HIREFS stands for High Resolution Erect Field Spectrometer. It is a grating X-ray spectrometer which allows to analyze CCD response in low energy band (roughly from 250 eV up to 2.5 keV). It consists of a high volatge (5 kVolts) X-ray source (Manson source), a spectrometer chamber with X-ray mirrors and a grating, and a detector chamber. An X-ray beam, generated by the Manson source, passes through an entrance slit of the spectrometer, is focused by the mirrors and then gets dispersed by the reflection grating. The dispersed beam is detected by the CCD, installed in the focal plane of the spectrometer. As a result, different rows of the CCD are illuminated by the X-rays of different wavelength. This allows to extract information on how do CCD parameters, such as energy resolution, response function, and so on, change with the X-ray energy.
Some important results of the CCD characterization with HIREFS can be found in ACIS memos #69 (gyp) (this memo also has an Appendix describing HIREFS itself and procedures, required to start it and shut it down) and #91 (gyp) . There is also HIREFS Operation Procedures .