The condition for toroidal experiments to become energetically self-sustaining is examined and a simple relationship is given between the self-ignition temperature and the plasma current. The temperature is limited at low density by synchrotron radiation and at high density by βθ-limitations. Tokamaks could, in principle, reach ignition conditions on Ohmic heating alone but will probably be limited by synchrotron radiation. A quite modest additional heating source allows ignition at higher density and the consequent examination of βθ limitations. The power and energy requirements for neutral beam heating are examined and shown to be compatible with existing technology.
A comparison of energy confinement in tokamaks and stellarators