Nuclear fusion nears efficiency break-even

Posted by Kate Taylor

Nuclear fusion is very close to the point where the amount of energy produced by the system equals or surpasses what's been put in.

Sandia scientists say that magnetically imploded tubes called liners, intended to help produce controlled nuclear fusion at scientific "breakeven energies or better, have functioned successfully in preliminary tests.

It's a key test of a concept called Magnetized Liner Inertial Fusion (MagLIF),based on magnetic fields and laser pre-heating.

In the dry-run experiments, cylindrical beryllium liners remained reasonably intact as they were imploded by the huge magnetic field of Sandia's Z machine, the world's most powerful pulsed-power accelerator.

This means they were capable of combining nuclear fuels - deuterium and possibly tritium - to the point of fusing them. Sandia researchers expect to add deuterium in experiments scheduled for 2013.

"The experimental results - the degree to which the imploding liner maintained its cylindrical integrity throughout its implosion - were consistent with results from earlier Sandia computer simulations," says lead researcher Ryan McBride."These predicted MagLIF will exceed scientific break-even."

Simulations have shown that an accelerator generating 60 million amperes or more could reach high-gain fusion conditions, where the fusion energy released exceeds the energy supplied to the fuel by more than 1,000 times.

The liner is intended to contain fusion fuel and push it together in nanoseconds. However, the metallic liner doing the compressing is also being eaten away as it conducts the Z machine's enormous electrical current along its outer surface. It begins to vaporize and turn into plasma, in much the same way as a car fuse vaporizes when a short circuit sends too much current through it.

"The question is, can we start off with a thick enough tube such that we can complete the implosion and burn the fusion fuel before the instability eats its way completely through the liner wall?" says McBride.

While a thicker tube would be more robust, the implosion would be less efficient because Z would have to accelerate more liner mass. A thinner tube could be accelerated to a much higher implosion velocity, but then the instability would rip the liner to shreds.

"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," says Mcbride.

Next year, the team plans to take the next step of integrating in the new magnetic field and laser preheat capabilities that will be required to test the full concept.

"This work is one more step on a long path to possible energy applications," adds Sandia senior manager Mark Herrmann.