More Crushes on Thor


The silver disk that is the new machine’s central power flow assembly. Image: Randy Montoya / Sandia National Laboratories

The famed “Z machine” at Sandia National Laboratories is a massive, monstrous beast, capable of crushing material with 100-nanosecond-long bursts five million atmospheres strong. But to do that, the accelerator requires 10,000 square feet of space and a significant amount of maintenance between bursts. Any scientist hoping to give a dollop of deuterium a good squeeze only gets the chance a few times a year.

To remedy the situation, Sandia is building Thor. Where the Z machine uses massive capacitors that need massive switches to trim a pulse down to a 100-nanoseconds, this new, smaller accelerator will use new smaller capacitors called bricks. They don’t need the giant switches to shorten the pulse and they require much less upkeep. The bricks will allow the facility to be a fifth the size of the Z machine and some 40 times more efficient. “Scientists are getting two or three tests a year on the Z machine,” says David Reisman, the lead engineer and project manager for the new accelerator. “I could get 10 shots a week on Thor.” The higher volume of shots would mean, of course, much larger data sets, and the development of diagnostics.

The bricks also allow Thor’s pulse to be fine-tuned to avoid shock waves that would otherwise alter whatever material was being examined. “We can change the ordering to shape things in the way that we want, like a piano. We have individual notes that we can use to get what we want,” says Reisman. “So we can study the material in the unmelted solid form, where it still has atomic structure and strength and things like that.” The ability to “play” the pulse shape will also allow researchers to examine how materials cross phase boundaries and go form one crystal structure to another.

Installing a gas exhaust line for a switch at Thor’s brick tower racks. Image: Randy Montoya / Sandia National Laboratories

Major advances in capacitor and switching technology have given rise to the bricks. Highly reliable and efficient, it’s their size that determines the size of the pulse. So each brick has less current: 50,000 amps. They’re added together to get the desired current. “So that’s the tradeoff,” says Reisman. “You don’t have these big pulse forming lines and these big machines but then you have a lot of these guys you have to trigger separately.”

The smaller size means Thor’s crushing power is limited to a mere million atmospheres. But that’s enough for most of the researchers hoping to put pulsed power to use. The Z machine’s powerful “Z pinch” was initially conceived of as a tool for researching fusion. Recently, though, the majority of tests run on it have been isotropic compression experiments, which don’t need all five million atmospheres. If those researchers could do their work on a smaller machine, it would free up the Z machine for fusion-specific work.

Already universities are clamoring to get their hands on Thor or its offspring. But they’ll have to wait until Sandia has proved its feasibility. “We’re going to validate things here and then pursue that,” says Reisman. Once the junior accelerator has proliferated to some degree, researchers are likely to achieve a better understanding of what’s in the center of our world as well as worlds more distant. “People want to study materials that are important to geophysics and to planetary physics, where there’s a lot of uncertainty in those material properties,” says Reisman. “This is important because they are discovering thousands of these planets outside our solar system, and to really understand the formation of the planets and their composition, they need to have accurate material data under high pressure.

“My hope for this machine is that it will help that effort.”

Michael Abrams is an independent writer.

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Scientists are getting two or three tests a year on the Z machine. I could get 10 shots a week on Thor.

David Reisman, Sandia National Laboratories


June 2016

by Michael Abrams,