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ScienceWise - Spring 2011

Pinching the plasma

Article Illustration
Dr Cormac Corr and the MDF facility

Developing advanced materials to solve the energy crisis

The world is facing an energy crisis as increasing population and urbanisation consume fossil fuels at an exponential rate. Aside from their undesirable carbon footprint, fossil fuels like oil also look set to run out within this century. To make matters worse, recent events in Japan have deeply shaken public confidence in the nuclear industry and humanity’s ability to deal with the highly toxic waste from conventional fission reactors.

However amidst this rather gloomy picture there is some positive news. International efforts to harness fusion power – the process of fusing two hydrogen-like nuclei to create helium – are well in progress. The world’s first practical fusion power plant ITER is currently being built in Southern France by an international scientific consortium.

It is projected that ITER will generate 500 megawatts of power whilst requiring only 50 megawatts to create the plasma. Its fusion reactions will emit no greenhouse gasses and perhaps most importantly, will generate no long lived radioactive waste to pose a contamination threat to the environment. However, the technological challenge of designing and building such a device is daunting.

One particularly challenging aspect of designing a reactor like ITER is finding a suitable material for the walls of the reaction chamber. Although the pressure inside is low and the intensely hot plasma is kept out of physical contact with the wall by the magnetic containment field, energetic by-products of the fusion process irradiate the wall with great ferocity.

Such energetic particles smashing into materials like metals create two problems. Firstly the impacts degrade the wall material by both chemical reactions and by sputtering atoms out of the wall like a snooker ball hitting the pack. Secondly, these secondary atoms and ions that are sputtered out of the wall mix with the fusion plasma disrupting the flow and cooling it, both effects being detrimental to the efficiency of the reactor.

One scientist working on just this problem is Dr Cormac Corr who heads up the Plasma Surface Interaction group within the Plasma Research Laboratory at the Australian National University. “Really this boils down to a materials science problem,” Dr Corr explains, “ We need to develop new exotic materials that can better withstand these extreme environments.” Dr Corr’s research applies a helicon generated plasma system, initiated and designed by Dr. Boyd Blackwell in collaboration with colleagues from Oak Ridge National Laboratories, which can mimic the incredibly harsh conditions experienced inside a fusion reactor.

This prototype plasma system known as the Material Diagnostic Facility, MDF, generates a very high-density hydrogen plasma which is then accelerated towards the material test target. Looking something like a ray gun from a Flash Gordon movie, the MDF uses a series of magnetic coils to create a field gradient called a magnetic focus that acts like a lens on the plasma stream. Just as an electron microscope focuses electrons onto a sample, the magnetic field focuses the plasma beam into a single intense energetic spot. This mimics the very conditions that will exist at the internal walls of fusion reactors of the future.

“Essentially we’re trying to unfold the synergistic effect of plasma and ion bombardment at the plasma-wall interface. We want to do that in a controlled environment in which we can use advanced diagnostics to really understand the underlying science of what’s going on.” Dr Corr says.

The diagnostics on the MDF include optical spectroscopy and sophisticated ion probes that give  scientists information on the types of  particles sputtered out, their energy and how they are interacting with the plasma in the chamber.  The MDF is a part of the Australian Plasma Fusion Research Facility, available to researchers through the Australian Institute of Nuclear Science (ANSTO) and Engineering or by collaboration with Plasma Research Laboratory staff.

As part of the recently announced collaborative agreement between ANU and ANSTO, researchers at the Institute of Materials are providing materials research expertise and developing a target chamber for MDF.  

“Advanced materials is an area in which Australia can really make a significant contribution to the international fusion efforts,” Dr Corr says, “Using the expertise here and at ANSTO  we have the capability to develop smarter, better materials for such harsh environments.”  “It’s difficult to predict the outcome of research, but we’re hoping that we might be able to develop materials whose properties actually improve when irradiated perhaps even self organising or self repairing.”

Of course fusion power is by no means the only application for such materials. Spacecraft and satellites are constantly bombarded by the energetic particles in the solar wind and frequently suffer damage as a result. Such better radiation resistant materials may also lead to longer, better and more ambitious space missions.

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