Electron cooling of D − at the ASTRID storage ring

Abstract

A report of recent results on electron cooling of D − at an energy of 1.6 MeV in the ASTRID storage ring is given. The longitudinal velocity spread has been reduced from ∼4×10 −4 (FWHM) to ∼7×10 −5 (FWHM) at a current of ∼0.1 μA. A drift in the mean velocity of the cooled beam has been reduced by application of a small RF signal on four sets of plates in the cooler. Initially, the velocity spread is found to decrease with ion current, indicating equilibrium between cooling and intra-beam scattering, whereas at later times (lower current) the velocity spread becomes constant, indicating equilibrium with the electron beam. To diagnose cooling, a simple system allowing to follow the frequency width and position of a Schottky harmonic on a sub-second time-scale, has been developed. The system uses a standard data acquisition card to digitize a down-mixed Schottky-signal and a FFT routine in Labview on a standard PC. The electron-cooled ion-beam is used for high-resolution vacuum ultra-violent spectroscopy of H − and D − in the region near the H( n=2) threshold. The velocity spread of the ion beam can be directly extracted from these experiments.