Researchers at the U.S. Department of Energy's (DOE) Princeton Plasma Physics Laboratory (PPPL) have challenged understanding of a key element in fusion plasmas. At issue has been an accurate prediction of the size of the "bootstrap current" -- a self-generating electric current -- and an understanding of what carries the current at the edge of plasmas in doughnut-shaped facilities called tokamaks. This bootstrap-generated current combines with the current in the core of the plasma to produce a magnetic field to hold the hot gas together during experiments, and can produce stability at the edge of the plasma.
The recent work, published in the April issue of the journal Physics of Plasmas, focuses on the region at the edge in which the temperature and density drop off sharply. In this steep gradient region -- or pedestal -- the bootstrap current is large, enhancing the confining magnetic field but also triggering instability in some conditions.
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