Magnetic plasma plucking helps control fusion heat bursts

Researchers in the US have discovered how potentially damaging heat bursts inside the type of nuclear fusion reactor being built for the Iter experiment in Southern France can be controlled. This discovery could prolong the duration of fusion reactions, bringing steady-state fusion a stage nearer, the team hopes.

Tokamak reactors - where the hot plasma that undergoes nuclear fusion is constrained by magnetic fields inside a toroidal vacuum chamber - suffer from an effect known as ELMs (edge-localised modes), where the plasma becomes unstable near the edge of the chamber. This can damage the walls of the chamber, especially at the base where the waste products of fusion are removed.

A team from the US Department of Energy’s Princeton Plasma Physics Laboratory (PPPL), working on the DIII-D tokomak at General Atomics’ San Diego facility, discovered some years ago that ELMs could be suppressed with magnetic fields much smaller than those that confine the plasma, which seemed to allow the edge of the plasma to release heat slowly rather than in a damaging burst. A new team, led by Carlos Paz-Soldan of General Atomics, now believes they have discovered how this happens.