Complex and catastrophic ion beam focusing with a very thin electrostatic square rainbow lens S. Grujović Zdolšek, N. Nešković, I. Telečki and M. Ćosić Eur. Phys. J. Plus, 137 4 (2022) 477 Published online: 18 April 2022 DOI: 10.1140/epjp/s13360-022-02686-8