Pure bismuth samples were irradiated at 20 K with swift heavy ions from 18O to 238U in the GeV range. The rate of the induced damage was deduced from in situ electrical resistance measurements. Above a threshold in the electronic stopping power Se equal to 24 keV nm-1, the damage is due to electronic slowing down. Above 30 keV nm-1, the electronic slowing down is efficient enough to induce latent tracks attributed to the appearance of a high-resistivity phase. The induced latent tracks radii can be up to 21.9 nm for Se=51 keV nm-1 which is the largest value reported so far for non-radiolytic materials. The evolution with Se of the latent tracks radii is calculated on the basis of the thermal spike model, assuming a realistic value for the electron-phonon coupling constant. A rather good agreement is obtained which supports the idea that the thermal spike could be operative in the observed radiation damage.

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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).

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