The article by Jim Dawson on the NIF controversy (Physics Today, January 2001, page 21) quotes Burton Richter as saying that it would take Lawrence Livermore National Laboratory (LLNL) two or three years to bring the National Ignition Facility (NIF) laser up to full performance, and that this was typical of projects of this kind. That viewpoint is not supported by the story of LLNL's previous laser, called Nova. In their 1980 laser program annual report,1 LLNL researchers calculated an expected performance for Nova of 9-10 kJ/beam at the third harmonic. In their 1981 annual report (p. 2-28), at the start of Nova construction, they proposed operating criteria of 4-7 kJ/beam. The 1981 report also stated that the "primary programmatic objective for Nova," using an eventual 20 beam lines, would be "demonstrating the ignition of thermonuclear burn." The Nova laser worked poorly when it was completed. After several years of fixes and upgrades, the useful energy for laser-target hohlraum experiments at the third harmonic reached 3 kJ/beam. The ignition goal for Nova was discarded.
Ed Moses is quoted as saying that there has been no loosening in any way of the criteria for project completion of NIF. LLNL specifications for NIF had been 9.4 kJ/beam in a shaped 20-nanosecond pulse, with 98% of the energy focused to within a 600-micron spot size, with optical beam smoothing. LLNL scientists calculated that about 9 kJ/beam is needed to drive their target design to ignition; 20-ns-long pulse shapes are needed to create ignition conditions; the 600-µm focal-spot size is needed to fit the laser light through the entrance holes of their hohlraum target; and the optical beam smoothing is needed to control laser-plasma instabilities. This time, to reach ignition, there would be 192 beams. NIF would also use a different laser design than Nova.
The Department of Energy submitted draft NIF milestone definitions to Congress on 15 September 2000, and then to a NIF review panel on 16 November 2000. These milestones call for acceptance of the first eight beams in December 2004 with 5 kJ/beam of third-harmonic light in an unshaped 5-ns pulse.
The full 192-beam system would be accepted in September 2008 with
5.2 kJ/beam in an unshaped 5-ns pulse. The draft includes no specifications on focusing or beam smoothing. This watering down of the NIF milestones is important because the scientific prototype of NIF, called Beamlet, was never operated simultaneously at full energy, full pulse duration, conversion to third harmonic, with focusing.
Sidney Drell is quoted as saying that he supports NIF, independent of whether it achieves ignition, as a way of attracting bright young scientists to LLNL. Actually, over the past year, the LLNL laser fusion program has lost some of its best laser and target scientists. But if we assume that NIF is eventually completed, at some performance level, then we need to ask a fundamental question: What kind of scientist is needed to maintain an existing set of nuclear weapons, as compared to designing or improving these weapons? Maintenance requires different skills and attitudes than design. Is an entrepreneurial and risky undertaking like the laser fusion program2 the appropriate vehicle to attract these scientists? Will laser fusion scientists be sufficiently cautious about making changes in the weapons stockpile, or will they be risk-takers? Will they make unnecessary changes in the nuclear weapons to justify, to themselves and to their sponsors, the high capital and operating costs of NIF?
References
1. Lawrence Livermore National Laboratory, Laser Program Annual Reports, rep. no. UCRL-50021-80 LLNL, Livermore, Calif. (1980; see Figure 2-114) and rep. no. UCRL-50021-81 (1981); available from the National Technical Information Service.
Edward Moses replies: We must respectfully disagree with the opinions of Stephen Bodner. His views of the National Ignition Facility, Nova, and the US nuclear weapons Stockpile Stewardship Program are well known. During the many reviews that preceded the authorization of the NIF Project, Bodner expressed his concerns to the committees. These committees, and those that succeeded them, have continued to support NIF.
Bodner's representation of Nova neglects to mention that, in addition to meeting its 30-terawatt performance goal, it completed 14 000 shots over its 14 years of operation. Nova was the world's premier high-energy density physics experimental facility, where the highest quality data in hydrodynamics, plasma physics, materials science, and inertial confinement fusion were generated and the first x-ray laser was demonstrated. Over 1000 journal articles were produced and a generation of laser and laser-plasma physicists was trained.
Bodner states that NIF's specifications have been "watered down" and the NIF prototype laser, Beamlet, never met its performance requirements. In fact, Beamlet demonstrated full energy, full power, temporally shaped ultraviolet laser pulses. All aspects of Beamlet design and operation were reported in 31 journal articles. Our Beamlet experience gives us high confidence that NIF will meet its full performance goals.
Bodner raises the question of whether NIF scientists will show good judgment as future stewards of the nation's nuclear stockpile. History speaks for itself. During the past 25 years, the very same people who developed and used similar facilities are now an integral part of the nation's Stockpile Stewardship Program, committed to maintaining its safety and reliability without weapons testing. State-of-the-art facilities like NIF are needed to draw and challenge the best-qualified scientists. NIF will play a vital role in our national security while pushing the boundaries of experimental and theoretical science.
Numerous reviews conducted by the NAS, DOE, and the University of California uniformly support the view that NIF can meet its technical and scientific goals. The NIF team is working to ensure this will happen.
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