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).

Ab initio calculations of the five-fold differential cross sections for electron-impact double ionization of thymine, cytosine, adenine and guanine are performed in the first Born approximation for an incident energy close to 5500 eV. The wavefunctions of the DNA bases are constructed using the multi-center wave functions from the Gaussian 03 program. These multicenter wave functions are converted into single-center expansions of Slater-type functions. For the final state, the two ejected electrons are described by two Coulomb wave functions. The electron-electron repulsion between the two ejected electrons is also taken into account. Mechanisms of the double ionization are discussed for each case and the best choices of the kinematical parameters are determined for next experiments.

No abstract