SLOW BEAM EXTRACTION BY A TRANSVERSE RF FIELD WITH AM AND FM

A beam extraction method using a transverse rf electric field with amp litude and frequency modulation has been studied in order to develop a n irradiation method which is synchronized with the breathing of a pat ient 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 inve stigated. The extracted beam intensity was slightly increased from tha t of the ordinary slow extraction method with a third order resonance. The response of the extracted beam intensity to the applied transvers e rf electric field was as prompt as within 1 ms. The horizontal emitt ance of beams extracted by the present method was reduced by about 70% compared with that by the ordinary one due to utilizing a constant se paratrix. Amplitude modulation can control the global beam spill struc ture. The frequency modulation reduced the effect of the current rippl e of the main quadrupole magnets.