Status of the R&D activities to the design of an ITER core CXRS diagnostic system

•The CXRS diagnostic for the core plasma of ITER will provide observation of the dedicated diagnostic beam (DNB) over a wide radial range, roughly r/a=0.7 to 0.•A high performance (étendue×transmission, dynamic range) is expected for the port plug system since the beam attenuation is large and the background light omnipresent.•The design is particularly challenging in view of the ITER environment, especially with respect to the first mirror which faces the plasma.•The current status of development is presented by detailing several sub-systems before a four years design phase under an FPA between F4E and the ITER core CXRS Consortium (IC3).