Double ionization of helium with a convoluted quasi Sturmian approachAlexandr S. Zaytsev, Darya S. Zaytseva, Lorenzo Ugo Ancarani and Sergey A. ZaytsevEur. Phys. J. D, 73 6 (2019) 111DOI: https://doi.org/10.1140/epjd/e2019-90618-x