For absolute soft‐x‐ray line intensity measurements to deduce elemental concentrations and parameters of magnetically confined plasmas large‐area x‐ray sources are developed and investigated. These calibration sources useK,L, andMtransitions in different elements and cover a wide photon energy (and wavelength) range. From the measured absolute line intensities of these sources the quantum efficiency values of numerous elements forK‐,L‐, andM‐line emission per incident electron are deduced. They represent the basis of simple soft‐x‐ray monitors for impurities in fusion plasmas. ©1996 American Institute of Physics.