Hydrogen pellet targets for circulating particle beams

A novel internal-target system producing a stream of frozen hydrogen microspheres (pellets) has been installed at the CELSIUS ion storage ring. From test experiments in which the pellet stream crosses the beam of stored protons and deuterons it is concluded that an optimal target thickness of 5 × 1015 atoms/cm2 seen by the beams will give acceptable half-lives of the circulating beams, a few minutes at energies around 1 GeV, as well as acceptable vacuum conditions, about 10−6 mbar, in the scattering chamber. The system is intended for use in high-luminosity experiments with a close to 4 π detector configuration.