A Dry Run For Fusion Power
The reality of fusion
power the same energy that powers the sun remains outside of our reach. Although scientists have figured out how to split atoms and attain nuclear reactions, they have yet to find an efficient way to fuse atoms. So far, techniques require more energy than what's produced.
But at Sandia labs, researchers are getting closer. Recent experiments led by plasma physicist Ryan McBride show that it's possible to reach a
"break even" point, where the energy that goes into running a fusion
reactor is equal to energy produced. That's a big step toward an alternative energy that produces emission-free energy without the nuclear waste.
The fusion method at Sandia is called
magnetized inertial fusion. Doing it requires a system of coils at each end of a beryllium cylinder just under seven millimeters across. Inside the cylinder is a small amount
of deuterium, which is an abundant molecule in the ocean made of hydrogen with an extra neutron.
Here's how the reactor works: First the two coils generate a magnetic field. A few milliseconds later, an accelerator called the Z machine fires a 25-million-ampere current. That current generates a magnetic field that crushes the cylinder in 100 billionths of a second. In that short space of time a laser fires at the cylinder, heating the deuterium gas inside and turning it into a plasma. The two coils at the end, meanwhile, are generating a magnetic field that contains the plasma to allow it to fuse.
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In this experiment, the compression part of that system was tested. The current was run through the coils and the beryllium cylinder was compressed, and retained its shape. This is important because if the cylinder deforms too much, there isn't enough pressure on the whole sample deuterium to initiate fusion.
One of the factors that
Sandia labs was trying to determine was how thick and large the cylinder should
be. Too big, and the magnetic fields can't crush it. Too small and the
electrical current will simply vaporize it completely before it can crush the
plasma inside. They found the optimum proportion seems to be a cylinder with a wall about one sixth the radius.
The experiment is an
extension of simulations performed
in March. The next step is to try pre-heating the deuterium with the laser, and after that — possibly some time in late 2013 — testing it with nuclear fuel inside. The fuel will be deuterium, and it won't be powerful enough to get past the "break even" point and produce energy. But McBride told Discovery News that the output should tell the researhers whether or not using tritium — hydrogen with two neutrons — will work when mixed with deuterium.
So will this lead directly
to fusion reactors? Not really, because the amount of current needed to get to
"high gain" fusion — which would mean energy output more than 1,000 times that applied to the fuel — is more than twice what the Z machine can produce, some 60 million amperes. That said, if the
proof-of-concept works, then there isn't any technical barrier to building such
The experiment will be presented in an upcoming issue of Physical Review Letters.
Top Photo: Sandia researcher Ryan McBride pays close attention to the tiny central beryllium liner to be imploded by the powerful magnetic field generated by Sandia’s Z machine. The larger cylinders forming a circle on the exterior of the base plate measure Z’s load current by picking up the generated magnetic field.
Image: Sandia National Laboratories