Towards the detection of mixed helium and carbon ion beams using a gas-filled charge exchange cell

Irradiation with mixed helium and carbon ion beams is emerging as a promising approach to treatment monitoring in ion radiotherapy. In contrast to mono-isotopic beams, the full characterization of the mixed beam requires distinguishing ion species of almost identical charge-to-mass ratio, which is not feasible with most conventional beam diagnostic devices. This proceeding proposes a measurement concept that could allow for determining the ion mixing ratio after extraction from the ion source at energies around 10 keV/u. The concept relies on a gas-filled charge exchange cell, where the traversing ions experience electron capture events, followed by an electrostatic or magnetic analyzer and beam intensity measurement. The proposal is accompanied by proof-of-concept measurements performed at the *Helmholtz Zentrum Dresden-Rossendorf (HZDR)*, which showcase the potential but also several challenges associated with the measurement concept.