Electron cooling of D- at the ASTRID storage ring

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 similar to 4 x 10(-4) (FWHM) to similar to 7 x 10(-5) (FWHM) at a current of similar to 0.1 mu A. 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. (C) 2000 Elsevier Science B.V. All rights reserved.