US researchers solve tokamak plasma mystery with elusive ‘voids’ discovery

Researchers at the University of California, San Diego, have developed a new theoretical model that may explain a longstanding discrepancy in nuclear fusion research related to plasma behavior at the edge of tokamak reactors. The study, led by physicists Mingyun Cao and Patrick Diamond, focuses on the plasma boundary—a critical region for sustaining fusion reactions and protecting reactor components from extreme heat. Previous simulations underestimated the width of the turbulent layer at the plasma edge, a problem known as the “shortfall problem,” which has hindered accurate predictive modeling of plasma dynamics. The breakthrough centers on previously overlooked structures called “voids,” which are inward-moving, density-depleted formations at the plasma edge. While past research emphasized outward-moving, density-enhanced “blobs,” the role of voids remained unclear. Cao and Diamond’s model treats voids as coherent, particle-like entities that, as they move from the cooler plasma edge toward the hotter core, generate plasma drift waves by interacting with steep temperature and density gradients. These waves transfer