K and 10 11 bar, conditions that exist naturally only in the interior of stars and planets. NIF has completed the first phases of its laser commissioning program. The first four beams of NIF 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). NIF's target experimental systems are being commissioned and experi- ments have begun. This work provides a detailed look at the NIF laser systems, laser and optical performance, and results from recent laser commissioning shots. We follow this with a discussion of NIF's high- energy-density and inertial fusion experimental capabilities, the first ex- periments on NIF, and plans for future capabilities of this unique facility. © 2004 Society of Photo-Optical Instrumentation Engineers. (DOI: 10.1117/1.1814767) Subject terms: high-energy-density physics; inertial confinement fusion; labora- tory astrophysics; solid-state lasers.

The National Ignition Facility: enabling fusion ignition for the 21st century

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 national ignition facility high-energy ultraviolet laser system

The National Ignition Facility (NIF), currently under construction at the Lawrence Livermore National Laboratory, is a stadium-sized facility containing a 192-beam, 1 .&Megajoule, 500-Terawatt, ultraviolet laser system together with a 10-meter diameter target chamber with room for nearly 100 experimental diagnostics. When completed, NIF will be the world's largest and most energetic laser experimental system, providing an international center to study inertial confinement fusion and the physics of matter at extreme energy densities and pressures. NIF's 192 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 allow the study of physical processes at temperatures approaching 10{sup 8} K and 10{sup 11} Bar, conditions that exist naturally only in the interior of stars, planets and in nuclear weapons. NIF is now entering the first phases of its laser commissioning program. The first four beams of the NIF laser system have generated 106 kilojoules of infrared light and over 10 kJ at the third harmonic (351 nm). NIF's target experimental systems are also being installed in preparation for experiments to begin in late 2003. This paper provides a detailed look the NIF laser systems,more » the significant laser and optical systems breakthroughs that were developed, the results of recent laser commissioning shots, and plans for commissioning diagnostics for experiments on NIF.« less

VISRAD—A 3-D view factor code and design tool for high-energy density physics experiments

The 3-D view factor code VISRAD is used to both design high-energy density physics experiments, and to simulate the multi-dimensional radiation environment within target systems, i.e., hohlraums and associated components such as diagnostic holes, capsules, and backlighters. VISRAD target systems are built using a variety of geometric primitives, and surface removal algorithms (e.g., drilling holes in cylinders) can be employed to build complex targets. Laser beam parameters—power profiles, pointing, and focusing—can be specified for either individual beams or groups of beams. At present, the OMEGA and National Ignition Facility laser systems are supported by VISRAD. The use of multiple coordinate systems is supported so that target components can be positioned and oriented, and laser beams can be pointed, in the target chamber coordinate system or in the coordinate system of any target component. Radiation flux distributions about the target system are computed by solving a coupled set of power balance equations in which the emission from a given surface element in the target grid is coupled to all other surface elements. Accurate algorithms are used in computing the configuration (view factor) integrals. At any point in the grid, the time- and frequency-dependent flux incident onto that point can be viewed and/or written to a file to be used as input to radiation-hydrodynamics simulations. Energy source models include laser energy deposition—computed using 3-D ray-trace algorithms—and self-radiating target components. To aid designers in setting up targets, pointing beams, and viewing results, VISRAD has an easy-to-use graphical user interface and interactive 3-D graphics. The code has been designed for cross-platform use on Windows, Unix, and Mac OS X platforms.