Scientists may have found a shortcut to fusion energy
Princeton Plasma Physics Laboratory may have found a dramatically more efficient route to fusion energy by reversing the traditional approach: heating plasma first, then increasing its density. Their calculations could help future reactors reach self-sustaining fusion with far less energy while avoiding hidden problems that make ignition harder.
Key points
- PPPL physicists have developed an expanded version of the Lawson criterion that maps a potentially more energy-efficient route to fusion ignition.
- Their calculations suggest heating plasma before increasing its density could reach ignition with far less energy than the conventional density-first sequence.
- The work is theoretical and not yet tested experimentally, and the team plans computer simulations to explore the approach further.
Scientists at the U.S. Department of Energy's Princeton Plasma Physics Laboratory (PPPL) have identified a potentially more efficient way to reach fusion ignition. Physicists Luis Delgado-Aparicio, Masayuki Ono and Jonathan Menard developed a more comprehensive version of the Lawson criterion, the long-used equation defining the conditions for a self-sustaining fusion reaction, and published the findings in Physical Review Letters.
The new calculations suggest that changing the order in which plasma is heated and compressed could substantially reduce the energy needed for ignition. Instead of raising plasma density first and then supplying enormous heat, researchers could heat the plasma before making it denser.
A different route to ignition
Delgado-Aparicio compared the energy requirements for ignition to a landscape dominated by a towering mountain, with the destination on the other side reachable by several routes. Many proposed strategies try to climb straight over it, raising density first and then adding the heat needed to reach ignition.
The team's calculations point to a different sequence as considerably more efficient. Delgado-Aparicio said, "Go around the peak instead," adding that the same place is reached with far less energy. The researchers identified a key region called the Cordey saddle, a relatively accessible point along the boundary between plasma that needs outside heating and plasma that can sustain its own fusion reactions.
A lot of companies want to climb the mountain head-on and spend enormous energy to get there
— Luis Delgado-Aparicio
Tungsten and the limits of models
The study also examined tungsten, a heat-resistant metal chosen for the interior walls of more than a dozen next-generation fusion machines. The team's calculations show that tungsten contamination at a concentration of just one part in 10,000 can roughly double the pressure required to achieve ignition.
The calculations were first done in two dimensions; extending them to three dimensions showed the pressure needed for ignition could exceed the limits at which plasma remains stable. The proposed heat-first approach has not been demonstrated experimentally, and existing experiments have not reached the temperatures associated with the Cordey saddle. The PPPL team plans digital experiments to test whether heating plasma before increasing its density delivers the expected advantages.
