BEAM LOSS RATES WITH AN INTERNAL GAS-TARGET IN AN ELECTRON-COOLED STORAGE-RING IMPLICATIONS FOR LUMINOSITY OPTIMIZATION

Measurements have been made in the Cooler ring at the Indiana Universi ty Cyclotron Facility (IUCF) of the mean lifetime of stored and electr on-cooled proton beams in the presence of various target gas species a t two ring locations differing in dispersion. A broad range of beam en ergy T(b), target atomic number Z(t) and thickness x(t) was employed. The loss (removal) Cross section sigma(L) per target atom, extracted f rom the lifetime measurement, exhibits a minimum for small x(t) which is found to scale with (Z(t)/T(b))2. This behavior is expected because forward Coulomb scattering from target nuclei should be the dominant loss mechanism under the conditions of measurement. A marked increase in sigma(L) for larger x(t) is attributed to emittance growth arising from multiple scattering in competition with the transverse cooling ra te. Lattice dispersion at the target increases the contribution to bea m heating by electrons in the target atoms and introduces an additiona l loss mechanism. From the measured sigma(L) and beam lifetime, a time cycle may be selected which gives the optimum time-averaged luminosit y for a given experiment. Scaling Of sigma(L) allows prediction of the optimum luminosity over the full operating regime of the cooling ring .