Scientists from the Swiss Associate CRPP, Lawrence Livermore National Laboratory and Princeton Plasma Physics Laboratory received the renowned R&D 100 award 2012 for developing the snowflake power divertor. The technique could be the solution to one of the biggest obstacles on the road to fusion power.

Handling plasma exhausts is, today, considered to be one of the most important unsolved problems on the road to a fusion power plant. In a fusion reactor, magnetic fields keep the plasma away from the reactor wall in order to allow the high temperatures needed for fusion reactions to be achieved. The most promising magnetic field configuration so far forms two open magnetic field lines which guide the outer – cooler – plasma layer to a dedicated area, the divertor, where it is removed. Designing materials that are strong enough to withstand this heat flux is an important challenge in fusion research. The snowflake technique has the potential to reduce the heat at the divertor by 50 percent. It thus opens up a way to create heat loads that can be tolerated by existing materials.

The snowflake divertor employs a more advanced magnetic field configuration which produces four ‘legs’ – open magnetic field lines – instead of the usual two, linking the hot plasma to the divertor. The plasma is flared at the divertor surface and the residual heat flux per wall area is reduced. The name “snowflake” stems from the six fold pattern formed by the magnetic field lines.

The theory of the concept was developed by Lawrence Livermore National Laboratory (LLNL) and the first snowflake configuration in fusion plasmas was then created at CRPP in the tokamak TCV. TCV is a worldwide unique tokamak in terms of its flexibility to shape the plasma. It is equipped with 16 independent magnetic coils and is capable of implementing innovative configurations such as the snowflake. The snowflake divertor concept has also been implemented at the Princeton Plasma Physics (PPPL) tokamak NSTX. Both experiments confirm that the technique is a valid concept enabling the reduction of the heat load at the divertor.

Since 1963, the R&D 100 award has been internationally recognised as a benchmark for excellence in various areas of industry and science. An independent panel of experts, along with the US R&D magazine annually selects the 100 most significant technological advances. In the past, it has been awarded to inventions such as the halogen lamp, the fax machine, or, more recently, HD television.