Sandia National LaboratoriesAlbuquerque, N. Mex.

Z Accelerator for fusion and materials research

Doug Bartholomew, Samuel Greengard, Glenn Hasek, John Jesitus, Scott Leibs, Kristin Ohlson, Robert Patton, Barb Schmitz, Tim Stevens, and John Teresko contributed to this article. This summer, while a British team was setting a new land-speed record for automobiles in the Utah desert, a team of researchers a few hundred miles to the southeast -- at Sandia Labs -- was doing some acceleration work of its own. The results may have a profound impact on everything from nuclear weapons to microlithography to astronomy to perhaps achieving the dream of tapping fusion reactions for a limitless source of energy. The physicists, engineers, and others are doing their work with a device called the Z accelerator, a device that produces an X-ray environment that enables the study of fusion in the laboratory. A combination of the very big and the very small, the Z accelerator is more than 100 ft in diameter and almost 20 feet tall. But at its heart is an array of 100 to 400 wires, each about one-tenth the thickness of a human hair, housed in a spool-like device called a hohlraum that measures about 15 mm by 30 mm. When these wires are vaporized (by 36 pulsed-power devices), the resulting plasma is "pinched" into densities and temperatures high enough to produce X-rays. (The Z accelerator facilitates the study of fusion phenomena by generating an X-ray environment that is 1,000 times larger than that produced by lasers and which lasts longer.) The X-rays are confined in the thimble-sized hohlraum, which radiates at a temperature above 1.2 million C. Its immediate application at Sandia is in studying nuclear-weapons performance now that underground tests are banned. Finding a way to continue this work in a laboratory setting has become critical, and physicists at Los Alamos National Laboratory have requested a minimum of two experiments per month on an ongoing basis. But Z's usefulness doesn't stop there. The Sandia project has already spawned one spinoff company -- Quantum Manufacturing Technologies Inc. Using a smaller and less energetic version of the same pulsed-power technology that is at the heart of Z, it treats metal, ceramic, and plastic surfaces, making them harder, tougher, and more resistant to corrosion and fatigue. And if these fusion experiments are carried to their logical extreme, the entire energy industry -- all industries, for that matter -- would be transformed, thanks to an endlessly renewable source of power. The efforts to tap fusion as an inexhaustible source of energy "was the application that initially prompted work on what has become Z," says Keith Matzen, high-energy density physics program manager. Another application, according to Art Toor, a scientist at Lawrence Livermore National Laboratory in Livermore, Calif., is the study of "astrophysical opacities" that may, for example, help to explain the behavior of supernovas and related phenomena. The device has already led to the first plausible explanations of certain pulsations emanating from stars, by allowing for iron to be heated to the point at which its opacity can be measured. This "Z-pinch" method of producing X-rays has been around since the 1950s, but only in the last couple of years have huge leaps in performance become possible, by combining the most recent generation of accelerators with new methods of mounting more and thinner wires into an array. "The value of the Z accelerator is that it can drive experiments that last longer," Livermore's Toor says, "making it possible to examine entire new areas that just aren't possible using other energy sources." What's ahead for Z and its successors? Sandia physicists say that at some point, X-rays from a Z-pinch experiment will implode a BB-sized capsule of fusion fuel placed inside a hohlraum, thus bringing us close to, or even reaching, the point at which fusion can produce more energy than is required to initiate it. And that may mean that the "ultimate energy source" will be upon us.

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