Sandia National Laboratories technician Eric Breden installs a transmission cable on the silver disk that is the new pulsed-power machine’s central powerflow assembly. Credit: Randy Montoya
A new Sandia National Laboratories accelerator called Thor is expected to be 40X 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.
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. 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. 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.”
Sandia National Laboratories technician Tommy Mulville installs a gas exhaust line for a switch at Thor’s brick tower racks. In the background, beyond the intermediate support towers, technician Eric Breden makes ready an electrical cable for insertion in the central power flow assembly. Credit: Randy Montoya
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. Also, as Thor can fire so frequently—less hardware damage per shot requires fewer technicians and enables more rapid rebooting— so more opportunities to test an idea.
Thor’s shoebox-sized units, known as “bricks,” contain 2 capacitors and a switch. Everything depends upon adding bricks. Sandia is building Thor in stages and already has assembled materials. 2 intermediate stages are expected in 2016. These have 24 bricks (Thor 24) and 48 bricks (Thor 48). Thor 144, when completed, should reach 1 million atmospheres of pressure.
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.
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