Fusion hopeful hits temperature high.

An extraordinary X-ray machine considered the comeback kid of fusion-energy research has burned past the 2-million-degree temperature mark. Above that hellish threshold, nuclear fusion of hydrogen atoms becomes possible.

The machine at Sandia National Laboratories in Albuquerque, N.M., known simply as "Z" (SN: 1/17/98, p. 46), propels a huge electric charge into a hollow cylindrical array of thin wires. The current vaporizes the strands into a plasma, an intensely hot gas of atoms shorn of electrons. It also creates magnetic fields that crush the plasma, unleashing X rays.

With the milestone now exceeded--the plasma has reached 2.3 million [degrees] C--research on so-called pulsed-power fusion enters a new era, says Donald L. Cook, Sandia's pulsed-power program leader. Already, scientists have made four tests of Z's ability to squeeze capsules of hydrogen fuel placed inside the wire cages. The intense X rays can compress fuel pellets to enormous densities, approaching the requirements for fusion. After 30 years of pulsed-power development, Cook says, "we've crossed the threshold to where we can do capsule experiments" that were formerly possible only in laser fusion chambers (SN: 10/19/96, p. 254).

Although Z already exceeds lasers in power and energy and is now invading their temperature range, pulsed power has a long way to go to surpass lasers as a step toward self-sustaining fusion, Cook says. For instance, Z crushes capsules into minuscule cigars rather than keeping them spherical, a shape needed to ignite a thermonuclear reaction. Sandia announced Z's temperature achievement on Dec. 17.