PPPL model: heating plasma before raising its density could cut energy needed for fusion ignition

Researchers at the Princeton Plasma Physics Laboratory (PPPL) in the United States have identified a potentially much less energy-intensive way to start and sustain fusion reactions, Futura Sciences reports. futura-sciences.comFutura Sciencesfutura-sciences.comOpen source ↗ The study, "Generalized Lawson-Cordey-Mills Accessibility of Fusion Ignition", was published in Physical Review Letters. Its result rests on a theoretical model, not on an experimental demonstration.

Fusion reproduces the internal mechanism of the Sun. Light nuclei, usually deuterium and tritium, fuse at extremely high temperatures and release large amounts of energy. The ultimate goal is ignition: the point at which the plasma produces enough heat to sustain the fusion reactions by itself.

Heating first, densifying later

Fusion requires a temperature of 100 to 150 million degrees Celsius inside the reactor. The traditional method is to confine the hot plasma with powerful magnetic fields, raise its density, and only then heat it further. The PPPL team suggests reversing this order: heat the plasma first, then increase its density gradually. According to the authors, this reaches the same result with much less energy.

To find this route, the team revisited the Lawson criterion, formulated in the 1950s, which defines the temperature, density and confinement conditions needed for profitable fusion. They extended the model by including four complicating phenomena at once: the buildup of helium ash, impurities from the reactor walls, synchrotron radiation losses and heat leaks. futura-sciences.comFutura Sciencesfutura-sciences.comOpen source ↗

Tungsten walls as a constraint

The study also gives a warning. Tungsten, the metal chosen to withstand the extreme temperatures at reactor walls, could become an obstacle to ignition. According to the researchers' calculations, contamination of about one tungsten atom per 10,000 plasma particles is enough to double the pressure needed to trigger fusion.

This matters because several next-generation reactors will have tungsten walls. The authors propose countermeasures, including an internal coating of liquid lithium to keep tungsten from migrating into the plasma.

Futura Sciences notes that fusion power plants are still many years away from replacing current reactors, in part because the results come from a theoretical model rather than an experiment. futura-sciences.comFutura Sciencesfutura-sciences.comOpen source ↗