A MECHANISM OF ANOMALOUS DIFFUSION IN PARTICLE BEAMS

Experimental observation of particle diffusion mechanism in the presen ce of overlapping parametric resonances generated by a time dependent rf phase modulation is analyzed. We find that the regime of fast emitt ance growth is associated with the rapid particle motion along the sep aratrix of a dominant parametric resonance, the slow growth regime is related to particle diffusion in the chaotic sea, and the emittance sa turation occurs when beam particles fill the chaotic region bounded by an invariant torus. Experimental data observed at the Indiana Univers ity Cyclotron Facility (IUCF) Cooler Ring are shown to agree well with the theoretical analysis.