Thor's hammer to crush materials at 1 million atmospheres
by Staff Writers
Albuquerque NM (SPX) Jan 07, 2016
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
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, eliminating 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
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."
Another advantage for Thor in such testing is that each capacitor's transit time can be not only controlled to the nanosecond level but isolated from the other capacitors. "In 30 seconds on a computer, we can determine the shape of the pulse that will produce a desired compression curve, whereas it takes days to determine how to create the ideal pulse shape for a Z experiment," Reisman said.
Furthermore, because Thor can fire so frequently - less hardware damage per shot requires fewer technicians and enables more rapid rebooting - researchers will have many more opportunities to test an idea, he said.
But there's more at stake than extra experiments or even new diagnostics. There's testing the efficiency of a radically different accelerator design.
Everything depends upon adding bricks. Sandia is building Thor in stages and already has assembled materials. Two intermediate stages are expected in 2016. These will comprise 24 bricks (Thor 24) and 48 bricks (Thor 48). "These are 'first-light' machines that will be used for initial experiments and validation," Reisman said. Thor 144, when completed, should reach 1 million atmospheres of pressure.
Sandia manager Bill Stygar said more powerful LTD versions of Z ultimately could bring about thermonuclear ignition and even high-yield fusion. Ignition would be achieved when the fusion target driven by the machine releases more energy in fusion than the electrical energy delivered by the machine to the target. High yield would be achieved when the fusion energy released exceeds the energy initially stored by the machine's capacitors.
The academic community also is interested in Thor's architecture. "Part of the motivation for Thor was to develop affordable and compact machines that could be operated at universities," said Reisman. Institutions that have expressed interest include Cornell University, University of California San Diego, Imperial College London and the Carnegie Institution.
Thor's theoretical design was supported by Sandia's Laboratory Directed Research and Development office; later engineering details and hardware were supported by the National Nuclear Security Administration's Science Campaign.
Sandia National Laboratories
Space Technology News - Applications and Research
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