New inside out hover-magnet fusion reactor debuts at MIT

'Turbulent pincher' to bitchslap tokamaks, pellet-lasers?

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MIT boffins this week have taken the wraps off a new kind of nuclear fusion reactor, different from the humdrum tokamaks and laser-ignition chambers which have thus far offered such disappointing results.

The new kit is called the Levitated Dipole Experiment (LDX), and features a half-ton magnetic doughnut suspended in midair by super powerful force fields. The underlying principles were discovered by observing the behaviour of space plasma interacting with the magnetic fields of planets such as Jupiter.

Most Reg readers will be familiar with the idea of fusion reactors, intended to replace today's nuclear fission powerplants. Rather than splitting heavy atoms to release energy, fusion machines would instead fuse light ones together - the same process which powers the sun and stars. This would have major advantages: less radioactive waste and abundant fuel - the necessary isotopes could easily be obtained from sea water, by contrast with scarce and troublesome uranium. And the hysterical levels of security which surround fissionable fuels would be unnecessary, as fusion juice can't be made into an atomic bomb*.

On the day that working fusion reactors are developed, the world's energy problems are largely over: the non-fossil (low carbon) all-electric future can actually be delivered with the whole human race living at Western levels of luxury.

So much has been known for many decades, however. Despite much experimentation, a fusion reactor able to put out more energy than it consumes to run itself seems almost as far off as it did to start with. Most research thus far has focused on "tokamaks" - toroidal chambers intended to crush and heat a ring of plasma to fusion conditions using magnetic fields - and laser ignition, where a pellet of fuel is almost instantaneously brought to fusion by high powered laser blasts coming from all around it.

But now boffins at MIT and Columbia University have built the LDX, which seeks to exploit the phenomenon of "turbulent pinching" seen in space plasmas interacting with the magnetic fields of Earth and Jupiter. This has never been recreated in the lab.

The LDX's hovering dipole, made of superconducting coils housed inside a steel container, "flies" inside the larger chamber in which the experiment's plasma is held. It's intended to use "turbulent pinch" effects to squeeze superhot 10,000,000°C deuterium until it begins fusing into helium. Deuterium is more common than the tritium needed for more commonly-researched reactions, which could be a useful feature if the machine can achieve positive power output. For now, the dipole must draw its million-amp current from external sources.

According to Jay Kesner, MIT's LDX honcho, the difference between his baby and a regular tokamak is simple: with the tokamak the plasma is inside the magnet, whereas in the LDX the magnet is inside the plasma.

“It’s the first experiment of its kind,” he says, and “could produce an alternative path to fusion," though he cautions that other methods are likely to be operational sooner. Kesner sees the floating-dipole reactor as "second generation" kit, though even the first generation has yet to materialise thus far.

Kesner and allied boffins have just published a paper on LDX fusion in Nature Physics, here (subscription required). ®


*Admittedly fusion fuel is one ingredient for building an H-bomb, but you can only make one of those if you already have a working fission nuke to use as the trigger.

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