Absolute calibration of an X-ray spectrometer on the NIST Electron-Beam Ion Trap: Control, design and systematics

The course of Electron-Beam Ion Trap (EBIT) experiments depends more and more on precision measurement. To design and test a system of absolute spectroscopy to 10-20 parts per million for such a source is a challenging task. Other design criteria include good efficiency in the 3-10keV energy range, ability to focus a line source and high vacuum compatibility. Some difficulties are discussed. The use of a non-scanning Johann focusing spectrometer and its consequent calibration is discussed The spectrometer has been used in a series of experiments on the NIST EBIT. The detector location is shown (both experimentally and by modelling) to provide a major systematic contribution, which can however be controlled to a suitable tolerance. Future directions are indicated.