Fast Ions

Energetic ions from heating or fusion that must stay confined to deposit their energy.

Fast ions — from neutral beams or fusion products — carry energy and current but can drive instabilities if not well confined. Their behaviour is a key part of heating and current-drive physics.

Fast ions from beams or fusion carry energy and drive current, but only if they stay confined long enough to slow down; if they escape early they waste heating and load the wall. They can also excite Alfvén and energetic-particle modes, so managing the fast-ion population is a real part of heating and, in D–T, alpha physics.