A special series of Physics of Plasmas papers by National Ignition Campaign (NIC) researchers published online on June 1 discuss the work now under way to prepare NIF for fusion ignition shots.
In an introductory article, "On the threshold of initiating ignition experiments," NIF Director Ed Moses and Chief Scientist John Lindl describe three key requirements for achieving ignition: improving understanding of some of the ignition physics and material properties that will exist during fusion experiments, resolving uncertainties in the physics models, and determining progress toward ignition.
The first paper in the series, by Steve Haan and colleagues, introduces the ignition threshold factor (ITF), the criterion being used to establish requirements on the laser, targets, and experiments that will result in the required imploded fuel conditions. In the second paper, Nino Landen and colleagues report on the experimental approach the researchers are using to optimize the principal implosion input variables in the presence of physics uncertainties, with the goal of substantially increasing the probability of ignition on NIF. The third paper, by John Edwards and colleagues, discusses the use of cryogenically layered targets to assess progress toward achieving the compressed fuel conditions required for ignition.
According to Moses and Lindl, the series of "mini-tuning" campaigns now under way on NIF, each involving 20 to 30 shots, will enable researchers "to determine if we achieve the expected improvement in performance as the precision of the tuning improves. This...approach enables the NIC to incorporate results from ongoing experiments into modifications of the...specifications for aspects of the laser performance, target fabrication, or the diagnostics in order to achieve the performance required for ignition."
One year after office moves began, Lawrence Livermore National Laboratory (LLNL)'s High-Energy Density Science (HEDS) "Campus" celebrated its official opening on June 30 with a ribbon-cutting ceremony and open house.
NIF Director Ed Moses said the event was "our way of acknowledging all of those involved in making the HEDS Campus vision a reality." Moses gave special thanks to Chris Keane, director of the NIF User Office, and Valerie Roberts, deputy principal associate director for operations, for conceiving and carrying out the integration of about 400 people working in HED science into a cohesive facility.
LLNL Deputy Director Tom Gioconda said the facility's employees will be "planning the future," while Bill Goldstein, associate director of Physics and Advanced Technologies, said the new facility will be "making the most of what the Lab is capable of doing, and is great at doing." Bruce Goodwin, principal associate director for Weapons and Complex Integration, praised the recent weapons science work on NIF and said the HEDS facility "will make that even better."
The 'Campus' comprises HEDS and fusion researchers from LLNL, along with collaborators working on the National Ignition Campaign and other Department of Energy HEDS activities, and university researchers associated with the Science Use of NIF and Jupiter Laser Facility academic programs.
Areal density – a measure of the combined thickness and density of the fuel shell in an ignition target – is an important factor in the final configuration of the fuel for obtaining ignition and burn in an inertial confinement fusion (ICF) experiment. Abbreviated ρr (rho-r), areal density is a function of how much energy is absorbed by the fuel and the accuracy of target conditions during implosion, or how well the capsule is tuned. By detecting the scattering of neutrons produced in the hot spot as they pass through the surrounding shell, scientists can calculate a target's areal density, which is essential for determining whether the capsule has enough mass to sustain the fusion reaction.
Diagnostic equipment recently installed on NIF, the Neutron Time-of-Flight (nTOF) instruments and the Neutron Imaging System, have been successfully collecting data during the recent shock timing and tuning campaigns as well as this month's deuterium-tritium (DT) experiments (see June Project Status). The nTOF, developed for NIF in collaboration with the Laboratory for Laser Energetics at the University of Rochester, measures the total neutron emission, temperature of the fuel, time of peak emission (bang time), and areal density of the compressed fuel.
The Neutron Imaging System, developed jointly by Los Alamos National Laboratory and LLNL, provides information about the areal density of fuel in the various regions of the capsule implosion by imaging both high-energy (14 million electron-volts, or 14 MeV) neutrons and "down-scattered" neutrons with energies in the range of 10 to 12 MeV. By calculating the down-scatter ratio (DSR) – the number of neutrons from 10 to 12 MeV divided by the number of neutrons between 13 and 15 MeV – researchers can infer the areal density.
LLNL's plans for developing ribbon-shaped fibers to improve power scaling in continuous wave fiber lasers were described at the June 6-10 Advanced High Power Lasers Conference in Santa Fe, NM. Led by Jay Dawson and colleagues in the Photon Science & Applications Program and the Lasers and Optics Research Center at the U.S. Air Force Academy, the project aims to significantly increase the power of fiber lasers by changing the shape of the waveguide from a circularly symmetric fiber to a rectangular, or ribbon-shaped, fiber (see February 2011 Photons & Fusion Newsletter).
The shape and size of the ribbon fiber was established through a combination of computer simulation and analytical modeling. Changing to a rectangular geometry significantly improves scalability, without optical damage.
The Serrated Light Illumination for Deflection-Encoded Recording (SLIDER), developed by John Heebner of NIF & Photon Science and Susan Haynes of LLNL's Engineering Technologies Division, has received a 2011 R&D 100 Award from R&D Magazine.
SLIDER is the world's fastest light deflector, capable of sweeping a beam of light at the rate of one resolvable spot every picosecond (trillionth of a second). In conjunction with an ordinary camera, the device can be used to record ultrafast events at picosecond timescales with long durations and high dynamic range. Former Lab employee Chris Sarantos also contributed to its development. For more information, see the LLNL news release and the April 2010 Photons & Fusion Newsletter.
A number of LLNL researchers gave presentations on NIC and on LLNL's Laser Inertial Fusion Energy (LIFE) concept at the 38th IEEE International Conference on Plasma Science (ICOPS) and 24th Symposium on Fusion Engineering (SOFE) held June 26-30 in Chicago.
On behalf of the NIC team, Joe Kilkenny gave an invited talk on the performance of the recent ignition-type implosions on NIF. Kilkenny described the implosion tuning campaign, which is aimed at optimizing target performance resulting in an ignition target that yields more fusion energy than the laser energy sparking the fusion reaction. Several NIC researchers also discussed commissioning the nuclear diagnostic instruments used on NIF to measure the performance of a burning capsule, including energy yield, temperature, and efficiency.
In an invited talk, Mike Dunne, NIF & Photon Science director for laser fusion energy, discussed progress on NIF and the development of a technology pathway for LIFE consistent with the needs of the electric power industry. He also participated in a June 27 SOFE Town Hall meeting on "Accelerating the Development of Fusion Power."
Dunne noted that many of the scientific and technological advances made under the NIF ignition program, coupled with ongoing developments in the laser, manufacturing and nuclear industries, are helping pave the way to the development of a LIFE power plant.
In another invited presentation, Jeff Latkowski and colleagues described the characteristics of the integrated LIFE target chamber design, including the ability to capture and transmit fusion energy, produce tritium fuel to replace that burned in previous targets, and enable operations at roughly 900 shots per minute.
Plans for a number of ground-breaking fundamental science experiments on NIF were reviewed by a Science on NIF Technical Review Committee meeting at the Laboratory from June 13 to 15. Among the research topics covered were the hydrodynamics of supernovae, pair plasma creation using NIF, nucleosynthesis, collisionless shocks, carbon and iron equation-of-state experiments, X-ray diffraction studies of compressed diamond, and matter at ultra-high densities. Also discussed were NIF diagnostics in support of science on NIF. The Committee was also provided an update on the progress of the National Ignition Campaign.
An International Atomic Energy Agency (IAEA) technical meeting on "Control, Data Acquisition, and Remote Participation for Fusion Research" was held in San Francisco from June 20 to 24. Sponsored by LLNL, NIF and the MIT Plasma Science & Fusion Center and hosted by NIF, the meeting presented and discussed new developments and perspectives in the areas of control, data acquisition, data management and remote participation for nuclear fusion research around the world. About 150 experts from IAEA member states and international organizations attended.
In a June 23 special session on inertial fusion energy chaired by NIF&PS' Larry Lagin, NIF Director Ed Moses and several NIF&PS researchers discussed NIF, NIC, LIFE, and the various control systems used to direct NIF's experiments and diagnostic equipment. NIF&PS researchers also made presentations and presented posters during the meeting describing workflow, data, and campaign management tools used in NIF; control system verification and validation; the laser pulse shaping system; target image and optics analysis systems; and other aspects of the NIF Integrated Computer Control System.
Modern lithium-ion battery technologies hold promise for powering the next generation of high-efficiency electric laser systems, such as the one proposed for LIFE, LLNL researchers reported in a June 22 presentation at the IEEE International Pulsed Power Conference in Chicago.
The researchers said recent improvements in battery power density, price, and laser diode manufacture and scale-up permit electrical laser systems to be upgraded for reliability, compactness, and operation at high repetition rates. Members of the LLNL team preparing the presentation, "Battery-Based Architectures for Applications in Lasers and Other Pulsed Power Systems," were Bill DeHope, Bill Clark, Glen James, Brent McHale, Bernie Merritt, and Anthony Rivera.
U.S. Representatives Zoe Lofgren (CA-16th District) and George Miller (CA-7th District) visited NIF on June 10. Rep. Lofgren is a member of the House Committee on Science, Space and Technology, and Rep. Miller is chairman of the Democratic Policy Committee. They received briefings on LIFE, toured NIF, and observed a shot from the NIF Control Room.
Rep. Lofgren was among 13 members of Congress who recently signed a letter to the leaders of the House Appropriations Subcommittee on Energy and Water Development advocating strong government funding for fusion energy research. "Fusion is one of a small number of truly base-load, sustainable, safe and secure energy options that can meet the scale of the national and global demand," the letter said. "The U.S. has a proud history of leading the world in innovation and technology development and we should aspire to be the world leader in fusion energy." The full text of the letter is available here.
Singer-songwriter Peter Gabriel and futurist Peter Schwartz visited NIF on June 9 and received a tour and a briefing on LIFE. Gabriel, who was performing in the Bay Area, became interested in NIF and fusion energy through his humanitarian work and his affiliation with Schwartz's Global Business Network and the forward-looking Long Now Foundation, where Schwartz is a member of the board of directors. After his tour, Gabriel autographed a photo with this message to the NIC team: "You are doing really inspiring work that will transform the world."