microphysics data, enable integrated code validation, and create hohlraum conditions unique in a laboratory setting (high radiation temperatures foremost among them).

One of the stated goals of the SBSS program is to maintain core intellectual and technical competencies in nuclear weapons in the absence of nuclear testing. This key aim of SBSS requires a challenging theoretical, computational, and experimental program in the areas of implosion hydrodynamics, instabilities and mix, radiation transport, and theormonuclear burn. In the committee's judgment, ICF provides a unique synthesis of these relevant physics areas, and the NIF would provide unique capabilities for basic experiments in atomic physics, radiation flows, plasma physics, and hydrodynamics. In the collective judgment of the committee, the NIF should stimulate the scientific imagination and attract excellent scientists and engineers more than any other proposed element of SBSS. This assertion is supported by the ICF program's history of attracting and retaining high-quality personnel. Indeed, the attraction of the NIF is so high that it may be a management and leadership challenge to keep the ICF program in proper balance with the rest of SBSS.

Prior to the start of the moratorium on nuclear testing, weapons designers could unambiguously confirm their judgments and refine their skills through the success or failure of their devices in underground tests. In the new era of a complete nuclear test ban, the NIF can provide weapons stewards with a similarly challenging alternative for refining and proving their skills. Predicting ICF results in well-diagnosed experiments and ultimately achieving ignition are in many respects more technically demanding than making a nuclear weapon work.

The NIF will provide unique experimental conditions in a controlled environment from which extensive and relevant data can be extracted for both ICF and SBSS applications. The decision to undertake a policy of SBSS implies moving in the direction of first-principles predictive capability in hydrodynamics and radiation transport. While other facilities are expected to provide similar data, the NIF will access different regimes of such parameters as temperature, density, and scale length. Current and former members of the weapons community are debating the extent to which the data to be gained on facilities such as the NIF are applicable to the stockpile. As SBSS is a venture into uncharted technical and organizational territory, this issue can only be resolved by experience. Although many real engineering issues would not be tested directly on facilities such as the NIF, a skilled practitioner could use NIF experiments to develop an understanding of the relevant physics and apply the judgment he develops to analyze stockpile problems as they arise.

SCIENTIFIC READINESS

The NOVA Technical Contract (NTC) of 19903 specifies seven experimental objectives in hohlraum laser physics (HLP 1 to 7) and five in hydrodynamic equivalent physics (HEP 1 to 5) that were to be completed in preparation for proceeding to construction of an ignition facility. Although the completion of the NTC cannot guarantee that ignition will be achieved with the NIF, the completion of each milestone, in the context of the understanding of the underlying physics gained in pursuing it, increases confidence in the extrapolation of the results to the performance of the NIF. DOE's assessment of the technical readiness to proceed to Critical Decision 2 (CD-2)4 was based partly on sustained progress on the NTC and on the extrapolation of those results to the NIF. Since CD-2, the NIF baseline target design has been changed to a gas-filled hohlraum. This change introduced unexpected but seemingly reproducible beam bending and increased backscatter so that several of the HLP 1 to 6 milestones are no longer met and others are, at best, barely met. The cause of this unexpected behavior is thought to be understood, and experiments with one NOVA beam smoothed indicate that beam

3  

National Research Council, Review of the Department of Energy's Inertial Confinement Fusion Program: Final Report, National Academy Press, Washington, D.C., September 1990. The NTC requirements are summarized in Table 1.

4  

Steps taken by the DOE toward construction and operation of the NIF are called Critical Decisions (formerly Key Decisions). Critical Decisions 1 and 2 (approval of mission need, and project approval) have already occurred. The remaining Critical Decisions are CD-3 (authorization for start of physical construction and procurement, scheduled for April 1997) and CD-4 (end of construction project, scheduled for September 2003).



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