Compensation of the asymmetric phase–space distribution for a slowly extracted beam from a synchrotron

In ion beam cancer therapy, it is generally essential for a scanning-irradiation method and a rotating gantry system to deliver a circular beam profile with a Gaussian distribution. A slow beam extraction method utilized in a synchrotron ring, however, cannot deliver a beam with a Gaussian distribution in the horizontal phase space, because of its extraction mechanism. Furthermore, normally, the size of the horizontal emittance is much smaller than that of the vertical one. Thus, we have proposed a thin scatterer method in order to compensate for the phase–space distribution of a slowly extracted beam, although the emittance is slightly enlarged by scattering. As a result of particle tracking, we verified that the proposed method could change an asymmetric distribution to a Gaussian one in the horizontal phase space and realize a symmetric beam condition for the rotating gantry.