With this work we start a project calculating the QED contribution of order alpha(7)m to the 2(3)P-2(3)S transition energy in helium, aiming for an accurate determination of the nuclear charge radius r(E) from measurements of the corresponding transition frequency. Together with the complementary determination of r(E) from muonic helium, this project will provide a stringent test of universality of electromagnetic interactions of leptons in the Standard Model.
We report a calculation of the relativistic corrections to the Bethe logarithm for the 2(3)S and 2(3)P states, which is the most numerically demanding part of the project.