  Dense plasma environment affects the electronic structure of ions via
variations of the microscopic electrical fields, also known as plasma
screening. This effect can be either estimated by simplified analytical models,
or by computationally expensive and to date unverified numerical calculations.
We have experimentally quantified plasma screening from the energy shifts of
the bound-bound transitions in matter driven by the x-ray free electron laser
(XFEL). This was enabled by identification of detailed electronic
configurations of the observed K{\alpha}, K\b{eta} and K{\gamma} lines. This
work paves the way for improving plasma screening models including connected
effects like ionization potential depression and continuum lowering, which will
advance the understanding of atomic physics in Warm Dense Matter regime.
