Nuclear fusion might be achieved in a preheated cylindrical container immersed in strong magnetic fields. A series of computer simulations performed at Sandia National Laboratories show the release of output energy that was, remarkably, many times greater than the energy fed into the simulation.
Sandia researcher Steve Slutz, lead author of the paper published at Physical Review Letters said, “People didn’t think there was a high-gain option for magnetized inertial fusion (MIF) but these numerical simulations show there is. Now we have to see if nature will let us do it. In principle, we don’t know why we can’t.” Take that to mean “might” moves to “could”.
The Sandia team is talking about high-gain or quite substantial returns past breakeven reactions.
Before we get too far lets have a very brief refresher. The two leading Inertial Electrostatic Confinement (ICE) paths are from Dr. Robert Bussard with quite a bit of design information and the Rostocker design handled quietly by Tri-Alpha Energy. Add to those the plasma method gaining ground designed and led by Eric Lerner. The easiest comparison is the Bussard confinement design – a semi spherical (essentially a cube) volume held by magnetic fields within which fusion is occurring and expected to get past breakeven.
Where Sandia Lab team diverges is the semi sphere is instead a cylinder.
Two years ago the Sandia team proposed the cylinder idea with simulations that offered, “significant fusion yields may be obtained by pulsed-power-driven implosions of cylindrical metal liners onto magnetized (>T) 10 and preheated (100–500 eV) deuterium-tritium (DT) fuel.” What was learned was key, the cylinder idea builds a confinement strong enough to hold in the heat and keep the alpha particles inside – that keeps the energy loss way down. More simulations and tests were planned . . .
This year the press release explains the MIF technique heats the fusion fuel (deuterium-tritium) by compression as in normal inertial fusion, but uses a magnetic field to suppress heat loss during implosion. The magnetic field surrounds a small liner so together they act like a kind of shower curtain to prevent charged particles like electrons and alpha particles from leaving the party early and draining energy from the reaction.
At the top and bottom of the liner are two slightly larger coils that, when electrically powered, create a joined vertical magnetic field that penetrates into the liner, reducing energy loss from charged particles attempting to escape through the liner’s walls.
Once set up the simulated process relies upon a single, relatively low-powered laser to preheat a deuterium-tritium gas mixture that sits within the liner.
An extremely strong magnetic field is created on the surface of the liner by a separate, very powerful electrical current, generated by a pulsed power accelerator such as the Sandia Z accelerator machine. The force of this huge magnetic field pushes the liner inward to a fraction of its original diameter. It also compresses the magnetic field emanating from the coils. The combination is powerful enough to force atoms of gaseous fuel into intimate contact with each other, fusing them.
What they get is an implosion, everything crashing in rather than exploding out. The product we’re interested in is heat, and the new work shows there is a lot of it.
Heat released from that reaction raises the gaseous fuel’s temperature high enough to ignite a layer of frozen and therefore denser deuterium-tritium fuel coating the inside of the liner. The heat transfer is similar to the way kindling heats a log: when the log ignites, the real heat – here high-yield fusion from ignited frozen fuel – begins.
Tests of physical equipment necessary to validate the computer simulations are already under way at Sandia’s Z accelerator. Sandia engineer Dean Rovang expects a laboratory result by late 2013. Sandia has already performed preliminary tests of the coils. Portions of the design are slated to receive their first tests this month and continue into early winter.
The team is already on the suspected problems. The potential ones already seen involve controlling instabilities in the liner and in the magnetic field that might prevent the fuel from constricting evenly, an essential condition for a useful implosion. Even isolating the factors contributing to this hundred-nanosecond-long compression event, in order to adjust them, will be challenging.
Sandia manager Daniel Sinars said, “Whatever the difficulties we still want to find the answer to what Slutz (and co-author Roger Vesey) propose: Can magnetically driven inertial fusion work? We owe it to the country to understand how realistic this possibility is.”
There will not be a history making result, though. As Sandia’s Z machine can bring a maximum of only 26 million amperes to bear upon a target, the researchers would be happy with a proof-of-principle result called scientific break-even, in which the amount of energy leaving the target equals the amount of energy put into the deuterium-tritium fuel.
This route would be fueled by deuterium-tritium available from seawater, the most plentiful material on earth.
Here’s the closing “Wow” statement the team gets from developing the simulations: the output demonstrated was 100 times that of a 60 million amperes input current. The output rose steeply as the current increased: 1,000 times input was achieved from an incoming pulse of 70 million amperes.
It seems there’s plenty of room for energy conversion from heat to electricity. Keep it going Sandia!