Experiments inside a fusion reactor in China have demonstrated a new way to circumvent one of the caps on the density of the superheated plasma swirling inside.

At the Experimental Advanced Superconducting Tokamak (EAST), physicists successfully exceeded what is known as the Greenwald limit, a practical density boundary beyond which plasmas tend to violently destabilize, often damaging reactor components.

For a long time, the Greenwald limit was accepted as a given and incorporated into fusion reactor engineering. The new work shows that precise control over how the plasma is created and interacts with the reactor walls can push it beyond this limit into what physicists call a 'density-free' regime.

Fusion reactors are designed to replicate the intense nuclear fusion that occurs in the heart of the Sun, generating vast amounts of energy. There are a number of significant barriers to overcome – one of which is plasma density.