Photons & Fusion Newsletter

October 2011

A New Mission for LLNL's 'Peening Laser'

NIF and Photon Science personnel, working closely with NIF Professor at UCLA Christoph Niemann, recently completed the successful transfer of the LLNL-constructed, award-winning "peening laser" to UCLA. This short-pulse laser, owned by the U.S. Navy Space and Naval Warfare Systems Center, will be coupled to UCLA's 20-meter-long Large Plasma Device to create a premier laser facility for simulations of explosive space and astrophysical phenomena.

Derek Schaeffer (left), a physics graduate student at UCLA, and Assistant Researcher Carmen Constantin of the UCLA High Energy Density Plasma Physics group examine the peening laser shortly after its arrival from LLNL.

The laser will be used to examine in detail the physics of "collisionless shocks" present in astrophysical phenomena such as solar flares and supernova remnants. Addition of the laser "is going to have a huge impact on our research program," Niemann said. Added NIF User Office Director Chris Keane: "Transfer of the laser to UCLA demonstrates the continuing commitment of NIF and the U.S. Navy to fundamental academic research and the training of students. We appreciate the Navy's support of this transfer."

NIF&PS employees involved in the transfer include Tony Ladran (formerly of Photon Science & Applications and now with Weapons and Complex Integration); Kim Hallock, Chris Keane, and Bonnie McDonald (NIF User Office); and Mary Norton and Paul Wegner (NIF Programs).

The "peening laser," based on a NIF neodymium/glass laser design, was commissioned by the U.S. Navy in the early 1990s. After several modifications, it was reconfigured into a short-pulse 10-nanosecond laser, which became the basis for a commercial peening laser system developed through a cooperative research and development agreement with Metal Improvement Corporation. Currently used to strengthen jet engine fan blades and in airframe manufacturing, the commercial peening laser earned three R&D 100 awards from 1998 to 2003.

Mitigating Raman Scattering in Laser Crystals

Potassium dihydrogen phosphate (KDP) and deuterated KDP (DKDP) crystals are used for frequency conversion and beam control in high-power, large-aperture laser systems such as NIF. These materials are also most susceptible to transverse stimulated Raman scattering (TSRS) compared to other materials used in inertial confinement fusion-class laser systems due to their relatively higher strength of their main Raman active vibrational mode. TSRS can occur when large-aperture optical components are exposed to high irradiance and high fluence (energy per unit area) laser pulses. TSRS can cause laser energy loss and potentially damage the edges of the optic and adjacent components.

To gain a better understanding of TSRS, LLNL researchers measured the spontaneous Raman scattering cross-sections in representative KDP and DKDP samples at different wavelengths using that of water as a reference. This enabled them to experimentally determine all needed parameters to estimate the TSRS gain in KDP and DKDP and to evaluate the upper limit of the materials' tolerance to SRS after operational parameters and material specifications are considered.

Reporting on their findings in the October issue of Optics Express, the researchers said that to prevent build-up of the Raman scattered light from multiple traversals through the crystal in a long laser pulse, reflectivity at all crystal edges should be reduced. For example, the crystal edges and corners should be chamfered (cut at an angle) and beveled in a compound manner to prevent multiple passes of side-scattered light at all wavelengths. Stavros Demos was lead author on the paper; also contributing were Rajesh Raman, Steven Yang, Raluca Negres, Kathleen Schaffers, and Mark Henesian.

Information Technology Described at Open World

Information technology used on NIF was described during the Oracle Open World conference, held Oct. 2 to 6 in San Francisco.

In a talk titled, "Building a Virtual Computing Platform for Fusion Energy Research," Tim Frazier, Philip Adams, John Fisher and Adam Talbot discussed the 2,500 servers and 400 network devices that provide the foundation for NIF's real-time control system and Experimental Data Archive. The presentation described NIF's use of Oracle Virtual Machine in connection with the tools, processes and procedures that manage the computing platform that supports the National Ignition Campaign (NIC) experimental campaigns.

Frazier and his colleagues also discussed Oracle Enterprise Manager's cloud management capabilities, the use of Oracle 11gR2 as a platform for managing fusion energy research data, and utilities developed in-house by the NIF team.

International Laser Operations Workshop

NIF operations managers Leon Berzins, Tom Kohut and Terry Land gave presentations on NIF's status and diagnostics and recent NIC experimental results at the 8th International Laser Operations Workshop, held at the UK Atomic Weapons Establishment's Orion Laser Facility. The workshop, held every 18 months to two years, brings together operations managers from large laser facilities in the United States, the UK and France.

After presentations on facility status and operational issues, breakout sessions were held on such topics as safety, short-pulse laser operations, target diagnostics, training, maintenance and scheduling. The Laboratory is scheduled to host the next workshop in May of 2013.

MEGa-ray Technology Discussed

NIF&PS Chief Technology Officer Chris Barty presented an invited talk titled, "Nuclear Photonics with Laser-based Gamma-Rays" on Oct. 12 at the IEEE Photonics 2011 Conference. Barty said MEGa-rays (Mono-Energetic Gamma-rays) of unprecedented peak brilliance can be created via the optimized interaction of laser light with relativistic electrons. MEGa-ray sources enable the excitation and manipulation of the nucleus with photons, or nuclear photonics, and can access a new area of interaction with matter that has not previously been explored.

10th Anniversary of NIF Milestones Celebrated

Several hundred NIF&PS employees remembered and recognized the "Spirit of 2001" on Oct. 26 in a celebration commemorating the 10th anniversary of the completion of the NIF building, completion of the Cluster 3 laser beampath in Laser Bay 2, installation of the first of more than 6,000 line replaceable units (LRUs), and creation of the first laser light in the NIF master oscillator room (MOR), all in the fall of 2001.

NIF & Photon Science employees gather on the lawn between Bldgs. 481 and 482 for a commemoration of four NIF construction project milestones completed in the fall of 2001.

NIF Director Ed Moses said the four milestones marked a turning point in the NIF construction project after a period of setbacks and waning confidence. "The project had been on its back," Moses said, "and we were crawling our way back. Could we finish the first cluster on Oct. 23? Could we get the first LRU installed and first light out of the MOR? We did it, in a period of an incredible three weeks, and we emerged as a project and a team that was going to make this (NIF) happen. We were off, and there was no looking back."

Moses read the inscription on the back of a wine bottle commemorating the "contributions and spirit of the teams from 2001 into perpetuity. The essence of this award embodies the highest levels of teamwork, commitment and dedication to excellence. The fruit from the labor of these sustained accomplishments flourished into scientific discovery towards Bringing Star Power to Earth."

Synchrotron Aids Study of Fused Silica Breakdown

LLNL and Lawrence Berkeley National Laboratory (LBNL) researchers have used synchrotron radiation microscopy at LBNL's Advanced Light Source to gain new insights into the breakdown of fused silicon dioxide (a-SiO2) surfaces caused by nanosecond-pulse laser energy.

Because of its unique optical and thermal properties, fused silica is a key element in ultraviolet-resistant optical assemblies for inertial confinement fusion laser systems such as NIF. In an Applied Physics Letters paper published online on Oct. 13, the researchers described how they used synchrotron-based Fourier transform infrared and photoluminescence microscopy to probe fused silicon dioxide structural transformations as a function of laser pulse lengths.

LLNL's Manyalibo Matthews was the paper's lead author; also contributing were Christopher Carr and Rajesh Raman from LLNL and Hans Bechtel from LBNL.

NIF's Role in Stockpile Stewardship Discussed

Ed Moses described recent experiments on NIF in support of the National Nuclear Security Administration's High Energy Density Stewardship Science (HEDSS) program at a Nuclear Explosives Design Physics Conference held from Oct. 17 to 21.

Moses said NIF has completed nearly 150 target experiments for the HEDSS program in the areas of radiation transport and material dynamics at high pressure in the solid state, as well as fundamental science and other national security missions. A series of 34 experiments were successfully executed over a 27-day period earlier this year, demonstrating NIF's ability to perform precise experiments in new regimes of interest to HEDSS.

In a separate presentation at the conference by Peter Young and colleagues from LLNL and the UK's Atomic Weapons Establishment, the experimental campaign to measure radiation transport through evolving density profiles on NIF was described. The talk reviewed the campaign requirements and how they affected the experimental design. The researchers said the success of the campaign relied on a large number of people working towards carefully prescribed requirements on targets, diagnostics and the NIF laser facility.

LLNL's Role in Fusion Energy Described

Moses was also a featured speaker at the annual meeting of the Southern States Energy Board, held Oct. 15 to 17. Moses discussed technical aspects of LLNL's Laser Inertial Fusion Energy (LIFE) power plant design. He said more than 30 major vendors in such fields as construction and engineering, optics, semiconductors, and controls have been engaged in the LIFE design.

Tom Anklam discussed NIF and LIFE technology on Oct. 17 in a keynote talk at the 15th International Conference on Fusion Reactor Materials, sponsored by the U.S. Department of Energy's Office of Fusion Energy Sciences. Anklam's talk described recent National Ignition Campaign tuning experiments to optimize NIF target implosions. Anklam noted that LIFE is designed to employ commercially available technology and materials, and he said the fusion chamber in a pilot LIFE power plant would be able to use conventional steel and not have to wait for development of new radiation-resistant alloys.