A simple global-balance model shows the possibility of reaching the ignition of a low-density (3 − 4 × 1013 cm−3) tokamak reactor. This requires the use of fast-neutral injection at already achievable energy (100 keV). With the help of their complete cylindrical code, the authors have found for a typical reactor (q = 1.5) that the total injected power has to be about 25 MW. To increase the density up to about 1014 cm−3, the authors propose the use of a moving limiter, the plasma radius being increased from 90 to 300 cm during about 10 s. Plasma ignition is still possible with fast-neutral injection of similar energy. The total injected power for a reactor with q = 3 has been found to be about 80 MW. This power decreases if during expansion q changes from q = 3 (a = 90 cm) to q = 2 (a = 300 cm).