Quantum Electrodynamics in Strong Electromagnetic Fields: Substate Resolved K$\alpha$ Transition Energies in Helium-like Uranium

Philip Pfäfflein, Günter Weber, Steffen Allgeier +34

Using novel metallic magnetic calorimeter detectors at the CRYRING@ESR, we recorded X-ray spectra of stored and electron cooled helium-like uranium (U${}^{90+}$) with an unmatched sp…