Development of a compact electron-cyclotron-resonance ion source for high-energy carbon-ion therapy

Ion sources for medical facilities should have characteristics of easy maintenance, low electric power consumption, good stability, and long operation time without problems (one year or longer). For this, a 10 GHz compact electron-cyclotron-resonance ion source with all-permanent magnets (Kei2 source) was developed. The maximum mirror magnetic fields on the beam axis are 0.59 T at the extraction side and 0.87 T at the gas-injection side, while the minimum B strength is 0.25 T. These parameters have been optimized for the production of C4+ based on the experience at the 10 GHz NIRS-ECR ion source and a previous prototype compact source (Kei source). The Kei2 source has a diameter of 320 mm and a length of 295 mm. The beam intensity of C4+ was obtained to be 530 mu A under an extraction voltage of 40 kV. The beam stability was better than 6% at C4+ of 280 mu A during 90 h with no adjustment of the operation parameters. The details of the design and beam tests of the source are described in this paper. (c) 2005 American Institute of Physics.