Dynamique de l'éjection lente et son influence sur les lignes de transfert

The treatment of cancer with accelerator beams has a long history with linacs, cyclotrons and now synchrotrons being exploited for this purpose. Treatment techniques can be broadly divided into the use of spread-out beams and scanned 'pencil' beams. The Bragg-peak behaviour of charged hadrons makes them ideal candidates for the latter. The combination of precisely focused 'pencil' beams with controllable penetration (Bragg peak) and high, radio-biological efficiency (light ions) opens the way to treating the more awkward tumours that are radio-resistant, complex in shape and lodged against critical organs. To accelerate light ions (carbon) with pulse-to-pulse energy variation, a synchrotron is the natural choice. The beam scanning system is controlled via an on-line measurement of the particle flux entering the patient and, for this reason, the beam spill must be extended in time (seconds) by a slow-extraction scheme. The quality of the dose intensity profile ultimately depends on the uniformity of the beam spill. This is the greatest challenge for the synchrotron, since slow-extraction schemes are notoriously sensitive. In this thesis, the resonant slow extraction is studied in detail both in its temporal and transverse aspects. The results from this study indicate which extraction scheme, among the various possibilities, is to be preferred for an application requiring smooth spills. The extracted beam distribution in the transverse phase spaces is also of interest for the dose distribution system and for treatment planning. Armed with a detailed knowledge of the beam characteristics from the slow extraction a novel approach to transfer line design, that copes better with the asymmetry and special phase space distributions, is described and possible implementations of the theoretical ideas are given as examples.