Intensity control in RF-knockout extraction for scanning irradiation

In cancer therapy using an ion beam, a scanning irradiation method has been developed in order to realize 3-D conformal irradiation. From studies of the scanning method, it has been required for a medical synchrotron to be capable of controlling the beam intensity during the duration of extraction. For this purpose, a beam-intensity control technique with RF-knockout slow-extraction has been studied and developed at the HIMAC synchrotron. Based on a simple one-dimensional model of extraction, the function of amplitude modulation (AM) for a transverse RF-field was analytically calculated to control the beam current. By cooperating with the feedback system, finally, we could control the beam intensity within a range of one order during a single flattop. We report on a simulation and the experiment result of intensity control for scanning irradiation.