Photons & Fusion Newsletter

September 2011

UK and LIFE Agree to Collaborate on Laser Fusion

Lawrence Livermore National Laboratory has signed a memorandum of agreement with two long-term partners from the United Kingdom – the Rutherford Appleton Laboratory and the Atomic Weapons Establishment – to engage in joint research directed at the exploration of the challenges associated with the design, development and delivery of Laser Inertial Fusion Energy (LIFE) power plants.

Announced on Sept. 9 at the Royal Society of Science by David Willetts, UK Minister of Science and Technology, the agreement will allow the three entities to join forces to address the challenges of taking laser fusion from a NIF laboratory experiment to a widely available, commercialized energy source.

The Right Honourable David Willetts MP (left) and Ed Moses at the Royal Society of Science where an agreement was announced between LLNL, the Rutherford Appleton Laboratory, and the UK Atomic Weapons Establishment to engage in joint research to explore development and delivery of LIFE power plants. The poster in the background describes the European High Power Laser Energy Research Facility, or HiPER.

The agreement grew out of conversations between John Beddington, Chief Scientist of the United Kingdom, and Steve Koonin, Undersecretary of Energy for the DOE. The announcement was covered via BBC News World Service interviews and posted on the BBC website.

LLNL's Fiber Draw Tower Draws Its First Fiber

Pamela Divoky, project manager for NIF&PS Operations, checks on the installation of the 8.2-meter-tall Fiber Draw Tower in Bldg. 391.

The commissioning phase of the Laboratory's new Fiber Draw Tower began on Aug. 31 as the first strand of optical glass fiber was drawn at the facility. The strand demonstrated the 8.2-meter tower's capability to draw fibers ranging from 80 to 500 micrometers in diameter (see February 2011 Photons & Fusion Newsletter).

Planning for the tower began in January 2010. "This is a very complex and state-of-the-art machine," said project leader Jay Dawson, "and it was critical to ensure that all components and subsystems complied with all of our manufacturing and safety standards." The tower components arrived at LLNL in late June 2011 for installation in Bldg. 391. Dawson praised the team effort and cooperation "from a wide range of groups here at LLNL and NIF" that led to successful installation of the tower.

In conjunction with this work, the Photon Science & Applications Fiber Laser Group, led by Dawson, and the Lasers and Optics Research Center at the U.S. Air Force Academy collaborated to develop a code that can model photonic crystal fiber structures on LLNL supercomputers. The tower and associated modeling capability will allow scientists to make new waveguide designs within just a week or two, depending on the complexity of the design.

An example is photonic crystal fibers, now under development at LLNL, which will substantially increase the power of ribbon-shaped fiber lasers. Changing to a rectangular geometry significantly improves scalability without optical damage.

Liquid Deuterium Shock Timing Experiments

The first experiments to time multiple, spherically converging shock waves in cryogenically cooled liquid deuterium were described by NIC researchers in the cover article in the September issue of Physics of Plasmas (Phys. Plasmas 18, 092706 (2011); doi:10.1063/1.3640805).

Inertial confinement fusion (ICF) target designs use a sequence of shocks to compress the target before it implodes. To minimize the entropy acquired by the fuel, the strength and timing of these shocks is precisely set during a series of tuning experiments that adjust the shape of the laser pulse to achieve optimal conditions for ignition.

The experiments reported in the Physics of Plasmas article were conducted on the OMEGA laser facility at the University of Rochester. Using direct irradiation of the target, they produced a sequence of up to four shocks, whose strength and timing were designed so that later shocks overtake earlier ones to produce multiple shocked deuterium. The shocks coalesced about 200 microns into the deuterium, forming a single strong shock that converged toward the center of the target.

Using velocity interferometery to measure the velocity and timing of the shock waves, the researchers measured speeds of 25 to 135 kilometers per second (km/s) in continuous velocity profiles for up to four shocks. A velocity of 135 km/s was the highest shock velocity reported in cryogenic deuterium at the time of the experiments and corresponds to a pressure of about 25 megabars, or 25 million times Earth's atmospheric pressure.

The experiments demonstrated the ability to time and control shock waves to the precision needed for ignition experiments, and the technique has subsequently been applied to full-scale experiments to tune hohlraum-driven ignition targets on NIF, where shock velocities were measured up to about 150 km/s. The OMEGA experiments were also used to validate the radiation-hydrodynamic codes used to design direct-drive ICF targets for OMEGA and NIF.

Tom Boehly of the University of Rochester's Laboratory for Laser Energetics (LLE) was lead author of the article. Also contributing were LLNL researchers Peter Celliers, Damien Hicks, Maria Barrios, Dayne Fratanduono, and Gilbert (Rip) Collins, along with LLE researchers Valery Goncharov, Wolf Seka, Suxing Hu, John Marozas, and David Meyerhofer.

NIC, LIFE Featured at IFSA 2011

A wide variety of presentations describing recent progress on the National Ignition Campaign and the LIFE concept were featured at the Seventh International Conference on Inertial Fusion Sciences & Applications (IFSA), held Sept. 12 to 16 in Bordeaux, France. Co-chaired by NIF Director Ed Moses and attended by about 600 inertial fusion and high-energy-density physics researchers from around the world, the conference included nearly 50 papers and dozens of posters by the NIC and LIFE team researchers.

Featured talks included a plenary address by Moses about NIF's future as an international high-energy-density science and inertial fusion user facility, and a plenary talk by NIF & Photon Science Chief Scientist John Lindl, with Nino Landen and John Edwards, discussing the goals and progress of the ignition campaign.

LIFE was discussed in presentations covering LIFE drivers and compact line replaceable units, the LIFE target design, gain requirements for a LIFE power plant, and other topics. Also discussed were NIF laser performance and diagnostics, the results of the recent tuning and cryogenic layered target experiments, laser-plasma interactions and target hydrodynamics, experimental capabilities on NIF, and NIF as a national user facility.

Bruce Remington Receives Edward Teller Medal

NIF&PS physicist Bruce Remington has been awarded the 2011 Edward Teller Medal in recognition of his pioneering research and leadership in the use of lasers for HED physics, laboratory astrophysics, and inertial confinement fusion (ICF) research.

Bruce Remington (left) is presented the 2011 Edward Teller Medal by Robert Kauffman of NIF on behalf of the American Nuclear Society during the IFSA conference in Bordeaux, France.

Sponsored by the American Nuclear Society, the medal was awarded to Remington and French physicist Christine Labaune, Director of the Institute for Lasers and Plasmas at Ecole Polytechnique-Université in Bordeaux. In recognition of the honor, Remington and Labaune presented Teller Lectures on the final day of the IFSA conference; Remington's lecture was titled, "HED experiments for ICF, astrophysics, and materials science."

Remington has been a staff physicist at LLNL in the ICF Program since 1988, and a group leader since 1996. He and his group work on laser-driven HED fluid instabilities, HED laboratory astrophysics, and solid-state dynamics at high pressures and strain rates. He received his BS degree from Northern Michigan University in 1975 and his PhD degree in nuclear physics from Michigan State University in 1986. Remington is a recipient of the Excellence in Plasma Physics Award from the American Physical Society Division of Plasma Physics for his work on ablation-front Rayleigh-Taylor instabilities. He is a Fellow of the American Physical Society.

U.S. and Russia Hold Joint ICF Workshop

Nine representatives from two Russian nuclear and high-energy-density (HED) physics laboratories joined colleagues from LLNL, Los Alamos and Sandia national laboratories, and U.S. Department of Energy headquarters in an inertial confinement fusion (ICF) technical workshop on Aug. 31 and Sept. 1 at the Laboratory.

The researchers, representing the Russian Federal Nuclear Center-All-Russian Research Institute of Experimental Physics (RFNC-VNIIEF) and the RFNC-All-Russian Scientific Research Institute of Technical Physics (RFNC-VNIITF), described their respective countries' ICF and HED capabilities, heard presentations on the status of the National Ignition Campaign and the LLNL Laser Inertial Fusion Energy (LIFE) concept, and discussed the current status and plans for fusion and fusion/fission hybrid energy systems. The visitors also toured NIF. The workshop concluded with a discussion of next steps in the collaboration.

Inside the Master Oscillator Room, NIF Director Ed Moses (right) describes the master oscillator to Russian researchers during their Aug. 31 tour of NIF. The master oscillator generates the initial low-energy laser pulse that is split into 192 beams and amplified more than a quadrillion times in the Main Laser System.

MEGa-ray Test Station Described at Conference

NIF&PS researcher Felicie Albert discussed the development of the X-band test station for LLNL's mono-energetic gamma-ray (MEGa-ray) source at the International Particle Accelerator Conference (IPAC'11), held Sept. 4 to 9 in San Sebastian, Spain.

The test station, now under construction, is a collaboration between the Laboratory and the Stanford Linear Accelerator Laboratory. Optimizing MEGa-Ray's electron source has the potential to increase its gamma-ray beam brightness by several orders of magnitude.

Consisting of an X-band photoinjector, single accelerator section, and beam diagnostics, the test station will produce narrow-bandwidth gamma rays to increase the total flux at 120 Hz, while researching methods to raise the effective repetition rate of the machine to greater than 1,000 Hz. The effective repetition rate will be increased by operating the RF photoinjector in a multi-bunch mode, accelerating multiple electron bunches in each RF pulse.

In a second presentation at IPAC'11, Albert described potential sources of spectral broadening optimization to enable the use of MEGa-ray sources in applications such as nuclear resonance fluorescence to detect specific nuclei and isotopes.

Radiochemical Gas Analysis System Installed

The first phase of the Radiochemical Analysis of Gaseous Samples (RAGS) noble-gas collection diagnostic from Sandia National Laboratory has been installed in the NIF.

The Sandia RAGS (Radiochemical Analysis of Gaseous Samples) chemical analysis equipment was recently installed in the RAGs area in Bldg. 581. Commissioning of the system is scheduled to begin by the end of this month.

Radiochemical diagnostic techniques, such as analysis of solid- and gas-phase capsule debris, will help characterize NIF ignition experiments. Tracers added to NIF target capsules will undergo nuclear reactions. These will then be collected and purified for nuclear counting by the RAGS system.

Samples in the gas phase offer the most direct method of collection by simply pumping out the large target chamber following a NIF shot. This technique can help researchers learn about what processes take place inside the capsule (such as neutron scattering and mix) by measuring the number of neutron- and charged-particle activations that occur. Measuring the isotopic ratios of noble-gas products from neutron-induced reactions can provide a good measure of the areal density of the NIF capsule.

Future RAGS capabilities include in situ counting of gamma-emitting species and the ability to purify and cryogenically separate xenon, krypton, and possibly argon and neon.

LLNL and NIF Host Ultrafast Optics Conference

The Laboratory and the NIF & PS Directorate hosted the Eighth International Conference on Ultrafast Optics from Sept. 26 to 30 in Monterey, CA. About 130 users and developers of ultrafast optical technologies gathered to report on the state of the art with respect to the generation, amplification, and measurement of picosecond (trillionth of a second), femtosecond (quadrillionth of a second), and attosecond (quintillionth of a second) optical pulses.

The study of ultrafast phenomena has found widespread use in physics, chemistry, engineering, and medicine. Keynote, invited, and contributed talks and poster presentations covered such topics as ultra-high peak-power laser systems, pulse amplification, novel materials for ultra-fast laser sources, pulse shaping, and technology development for NIF's Advanced Radiographic Capability, which will provide multi-frame x-ray imaging during NIF ignition experiments.

In an invited "overview" talk, NIF&PS Chief Technology Officer Chris Barty, conference co-chair and founder of the biennial meeting, discussed the National Ignition Campaign and progress towards demonstrating fusion ignition in the laboratory. More than 60 participants also toured NIF on the final day of the conference.

LLNL Gratings Enable Petawatt Laser System

Representatives of the European Extreme Light Infrastructure (ELI) project visited LLNL on Sept. 22 to inspect five gold over-coated meter-class diffraction gratings fabricated at the Laboratory. The gratings will be used for pulse compression in the Apollon laser, a multi-petawatt (trillion-watt)-class ultrafast laser system being built in Palaiseau, France, by the Centre National de la Recherche Scientifique (National Center for Scientific Research) along with partner organizations.

Jean-Michel Boudenne (left) and Catherine Le Blanc of the French Center for Scientific Research, and Mathias Le Pennec of the optical instrument company ARDOP, Inc., with the LLNL diffraction gratings to be used in the Apollon ten-petawatt laser.

Apollon is one of three multi-petawatt lasers now under development in Europe. These lasers will point the way to plans for the ELI, an even more ambitious ultrafast, 200-petawatt laser, which will conduct experiments at the frontiers of physics, including such fields as particle physics, nuclear physics, gravitational physics, nonlinear field theory, ultrahigh-pressure physics, astrophysics and cosmology.

The gratings were designed and made by the Photon Science & Applications Diffractive Optics Group – Jerry Britten, Hoang Nguyen, Mike Aasen, Cindy Larson, Tom Carlson, Curly Hoaglan, James Nissen and Jim Peterson – with support from the Vacuum Process Lab's Phil Ramsey and Ron Foreman.

Path to Ignition Described at QuAMP 2011

LLNL researcher Debra Callahan discussed recent NIF experiments to tune target capsules for ignition at the International Conference on Quantum, Atomic, Molecular and Plasma Physics (QuAMP 2011), held Sept. 18-22 in Oxford, UK. QuAMP 2011 was one of a series of biennial meetings of the Division of Atomic, Molecular, Optical and Plasma Physics of the Institute of Physics.

Achieving ignition requires tuning the shape of the implosion, tuning the series of four shocks to accelerate the shell while keeping it on a low adiabat (heat transfer), tuning the laser pulse to achieve the required peak velocity, and controlling hydrodynamic mix of ablator material into the fuel, Callahan said.

In the spring of 2011, the National Ignition Campaign focused on improving the adiabat of the fuel, which is needed to achieve adequate compression. These experiments led to an increase in the areal density (ρr) of the shell by more than 50 percent (ρr is a measure of the combined thickness and density of the fuel shell around an igniting target). "The current campaign is focused on getting high velocity while maintaining good compression and shape," she said.

CEA and LLNL Researchers Discuss Radiation Effects

Seven researchers from the Commissariat à l'Energie Atomique (CEA), the French Atomic Energy Commission, met with LLNL staffers from Sept. 28 to 30. The meeting, hosted by NIF&PS' Trish Baisden, was arranged to exchange information and ideas on managing and mitigating electromagnetic pulse (EMP) and neutron radiation effects on hardware in large, high-energy, high-power laser facilities such as NIF and the Laser Megajoule, the French equivalent of NIF under construction by the CEA near Bordeaux.

Phil Datte describes neutron vulnerability assessments at the LLNL/CEA radiation effects workshop.

Dave Eder, Charlie Brown and Jim Watson presented modeling and experiments done on NIF and LLNL's Titan laser to understand the effects of EMP generation and methods for mitigating those effects. The remainder of the meeting focused on hardening the two facilities and their target diagnostics against neutron exposures from high-yield experiments.

Discussions covered modeling of the neutron flux in the facilities, testing of hardware to assess potential vulnerability to neutrons, and strategies for developing new radiation-hardened diagnostics and other equipment. Hesham Khater, Phil Datte and Mark Jackson presented the work of the LLNL neutron working group. Several areas of common interest and potential synergy were identified at the meeting, which is expected to lead to continuing discussions between CEA and LLNL researchers.

CEA researchers attending the meeting were Geneviève Chabassier, Jean-Claude Gommé, Jacques Baggio, Sylvain Girard, Julien Gazave, Sebastien Bazzoli, and Jean-Luc Bourgade.