Physical Design of High Mass Resolution Spectrometer for ISOL

High mass resolution spectrometer for isotope seperator on line(ISOL) in Beijing radioactive ion－beam facilities(BRIF) project requires mass resolving power of 20 000. A bi－energy system with big and small dipoles is used to reduce energy dispersion which is too large to get mass resolving power. When the width of beam with a Gaussian distribution is 0.06 mm and 10 mrad, resolving power of this spectrometer is 33 400. After consideration of 0.002% energy spread introduced by acceleration, the final resolving power of this spectrometer reaches 20 000.