What it is
The Greenwald limit is an empirical ceiling on tokamak plasma density above which the plasma typically disrupts. On the EAST superconducting tokamak, researchers used electron-cyclotron-resonance-heating-assisted ohmic start-up with high initial neutral density to reach line-averaged densities of 1.3 to 1.65 times the Greenwald density, well above the device's usual range of 0.8 to 1.0. That is 30 to 65 percent above the empirical limit, and the plasma stayed stable rather than disrupting.
Why it matters
High density is essential for a tokamak to reach energy breakeven and a burning plasma, so the Greenwald limit has long been treated as a hard operational wall. Sustaining stable operation 30 to 65 percent above it suggests the limit is not fundamental but depends on how the plasma edge is set up. The experiments landed in a density-free regime predicted by a recent plasma-wall self-organization theory, giving the result a mechanistic explanation rather than being a lucky operating point.
Underlined numbers link to their source. Every metric and quoted figure is listed under Sources and data below.
Filed undernuclear fusion, tokamak, Greenwald limit, plasma physics, EAST