The Dual-Axis Radiographic Hydrodynamic Testing facility would be used by the DOE to study the behavior of warhead primaries during detonation. "Dual-Axis" refers to two very large X-ray machines which are used to take "radiographs" (X-ray photographs) of the implosion of a mock-up nuclear warhead pit. The materials tested can be depleted uranium or plutonium-242, a non-fissile isotope of plutonium. As discussed above, "hydrodynamic" refers to the fact that under the extreme pressure and temperature conditions of implosion, these materials take on the qualities of liquids, and therefore their physical behavior can be modeled by equations which apply to liquids. Like all hydrodynamic facilities, DARHT can be used for new weapons design.

According to its proponents, the two main improvements of DARHT over other hydrodynamic testing facilities (see table of other facilities) are the increased resolution of radiographic images, and the use of two axes instead of one. The second axis allows for three-dimensional observation of the compressed materials simulating the pit of a warhead. However, Seymour Sack, a Laboratory Associate at Livermore, argues that the information that DARHT is designed to provide can be gleaned through small-scale experiments at existing or upgraded facilities.

The DOE plans to use the information gained from hydrodynamic and dynamic experiments to validate or refine the computer codes used to model warheads. According to the DOE, the computer models would be used to predict possible problems with primaries, or as one test of whether a corrective action would work. (However, new codes based on data from SBSS facilities will be less accurate when applied to existing warheads and could adversely affect safety and reliability.) Hydrodynamic testing could also be used to certify certain weapons components after re-manufacture or design. The total estimated cost of the new DARHT facility is $123.8 million.

Go to table to hydrodynamic testing facilities and high energy density testing facilities and accelerators

The National Ignition Facility (NIF)

Considered one of the cornerstones of the SBSS program, the National Ignition Facility would use lasers to produce X-rays to study fusion at low volumes. The process involves Inertial Confinement Fusion experiments in which powerful lasers are used to superheat a minute capsule of deuterium and tritium to the point of ignition, resulting in a self-sustaining thermonuclear burn -- a tiny thermonuclear explosion.

Since NIF is expected to be able to operate at energy densities similar to the level of a nuclear explosion, it can be used to study the thermonuclear phenomena that occur in nuclear warheads during detonation. This would allow weapons designers to gain information on new weapons design concepts without nuclear weapons testing, though it would not contribute significantly to understanding the types of problems that have historically affected the secondaries of warheads.

Even at the high densities possible through NIF, the total energy released in the experiments is from 10,000 to a billion times less than that of a nuclear weapons test and must be appropriately scaled to be useful in accurately assessing the operation of existing warheads. NIF can only examine isolated fusion phenomena and is incapable of exactly simulating the complex interplay of a variety of fission, fusion, and non-nuclear physical processes that occur in a nuclear explosion. It would therefore be irrelevant to studying or assuring the nuclear safety of existing warheads, but would enable advances in the design of new ones. Proponents claim that NIF would be relevant to studying reliability. However, IEER has tentatively concluded that DOE's definition of reliability seems to relate mainly to first strike capability rather than maintaining retaliatory deterrence. The National Ignition Facility is estimated to cost about $1 billion.

Go to table to hydrodynamic testing facilities and high energy density testing facilities and accelerators