Noninvasive ion fraction quantification of dual-species beams in synchrotrons
The ion composition of dual-species beams in synchrotrons is typically inferred from invasive measurements performed after beam extraction. This paper introduces a complementary noninvasive method to determine the ion composition of such beams directly inside the synchrotron. The approach is applicable to low- and medium-energy synchrotrons and to small relative mass-to-charge ratio offsets, typically at the 1e-4 level. The method exploits dispersive orbit offsets between the two species and corresponding frequency corrections applied by the synchrotron RF radial regulation loop. This capability is of particular interest for ongoing research on online monitoring in carbon ion beam therapy using mixed 4He2+ and 12C6+ beams, which feature a relative mass-to-charge ratio offset of 0.065%. The proposed method is analytically derived and tested with particle tracking simulations using Xsuite. Its applicability under realistic experimental conditions is demonstrated at the MedAustron facility using mixed 4He2+ and 12C6+ beams. The results show good agreement with independent post-extraction measurements.