Absolute measurements and simulations of x-ray line energies of highly charged ions with a double-crystal spectrometer

We present a recently constructed double-crystal spectrometer with the purpose of measuring line energies of inner-shell transitions in highly charged ions. Due to its geometrical features, this spectrometer enables absolute measurements of energies with an unprecedented accuracy. We have also developed an ab initio simulation code that allows us to obtain accurate line profiles and estimate geometric and diffraction profile uncertainties. We show the first proof-of-principle measurements on highly charged ions done with this spectrometer. In particular, we present the recent measurement of the M1 transition in He-like Ar with an accuracy of 2.5 ppm and compare it with results of quantum electro dynamic theory.