Absolute Calibration of a Ppm-Precise HV Divider for the Electron Cooler of the Ion Storage Ring CRYRING@ESR

The heavy ion storage ring CRYRING at GSI provides a unique possibility to test atomic structure calculations with slow exotic ion beams. In order to cool the ions and thus achieve a low momentum spread of the stored beam, CRYRING features an electron cooler, where the ion beam is superimposed with a mono-energetic electron beam. In high-precision experiments at ion storage rings the velocity of the ions is a critical quantity. For measurements at CRYRING the electron cooler determines the ion velocity and momentum spread of the ions. Consequently, a precise knowledge of the acceleration voltage of the electron beam is essential for the accuracy of the experiments.