AN EBIS/RFQ - INJECTOR FOR A CANCER-THERAPY SYNCHROTRON

The electron beam ion source (EBIS) is an intense source of bare nuclei of light elements (C,N,O,Ne) for short pulses. A fast extraction time of 4-mu-s allows advantageous single turn injection into a medically dedicated synchrotron. Since the EBIS can provide bare nuclei of all light ions, it combines favorably with a 1.8 m long radio-frequency-quadrupole accelerator (RFQ) as the only LINAC needed for an injection energy of 1 MeV/u. The required intensity of 10(8) ions per pulse in 1 s is easily exceeded by a factor of 10 to compensate for beam losses. The technology of an EBIS with an electron current of 165 mA at 3 keV and 50 A/cm2 is well established and has proven to be very reliable for synchrotron injection over many years in Dubna, Saclay, and Stockholm. The low duty factor (10(-4)) of the RFQ, where 250 kW pulses of rf power will be applied for 25-mu-s, eliminates the need for cooling. Therefore a four-rod structure may be put on ceramic stands, biased with a negative high voltage to avoid high voltage on the source. The combination of an EBIS with a short RFQ may be considered as the least complex and most reliable injector solution for filling a cancer therapy synchrotron with fully stripped light ions.