A research team from the US Department of Energy’s Sandia National Laboratories has discovered a way to keep the fusion plasma from eroding divertor walls inside tokamak fusion machines.
The researchers believe that this could enable them to achieve "scientific breakeven" (i.e. the amount of energy produced by the reactor is greater than the energy input) within two or three years – a "holy grail" of nuclear fusion development which has not yet been achieved..
The tokamak method is one of the most promising technologies for producing nuclear fusion. In a tokamak fusion machine, up to several million amps of electricity flows through the doughnut-shaped plasma made of deuterium and tritium. A strong magnetic field confines the plasma while high-energy particle beams or radio waves heat it to more than a hundred million degrees celsius when it fuses to produce helium and release energy.
Plasma at the outer boundary flows into a separate chamber where it strikes the divertor surface. The divertor prevents plasma from striking the chamber walls and generating impurities that would cool and contaminate the main plasma.
As the divertor walls are in direct contact with the energy-producing fusion plasma, they quickly become eroded. Erosion increases the need to replace components, contaminates the plasma and deposits material in undesirable places.
The Sandia researchers injected deuterium gas into the plasma in the divertor. This cooled the plasma near the divertor surface to the point at which erosion does not occur because the particles hitting the suface do not have sufficient energy.
One or the researchers, Bill Wampler, said that "our preliminary results show detached plasma operation provides an effective way to eliminate erosion in the divertor. We may have resolved a major problem in fusion.”