Thor's Hammer to Crush Materials at 1 Million Atmospheres

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A new Sandia National Laboratories accelerator called Thor is expected to be 40 times more efficient than Sandia’s Z machine, the world’s largest and most powerful pulsed-power accelerator, in generating pressures to study materials under extreme conditions.

“Thor’s magnetic field will reach about one million atmospheres, about the pressures at Earth’s core,” said David Reisman,  lead theoretical physicist of the project.

Though unable to match Z’s 5 million atmospheres, the completed Thor will be smaller — 2,000 rather than 10,000 square feet — and will be considerably more efficient due to design improvements that use hundreds of small capacitors instead of Z’s few large ones.

Remarkable structural transformation

This change resembles the transformation of computer architecture in which a single extremely powerful computer chip was replaced with many relatively simple chips working in unison, or to the evolution from several high-voltage vacuum tubes to computers powered by a much larger number of low-voltage solid-state switches.

A major benefit in efficiency is that while Z’s elephant-sized capacitors require large switches to shorten the machine’s electrical pulse from a microsecond to 100 nanoseconds, with its attendant greater impact, the small switches that service Thor’s capacitors discharge current in a 100-nanosecond pulse immediately, obviating energy losses inevitable when compressing a long pulse.

The new architecture also allows finer control of the pulse sent to probe materials.

Toward a more perfect pulse shape

Said Reisman, “Individual cables from pairs of capacitors separate our signals. By combining these signals in any manner we choose, we can tailor very precise pulses of electrical current.”

Tailored pulse shapes are needed to avoid shocks that would force materials being investigated to change state. “We want the material to stay in its solid state as we pass it through increasing pressures,” he said. “If we shock the material, it becomes a hot liquid and doesn’t give us information.”

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