Schottky Noise Signal and Momentum Spread for Laser-Cooled Beams at Relativistic Energies

We present results on laser-cooling of relativistic bunched C3 ion beams at the the Experimental Storage Ring at GSI, Darmstadt. With moderate bunching at a few volts, beams of triply charged carbon ions with a beam energy of 122 MeV per nucleon have been lasercooled to relative longitudinal momentum spreads of about 2 × 10−6 and below at beam currents of the order of several μA. By detuning the bunching frequency relative to the laser frequency, the acceptance range of the laser force can be increased to match the beam momentum spread. Subsequently decreasing the detuning reduces the momentum spread to values below the resolution of the Schottky noise spectrograph. The reduction of the beam momentum spread is accompanied by a drop in the Schottky noise power by seven to eight orders of magnitude until the signal vanishes completely.