Published September 23, 2012
A crushed tube the size of a thread spool has brought the United States one step closer to harnessing nuclear fusion as a clean, almost limitless power source.
The experiment at Sandia National Laboratories in New Mexico tested how well a tiny cylinder could withstand the crushing magnetic force from the lab's "Z machine" — a pulsed-power accelerator that zapped the cylinder with 25 million amperes of electric current. The "liner" cylinder collapsed on itself, as would be expected, but remained intact enough to theoretically squeeze together deuterium or tritium fuel, triggering nuclear fusion.
"Our experiments were designed to test a sweet spot predicted by the simulations where a sufficiently robust liner could implode with a sufficiently high velocity," said Ryan McBride, a researcher at the laboratories in Albuquerque.
Such careful balance is needed to crush the beryllium cylinder in the right way to achieve sustainable fusion someday. A thicker cylinder would make the crushing implosion less efficient, and a thinner cylinder could rip apart under the stress.
The cylinder is designed to hold a BB-sized fuel capsule containing deuterium fuel. Seawater contains huge amounts of deuterium, an isotope of hydrogen, and half a bathtub of seawater could theoretically create the energy equivalent of 40 train cars of coal.
Both the cylinder and its tiny fuel capsule represent the possibility for achieving inertial confinement fusion — the cylinder's implosion would compress the deuterium fuel and heat it to temperatures similar to those in the core of the sun. Such fusion processes power stars.
The Sandia test used a laser to preheat the metal cylinder before zapping it with electricity to create the crushing magnetic fields. Other inertial confinement fusion efforts would harness even more powerful lasers, such as the cluster of lasers at the National Ignition Facility that focus like a mini-Death Star on a target. [Record-Breaking Laser Shot Paves Way to Fusion Energy]
Sandia researchers have used simulations to show that their Z machine could trigger "break-even" nuclear fusion that creates just a bit more energy than it takes in. But a more powerful machine could eventually lead to "high-gain" fusion using the new crushing technique, creating more than 1,000 times the energy put in, thereby making fusion power practical.
The next steps in the march toward fusion involve testing the laser preheating and secondary magnetic fields that would keep charged particles from escaping the hot fuel — tests scheduled for December. Researchers hope to test the entire concept before the end of next year.
"We are now confident enough to take the next steps on the Z facility of integrating in the new magnetic field and laser preheat capabilities that will be required to test the full concept," said Dan Sinars, manager at Sandia National Laboratories.
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