Slow beam extraction by a transverse RF field with AM and FM

Abstract A beam extraction method using a transverse rf electric field with amplitude and frequency modulation has been studied in order to develop an irradiation method which is synchronized with the breathing of a patient for high-quality charged particle therapy. The dependence of the extracted beam intensity on the voltage, the frequency band width and the center frequency of the transverse rf electric field has been investigated. The extracted beam intensity was slightly increased from that of the ordinary slow extraction method with a third order resonance. The response of the extracted beam intensity to the applied transverse rf electric field was as prompt as within 1 ms. The horizontal emittance of beams extracted by the present method was reduced by about 70% compared with that by the ordinary one due to utilizing a constant separatrix. Amplitude modulation can control the global beam spill structure. The frequency modulation reduced the effect of the current ripple of the main quadrupole magnets.