Biggest Laser

Appl Opt.  2011 Mar 10;50(8):1136-57. doi: 10.1364/AO.50.001136.

National Ignition Facility system alignment.

Burkhart SC, Bliss E, Di Nicola P, Kalantar D, Lowe-Webb R, McCarville T, Nelson D, Salmon T, Schindler T, Villanueva J, Wilhelmsen K.

Source

Lawrence Livermore National Laboratory, California 94551, USA. burkhart1@llnl.gov

Abstract

The National Ignition Facility (NIF) is the world’s largest optical instrument, comprising 192 37?cm square beams, each generating up to 9.6?kJ of 351?nm laser light in a 20?ns beam precisely tailored in time and spectrum. The Facility houses a massive (10?m diameter) target chamber within which the beams converge onto an ?1?cm size target for the purpose of creating the conditions needed for deuterium/tritium nuclear fusion in a laboratory setting. A formidable challenge was building NIF to the precise requirements for beam propagation, commissioning the beam lines, and engineering systems to reliably and safely align 192 beams within the confines of a multihour shot cycle. Designing the facility to minimize drift and vibration, placing the optical components in their design locations, commissioning beam alignment, and performing precise system alignment are the key alignment accomplishments over the decade of work described herein. The design and positioning phases placed more than 3000 large (2.5?m×2?m×1?m) line-replaceable optics assemblies to within ±1?mm of design requirement. The commissioning and alignment phases validated clear apertures (no clipping) for all beam lines, and demonstrated automated laser alignment within 10?min and alignment to target chamber center within 44?min. Pointing validation system shots to flat gold-plated x-ray emitting targets showed NIF met its design requirement of ±50??m rms beam pointing to target chamber. Finally, this paper describes the major alignment challenges faced by the NIF Project from inception to present, and how these challenges were met and solved by the NIF design and commissioning teams.

Rev Sci Instrum.  2010 Oct;81(10):10D325.

The National Ignition Facility neutron time-of-flight system and its initial performance (invited).

Glebov VY, Sangster TC, Stoeckl C, Knauer JP, Theobald W, Marshall KL, Shoup MJ 3rd, Buczek T, Cruz M, Duffy T, Romanofsky M, Fox M, Pruyne A, Moran MJ, Lerche RA, McNaney J, Kilkenny JD, Eckart MJ, Schneider D, Munro D, Stoeffl W, Zacharias R, Haslam JJ, Clancy T, Yeoman M, Warwas D, Horsfield CJ, Bourgade JL, Landoas O, Disdier L, Chandler GA, Leeper RJ.

Source

Laboratory for Laser Energetics, University of Rochester, 250 East River Road, Rochester, New York 14623, USA. vgle@lle.rochester.edu

Abstract

The National Ignition Facility (NIF) successfully completed its first inertial confinement fusion (ICF) campaign in 2009. A neutron time-of-flight (nTOF) system was part of the nuclear diagnostics used in this campaign. The nTOF technique has been used for decades on ICF facilities to infer the ion temperature of hot deuterium (D(2)) and deuterium-tritium (DT) plasmas based on the temporal Doppler broadening of the primary neutron peak. Once calibrated for absolute neutron sensitivity, the nTOF detectors can be used to measure the yield with high accuracy. The NIF nTOF system is designed to measure neutron yield and ion temperature over 11 orders of magnitude (from 10(8) to 10(19)), neutron bang time in DT implosions between 10(12) and 10(16), and to infer areal density for DT yields above 10(12). During the 2009 campaign, the three most sensitive neutron time-of-flight detectors were installed and used to measure the primary neutron yield and ion temperature from 25 high-convergence implosions using D(2) fuel. The OMEGA yield calibration of these detectors was successfully transferred to the NIF.

Science.  2010 Mar 5;327(5970):1228-31. Epub 2010 Jan 28.

Symmetric inertial confinement fusion implosions at ultra-high laser energies.

Glenzer SH, MacGowan BJ, Michel P, Meezan NB, Suter LJ, Dixit SN, Kline JL, Kyrala GA, Bradley DK, Callahan DA, Dewald EL, Divol L, Dzenitis E, Edwards MJ, Hamza AV, Haynam CA, Hinkel DE, Kalantar DH, Kilkenny JD, Landen OL, Lindl JD, LePape S, Moody JD, Nikroo A, Parham T, Schneider MB, Town RP, Wegner P, Widmann K, Whitman P, Young BK, Van Wonterghem B, Atherton LJ, Moses EI.

Source

Lawrence Livermore National Laboratory, Post Office Box 808, Livermore, CA 94551, USA. glenzer1@llnl.gov

Abstract

Indirect-drive hohlraum experiments at the National Ignition Facility have demonstrated symmetric capsule implosions at unprecedented laser drive energies of 0.7 megajoule. One hundred and ninety-two simultaneously fired laser beams heat ignition-emulate hohlraums to radiation temperatures of 3.3 million kelvin, compressing 1.8-millimeter-diameter capsules by the soft x-rays produced by the hohlraum. Self-generated plasma optics gratings on either end of the hohlraum tune the laser power distribution in the hohlraum, which produces a symmetric x-ray drive as inferred from the shape of the capsule self-emission. These experiments indicate that the conditions are suitable for compressing deuterium-tritium-filled capsules, with the goal of achieving burning fusion plasmas and energy gain in the laboratory.

Rev Sci Instrum.  2009 Jun;80(6):063104.

NIF unconverted light and its influence on DANTE measurements.

Girard F, Suter L, Landen O, Munro D, Regan S, Kline J.

Source

CEA, DAM, DIF, F-91297 Arpajon, France.

Abstract

NIF laser facility produces 1053 nm light and a fundamental requirement for NIF is to give up to 1.8 MJ of 351 nm light for target physics experiments. The 351 nm light is provided by frequency tripling the 1053 nm light in nonlinear crystals in the final optics assembly, just before the laser light enters the target chamber. Since this tripling process is not 100% efficient, unconverted light from the conversion process also enters the chamber. This unconverted light does not directly hit the target but it can strike target support structures at average intensities of few TW/cm2 where it can generate unwanted, background soft x-rays that are measured by the soft x-ray diagnostic DANTE installed on the NIF target chamber. This diagnostic quantifies the x-radiation intensity inside the hohlraum by measuring the x-ray flux coming from the target’s laser entrance hole. Due to its centimeter wide field of view, it integrates x-ray emission from both the flux exiting a hohlraum laser entrance hole and from the target support structure irradiated by residual 1omega and 2omega unconverted light. This work gives quantitative evaluations of the unconverted light for the first time and the effects on DANTE measurements for the future NIF tuning experiment called “Shock timing.” Emission spectra are significantly modified leading to an overestimation of radiative temperature during the foot of the laser pulse since background x-rays are predominant in first two DANTE channel measurements. Mitigations of these effects by coating silicon paddle with plastic, using a smaller collimator to reduce DANTE field of view or eliminating DANTE channels in the analysis have been investigated.

Rev Sci Instrum.  2008 Oct;79(10):10E931.

Using x-rays to test chemical vapor deposited diamond detectors for areal density measurement at the National Ignition Facility.

Dauffy LS, Koch JA, Tommasini R, Izumi N.

Source

Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94551, USA. dauffyl@llnl.gov

Abstract

At the National Ignition Facility (NIF), 192 laser beams will compress a target containing a mixture of deuterium and tritium that will release fusion neutrons, photons, and other radiation. Diagnostics are being designed to measure this emitted radiation to infer crucial parameters of an ignition shot. Chemical vapor deposited (CVD) diamond is one of the ignition diagnostics that will be used as a neutron time-of-flight detector for measuring primary (14.1 MeV) neutron yield, ion temperature, and plasma areal density. This last quantity is the subject of this study and is inferred from the number of downscattered neutrons arriving late in time, divided by the number of primary neutrons. We determine in this study the accuracy with which this detector can measure areal density when the limiting factor is detector and electronics saturation. We used laser-produced x-rays to reproduce NIF signals in terms of charge carrier density, time between pulses, and amplitude contrast and found that the effect of the large pulse on the small pulse is at most 8.4%, which is less than the NIF accuracy requirement of +/-10%.

Appl Opt.  2008 Apr 1;47(10):1387-8; discussion 1384-6.

Comment on “National Ignition Facility laser performance status”.

Bodner SE.

Source

sebodner@mailaps.org

Abstract

The National Ignition Facility (NIF) laser has not yet achieved two of the stated requirements needed for testing and evaluating ignition targets. The laser focal spot size is more than a factor of 2 too large, and the laser bandwidth is more than a factor of 2 too small.

Appl Opt.  2007 Jun 1;46(16):3276-303.

National Ignition Facility laser performance status.

Haynam CA, Wegner PJ, Auerbach JM, Bowers MW, Dixit SN, Erbert GV, Heestand GM, Henesian MA, Hermann MR, Jancaitis KS, Manes KR, Marshall CD, Mehta NC, Menapace J, Moses E, Murray JR, Nostrand MC, Orth CD, Patterson R, Sacks RA, Shaw MJ, Spaeth M, Sutton SB, Williams WH, Widmayer CC, White RK, Yang ST, Van Wonterghem BM.

Source

Lawrence Livermore National Laboratory, Livermore, CA 94551, USA. haynam1@llnl.gov

Abstract

The National Ignition Facility (NIF) is the world’s largest laser system. It contains a 192 beam neodymium glass laser that is designed to deliver 1.8 MJ at 500 TW at 351 nm in order to achieve energy gain (ignition) in a deuterium-tritium nuclear fusion target. To meet this goal, laser design criteria include the ability to generate pulses of up to 1.8 MJ total energy, with peak power of 500 TW and temporal pulse shapes spanning 2 orders of magnitude at the third harmonic (351 nm or 3omega) of the laser wavelength. The focal-spot fluence distribution of these pulses is carefully controlled, through a combination of special optics in the 1omega (1053 nm) portion of the laser (continuous phase plates), smoothing by spectral dispersion, and the overlapping of multiple beams with orthogonal polarization (polarization smoothing). We report performance qualification tests of the first eight beams of the NIF laser. Measurements are reported at both 1omega and 3omega, both with and without focal-spot conditioning. When scaled to full 192 beam operation, these results demonstrate, to the best of our knowledge for the first time, that the NIF will meet its laser performance design criteria, and that the NIF can simultaneously meet the temporal pulse shaping, focal-spot conditioning, and peak power requirements for two candidate indirect drive ignition designs.