Monitor for the carbon and oxygen impurities in the ASDEX Upgrade tokamak

A Bragg spectrometer for monitoring impurity radiation of hydrogenlike carbon and oxygen at the tokamak ASDEX Upgrade is presented. The use of fast multistrip proportional counters allows soft x-ray photon counting with count rates above 1 MHz in a simple arrangement. The absolute calibration was performed using a large area x-ray tube with a LiF anode. The concentrations of both impurities are calculated using the coronal model both for ionization and electron impact excitation. The results of the measurements concerning the long term behavior before and after conditioning of the torus walls by boronization as well as the fast plasma processes are presented.