Control of the slow extraction process in a dedicated proton synchrotron for hadron therapy

The ring design of the synchrotron for cancer treatment, based on the third-order resonant extraction, was been performed to meet the special medical requirements. The uniformity of the slow extracted beam from the proton synchrotron is the main requirement on the beam quality determined by the medical application. The smooth extraction during at least 400 msec should be realized for the `raster' scanning of tumours. Control of the slow extraction over the whole spill time is discussed in this report. To keep all lattice functions of the ring constant during the extraction a slow movement of the accelerated particles into the resonance can be used. To reduce degradation of the uniformity of the extracted beam by ripples from the power converters of the magnetic elements, the RF empty-bucket channeling method should be utilized. This method allows reduce the ripple influence during slow extraction. Both methods are analyzed to control the slow extraction for the dedicated proton synchrotron. The main parameters of the betatron core for this machine are determined. To realize the `empty-bucket' technique, the RF system of the synchrotron can be used with the maximum voltage at least 1.5 kV. The influence of the high-frequency ripple on the multiplying factor and the duty factor of the spill is studied. (4 refs).