Abstract:
Radioisotopes for nuclear medicine can be produced either by nuclear reactors or accelerators.
Commercial cyclotrons (E = 15-70 MeV) achieve currents up to or just above 1 mA. Both proton and H- cyclotrons are used.
One of the decisive issues in the design and operation of cyclotrons is the choice of the beam extraction method. Typical methods are extraction by electrostatic deflector and by stripping.
The electrostatic deflector strongly limits the maximum beam intensity because of losses and induced heat-load on its septum. The latter method requires acceleration of H- beams which are sensitive for rest gas and Lorentz stripping and therefore require good vacuum and not too high magnetic field.
The self-extracting cyclotron is a promising tool for large-scale production of medical radioisotopes. The 14 MeV H+ machine uses an internal ion source and a magnetic field that features a sharp transition from the stable isochronous zone to the unstable fringe field, allowing spontaneous beam extraction. First harmonic coils increase the turn-separation at the entrance of the extraction path.
In 2000 a prototype build by the IBA company provided the proof-of-principle for self-extraction by the extraction of a proton current close to 2 mA.
Recently, a simulation study has been done to improve the concept of self-extraction. Proton currents up to 5 mA are aimed for from the improved self-extracting cyclotron called InnovaTron.
A major variable of the beam simulations is the space charge effect in the cyclotron centre.
An approach has been developed for a more accurate simulation of the beam extracted from the ion source and its acceleration in the first accelerating gaps under space charge conditions.
The main features of the InnovaTron cyclotron are presented together with detailed results obtained for central region studies including space charge in beam dynamics simulations.