DRAMATIC changes in U.S. nuclear weapons policy have followed the end of the Cold War, among them halts to the development of new types of weapons and to weapon testing. The current stockpile must remain safe, secure, and reliable into the indefinite future as it undergoes changes caused by aging or remanufacturing and replacement of aging components. This challenge has led to the development by DOE of the Stockpile Stewardship and Management Program. Henceforth, confidence in America's nuclear arsenal will depend more than ever on our fundamental understanding of weapon science and technology. That understanding must now be pursued without recourse to system-level tests of integrated performance-the detonation of full-scale nuclear devices.
Scientists have turned to several tools, including advanced hydrotesting, subcritical experiments, advanced computer simulation and modeling, and what have come to be called superlasers, to address some of the remaining scientific issues. Nuclear detonations produce enormous total energy; no laboratory tool can deliver more than a small fraction of nuclear yield. But nuclear detonations also produce very high levels of energy per unit volume, that is, high energy density. High-power lasers can approach such high energy densities, even if only momentarily in very small spaces. Extremely powerful lasers can, in short, create microscopic versions of some important aspects of nuclear detonations, something available through no other experimental technique. They also can permit the production and study of fusion ignition in the laboratory.
As a result of superlasers and other laboratory tools, the study of high-energy-density physics can be moved from the Nevada Test Site to the laboratory, at least in part. Doing so can offer some real advantages. High-power lasers can support more frequent experiments than full-scale weapon testing could. They also offer more precise control of experimental conditions and greater access for detailed measurements; that is, the variables can, to some extent, be separated. These capabilities contribute significantly to the feasibility of stockpile stewardship and management.
The development of high-power lasers has enhanced the ability to pursue basic research on nuclear detonation. Since 1985, weapon scientists from various laboratories have used the Nova laser system to conduct more than 12,000 experiments. Even as Nova research continues, preparations are under way for its successor; the National Ignition Facility will become a cornerstone of DOE's Stockpile Stewardship and Management Program.
Although ten times more powerful and forty times more energetic than Nova, NIF will still produce total energies only a tiny fraction of those in full-scale nuclear detonations-total energy in the laser beams will be equivalent to a half pound of TNT, or one billionth of the energy of a nuclear weapon. Yet NIF will be able to approach much more closely than Nova the range of high energy-densities (and therefore temperatures) produced by nuclear weapons and necessary to achieve fusion ignition. With NIF, many of the fundamental processes of thermonuclear detonation become, for the first time, fully accessible to laboratory study and analysis. As a bonus, NIF will provide a unique means of testing nuclear weapon effects and a powerful new tool for basic science applications of high-energy-density physics (e.g., astrophysics, plasma physics, and fusion energy).
The next generation of superlasers, such as NIF in the United States and the French Laser MegaJoule (LMJ), will provide still more detailed understanding of the processes of nuclear detonation. It will enable scientists to gain a much improved understanding of the basic physics of nuclear weapons, greatly enhance their ability to predict weapon performance, and provide a sounder basis for assuring the safety and reliability of the nuclear stockpile.

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