bootstrap current is the electric current a toroidally confined plasma drives spontaneously through its own pressure gradient, reducing the external current drive a tokamak needs to sustain itself.
The effect was predicted by 📝neoclassical transport theory — Bickerton, Connor, and Taylor published the prediction in 1971 — and confirmed in tokamak experiments in the 1980s, a rare case of a subtle kinetic effect arriving on paper before it was seen in a machine. The mechanism runs through trapped particles: the population gyrating on 📝banana orbits carries an asymmetry set by the pressure gradient, and collisions transfer that imbalance of momentum to the freely circulating electrons, which then flow as a net toroidal current. The name is the point — the 📝plasma pulls itself up by its own bootstraps.
The consequence is strategic. A 📝Tokamak needs a large toroidal current to confine its plasma, but driving that current inductively from the 📝central solenoid is inherently pulsed, and external current drive is expensive in power. The bootstrap fraction grows with the pressure gradient, so a high-pressure plasma can supply much of its own current — the physics on which every steady-state tokamak concept leans.