A tiny amount of tungsten inside fusion plasma could roughly double the pressure needed to achieve ignition, according to a new theoretical model from the U.S. Department of Energy’s Princeton Plasma Physics Laboratory (PPPL).

The researchers found that tungsten at a concentration of just one part in 10,000 can significantly raise the conditions required for a plasma to sustain fusion reactions without continued external heating.

The study updates the Lawson criterion, a roughly 70-year-old benchmark used to determine whether a fusion plasma is hot and dense enough, for long enough, to reach ignition. The researchers incorporated several real-world effects that the original idealized criterion does not capture.

Their calculations also point to a potentially more energy-efficient route toward ignition. Instead of first increasing plasma density and then heating it, the model suggests heating the plasma first and raising its density afterward could provide a more efficient path.

“A lot of companies want to climb the mountain head-on and spend enormous energy to get there,” said PPPL physicist Luis Delgado-Aparicio. “Go around the peak instead. You reach the same place in a much smarter way, and you use far less energy.”

The researchers describe this route using a region called the Cordey saddle. It represents the lowest point on a boundary separating plasma that still needs external heating from plasma capable of sustaining its own burn.

In an ideal plasma containing only fusion fuel, the model places this point at a fusion gain, or Q, of about 5. That means the plasma produces roughly five times as much fusion power as the external heating power supplied.

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