Observation of space-charge effects in the Los Alamos Proton Storage Ring

In recent operation of the Los Alamos Proton Storage Ring (PSR), the vertical and horizontal tunes have been moved closer to the integers ( nu /sub y/=2.12, nu /sub x/=3.17) to enlarge the low-loss working region. In this region, the beam can be significantly affected by space charge. The first observed effects are a nondestructive distortion of the beam profile and vertical growth of beam size sufficient to keep the shifted tunes from crossing the integer, but without large beam loss. At higher intensities, or with tunes closer to the integer, beam blow-up, accompanied by beam losses, can occur. A report is presented on recent observations of this intensity-dependent effect and implications for future PSR operation are discussed. >