The Extraction of Positively Charged Protons Beam from Cyclotron Due to Decreasing of the Energy at the Degrader
Abstract:
For modern medical cyclotrons, the acceleration of beams of negatively or positively charged protons is most widespread. As a rule, negatively charged ions are ex-traced from a cyclotron by recharging on a thin carbon foil. The method is easy in realization. However, to pro- duce negatively charged protons, a complex system of ex- ternal injection is usually used. Besides, the effect of Electromagnetic dissociation of an electron during acceleration limits the level of cyclotron magnetic field. Positively charged ions are produced by simple inter nal Penning type ion source and there are no limits in a magnetic field level. However, the extraction of such a beam from a cyclotron is possible only by a complex extraction system with an electrostatic deflector and passive or active focusing elements. At the paper the extraction of positively charged pro-ton beam by means of partial decreasing of energy at degrader is considered. The proposed method combines the positive features of described above schemes, such as easy of ions production, no limitation of the magnetic field level and an easy technical realization of extraction system. The obvious disadvantage of this method is the increasing of the beam emittance after passing through the degrader. As an example, a three-sector model cyclotron with a magnetic field level of 1 T to accelerate of positively charged protons to an energy of 15 MeV is proposed. The beam extraction is carried out due to 5 – 10% energy loss on a graphite degrader.
