The Secretary of Energy Advisory Board
National Ignition Facility Laser System Task Force

Members:
John P. McTague (Chairman)
Andrew Athy (Chairman, SEAB)
Robert Byer
Gail McCarthy
Lawrence Papay
Burton Richter
Rochus Vogt
John Warlaumont

c/o Betsy Mullins, Executive Director, SEAB
U.S. Department of Energy
1000 Independence Avenue, SW
Washington, DC 20585

November 17, 1999

Members of the NIF Laser System Task Force:

On behalf of the Natural Resources Defense Council, Inc. (NRDC), we are submitting written comments to the Secretary of Energy Advisory Board National Ignition Facility Laser System Task Force (herein referred to as the "SEAB NIF Task Force"). The Secretary of Energy has requested that the SEAB NIF Task Force consider "at a minimum: the engineering viability of the proposed assembly and activation method; the assembly and installation cleanliness protocols; the management structure; and the adequacy of the cost estimating methodology." The National Ignition Facility (NIF) project is troubled by a number of significant technical problems in addition to the problem of clean room status. Because these additional problems facing the NIF project are outside the minimum Terms of Reference, recommendations based solely on these minimum Terms of Reference cannot serve as an adequate basis for advising the Secretary on the future of the NIF project.

Four problems facing the NIF project in addition to clean room issues are in the areas of: 1) amplifier glass fabrication; 2) anti-reflective optical coatings; 3) spatial filters; and 4) ignition target fabrication.

1) Laser Amplifier Glass: The Schott company with manufacturing facilities in Pennsylvania and the Hoya company in California are currently contracted to fabricate the large slabs of amplifier glass for the NIF project. Schott and Hoya also fabricated the amplifier glass for NIF’s predecessor facility, Nova. The initial operating experience from Nova indicated that platinum inclusions in the glass were at an unacceptably high density, and the effect was that Nova could not run at the planned energy fluence. Subsequently, Schott and Hoya improved the glass fabrication technique for Nova which involved a slow, cooling/conditioning process after the glass was poured.

This amplifier glass fabrication technique demonstrated on Nova is not planned for the NIF because it would be too costly and time-consuming for the NIF’s greater glass requirements. Rather, the NIF project entails an exploratory glass fabrication technique called "continuous-melting" or "continuous-pouring." LLNL first gave Schott and Hoya moneys to build prototype laser glass factories, to let them compete and see which one did a better job. Neither prototype factory produced glass meeting all of the NIF specifications, but both companies assured LLNL that they understood the problems and could fix them. With those contractor promises, and Livermore’s concerns with the time deadlines for NIF amplifier glass production, LLNL authorized Schott and Hoya to proceed with building of the full scale factories.

Last fiscal year the first batches of full-sized NIF amplifier glass were delivered and found to be below specifications for a number of reasons: platinum inclusions, volume inhomogeneities, surface ripples and water content. Importantly, the full scale glass factories as well as the prototypes have not produced laser amplifier glass meeting NIF specifications. Schott and Hoya have now reassured LLNL that they understand the problems, and they will be fixed soon. Nevertheless, Livermore can not state at this time that the NIF amplifier glass can be delivered either on time or on budget. There are serious doubts about whether or not continuous-melting will in the end be a viable approach for fabricating these crucial NIF components. If Livermore is forced to return to the older glass pouring techniques used for the Nova laser, the time delays and cost increases in the NIF will be far greater than anything yet considered.

2) Anti-Reflective Optical Coatings: Much has been achieved in the raising the damage threshold of optical coatings at Livermore. Nevertheless, the NIF is pushing the technology and new difficulties can and did arise. Anti-reflective optical coatings are necessary to prevent laser energy losses and to protect the optics components from high-fluence damage. Currently problems persist with the anti-reflective coating on the frequency-tripling potassium dihydrogen phosphate (KDP) crystals and with the anti-reflective coating on the diffraction grating which steers the 1w- and 2w-light out of the target chamber. These are crucial issues for the performance of the NIF, and it could mean that each of the NIF beam lines will only be able to produce a small fraction of their design energy at 3w.

3) Spatial Filters: Livermore has calculated that ignition can only be achieved at the NIF using a long pulse: 20 nsec in total with about a 3 nsec high intensity component. In order to accommodate such a long pulse, the NIF spatial filters must stay open for about 20 nsec. LLNL claims to have devised a means to keep NIF’s spatial filters open for the required 20 nsec, but this solution was never fully tested on the prototype Beamlet laser.

4) Ignition Target Fabrication: The original LLNL ignition target "point design" had a plastic ablator surrounding the fusion fuel. This design required significant research and development in the area of cryogenics. Around 1996-1997 the plastic ablator design was abandoned because further calculations at LLNL showed that -- for realistic targets -- the plastic would mix with the fusion fuel as the target imploded to such an extent that the mixing would prevent ignition. When this was realized, Livermore managers diverted funds and manpower out of the cryogenic target program. It appears that the programmatic shift away from cryogenic plastic targets was never aligned with overall project management and cost accounting, however, nor fully explained to the cognizant oversight committees in Congress.

The next idea for an ignition target, widely discussed at the 1997 American Physical Society’s Division of Plasma Physics Annual Meeting in Pittsburgh, PA, was to use beryllium as the ablator material. Beryllium ignition targets have the advantages over plastic targets that: 1) the ablation rate is higher, reducing the rate of mixing with fusion fuel during implosion; and 2) the material strength of beryllium is such that the required amount of deuterium-tritium gas can be held at room temperature. Beryllium target fabrication research is largely conducted at Los Alamos National Laboratory. It now appears that beryllium cannot be used as an ablator due to the fact that welding the two beryllium hemispheres together produces a weld line which interferes with the strict requirements for spherical symmetry in the target capsule.

The situation facing the National Ignition Facility today is that, after more than half a billion dollars appropriated, there are no ignition targets. Simply put, the ignition target capsule designs which LLNL claims "ignite" in computer simulations cannot be fabricated.

A project like the NIF pushes the forefront of technology along many lines. New technologies going into NIF should have been tested as thoroughly as possible prior to the construction of NIF. In Livermore’s "Beamlet" laser, the prototype for the NIF, there existed the opportunity to do a full systems test of the modular NIF design concept. Unfortunately no Beamlet shot ever simultaneously tested the full set of NIF performance goals: a full energy, full pulse length shot converted to third harmonic and focused onto a target.

In sum, serious problems exist with the NIF project that merit close scrutiny -- problems well beyond the clean room issue. There is now no evidence that NIF can attain the key laser energy, power, pulse shape, shot rate, wavelength or other key design parameters, or that a capsule believed capable of ignition can be fabricated. These problems are in fact so severe that there is no technical, engineering or scientific basis for having confidence that NIF can achieve its advertised objective of fusion ignition in the laboratory. Nor is there any confidence at this time that NIF can serve as a facility where useful experiments in the region of temperature, pressure and energy density characteristic of nuclear explosions can be performed. The Task Force should use the full breadth of their mandate to comprehensively assess the NIF project. It is obvious that two weeks is insufficient time to produce a report that adequately addresses the issues noted above.

Sincerely,