Nuclear Fusion: Simulation Shows Potential

Experimental nuclear fusion reactor is seen at a laboratory in the Southwest Institute of Physics in Chengdu, Sichuan Province April 15, 2011.

High-gain nuclear fusion could soon be a possibility according to new computer simulations.

A series of computer simulations performed at Sandia National Laboratories revealed that a fusion reactor can release an output of energy that is greater than the energy fed into the reactor.

The method being tested at Sandia appears to be 50 times more efficient to drive implosions of targeted materials to create the fusion reaction.

Nuclear fusion occurs when two atoms fuse together to form a heavier atom. This process releases a vast amount of energy. However nuclear fusion only occurs naturally at incredibly high temperatures like the center of a star.

Even though the process has been impossible to recreate in Earth, scientists have been studying ways to make nuclear fusion possible because nuclear fusion is a very attractive power source since the fuel is free and the process releases massive amounts of energy.

Scientists have looked at two competing approaches for the artificial creation of nuclear fusion: magnetic confinement and inertial confinement.

Magnetic confinement uses magnetic force to contain the fusing plasma within a device while inertial confinement uses lasers to trigger the fusion process.

Magnetic confinement is being used in the 500-megawatt ITER fusion reactor in France while inertial confinement is being used in California's National Ignition Facility.

Magnetic confinement is regarded as the better alternative and according to the computer simulations performed at Sandia the method is more efficient as well.

The researchers at Sandia are testing a method called magnetized inertial fusion in which two coils generate a magnetic field that confines the fusion reaction.

A metal cylinder lines the insides of each of the coils. The cylinder has a metal liner of deuterium and tritium which is then hit with a current of tens of millions of amperes. The current destroys the liner but it generates a strong magnetic field.

"People didn't think there was a high-gain option for magnetized inertial fusion but these numerical simulations show there is," said Sandia researcher Steve Slutz, the paper's lead author. "Now we have to see if nature will let us do it. In principle, we don't know why we can't."

The computer simulations showed that the output was 100 times that of 60 million amperes put into the system. Actual tests are necessary to validate the computer simulations and they are already under way at Sandia. A laboratory result is expected by late 2013.

The work was reported in the January 13 issue of Physical Review Letters and was supported by Sandia's Laboratory Directed Research and Development office and by the National Nuclear Security Administration.

Alternative Sources of Energy: Acoustic Cavitation Fusion

Scientists the lure of thermonuclear fusion has been incredibly attractive. Thermonuclear fusion held the promise of cheap, clean and unlimited energy.

Research in the field has split into many disciplines, one of these is the experiments in the hot fusion field called "acoustic inertial confinement fusion."

The idea of acoustic fusion is derived from the phenomenon called cavitation. Cavitation occurs when a liquid is exposed to rapid changes in pressure which causes the formation of gas or vapor bubbles.

An acoustic field sends pressure waves through the fluid causing the bubbles to grow and collapse and produces visible flashes of light. The researchers studying the light emitting bubbles speculate that the temperature and pressure of the gas inside bubbles could trigger a fusion reaction.

The tiny bubbles could produce the same effect as that found on the surface of the Sun and could one day be a new energy source.

While the concept has been proven in desktop experiments it's in real life applications that researchers of acoustic fusion run into problems. Building a fusion reactor that generates more energy that it consumes is particularly challenging and many skeptics question whether desktop experiments could work in the real world.

Compared to other forms of fusion power being researched today like magnetic and laser inertial confinement fusion, acoustic fusion requires inexpensive equipment, facilities and materials.

Acoustic fusion is relatively simple and its commercial success could be achieved in the next few years. One company, Impulse Devices has been exploring acoustic fusion and has pioneered the use of Extreme Acoustic Cavitation.

According to Dr. Wylene Dunbar, CEO of Impulse Devices Inc., the company's unique technology generates strong acoustic cavitation but still requires only a few hundred watts of electric power. Impulse's technology has achieved "proof of concept" in several areas and the company is working with several industrial partners to integrate its technology into their processes.

If acoustic fusion works it could provide clean energy for generations to come.

All you need to know about Laser Fusion

There's a big new kid on the nuclear energy block.

Last week British firm AWE (formerly the Atomic Weapons Establishment), based in Aldermaston, the Rutherford Appleton Laboratory in Harwell, UK, and the Lawrence Livermore National Laboratory in California said they would team up to develop laser fusion as a clean energy source.

Laser fusion is an alternative to magnetically induced nuclear fusion, which is used in the Joint European Torus (JET) now operating in Culham, UK, and the test reactor ITER, under construction in Cadarache, France.

Historically, laser fusion has been used focused mostly for weapons testing, while power generation research has concentrated on magnetic fusion. Is that about to change?

What is laser fusion?
At high temperatures and pressures, the nuclei of the heavy hydrogen isotopes deuterium and tritium form a plasma and can be fused to form helium, releasing energy and a neutron.

Firing a synchronised barrage of laser pulses can vaporise the surface of a pellet filled with these isotopes, forcing the pellet to implode and so producing fusion conditions inside the pellet for a few billionths of a second.

The physics resembles the detonation of a thermonuclear (or hydrogen) bomb – although on a much smaller scale – and so the US has used laser fusion to simulate these explosions.

What advantages does it have over magnetic fusion?
Magnetic fusion reactors zap heavy hydrogen gas with a powerful electrical pulse to produce a plasma. A strong magnetic field is then required to confine the plasma before fusion can take place.

That's hard, because plasmas can quickly leak or become unstable. By contrast, laser fusion produces much higher temperature and pressures, so fusion occurs faster, and the plasma must be confined for only billionths of a second.

Fusion of either kind is attractive as a power source because the fuel is more abundant than uranium, and the process does not produce the highly radioactive isotopes generated by splitting uranium atoms.

What stage is the tech at, and who is working on it?
Laser fusion has been studied since the 1960s, with most US funding coming from the nuclear weapons programme.

Today's biggest fusion laser is the National Ignition Facility (NIF) at Livermore. By the end of next year, Livermore hopes to reach "ignition" by producing more energy from fusion than is needed to generate the laser pulse.

Smaller lasers are used in fusion programmes at Rutherford Appleton, the University of Rochester in New York and Osaka University, Japan; France is building a NIF-sized system called Megajoule Laser. ITER, meanwhile, is a decade from igniting magnetic fusion.

When will laser fusion come to the power grid?
Livermore's Mike Dunne says that if all goes well, a plant delivering about 440 megawatts of electricity could be up and running in a decade; full-scale versions that follow would deliver about 1000 megawatts.

But don't hold your breath. "So far this is at the border of science fiction," says Hans Kristensen, director of the nuclear information project of the Federation of American Scientists. "The technological hurdles are not nearly explored yet."

Is there anything I need to worry about?
Laser fusion reactors will not have a large volume of hot material that might melt down if power failed, as occurred at the Fukushima Daiichi plant in Japan earlier this year. But fusion neutrons are hazardous and will make other materials in the reactor radioactive.

The tritium in the fuel is also radioactive: it emits beta particles so is dangerous if inhaled and has a half-life of 12.5 years.

Giant Laser set to trigger Fusion Reaction

The world's largest laser is approaching the long-sought goal of igniting a fusion reaction that produces more energy than the laser delivers.

Lasers are intended to do this by super-heating a fusion fuel pellet until it implodes, heating and compressing its central core to the temperatures and pressures needed for nuclear fusion.

Past experiments have been plagued by irregular implosions that wasted most of the input energy. But now, researchers led by Brian MacGowan of the Lawrence Livermore National Laboratory in California have managed to squeeze targets of material into spheres rather than pancakes or more lopsided shapes, paving the way for future attempts at fusion.

The work was performed at Livermore's 192-laser beam National Ignition Facility (NIF), which began operating in 2009.

The team used targets that did not contain the key ingredients for fusion – two isotopes of hydrogen known as deuterium and tritium. But the symmetrical implosion of the targets suggests that NIF should be able to ignite fusion with laser pulses of 1.2 to 1.3 megajoules – well below its full 1.8-megajoule capacity.

"From everything we can see, we're on the right path here," Jeff Wisoff, a top NIF manager told New Scientist.

Researchers spent last year slowly cranking up the output of the laser, ultimately reaching a total energy of more than 1 megajoules. Now they're pausing to mount new instruments on the 10-centimetre-thick aluminium target chamber and to install giant concrete doors to contain neutrons they expect to produce in future fusion experiments.

In a few months, they will begin testing a series of new targets designed to assess beam interactions and compression. If all goes well, they could try for fusion ignition by the end of the year.