HALO FORMATION IN SPHEROIDAL BUNCHES WITH SELF-CONSISTENT STATIONARY DISTRIBUTIONS

A new class of self-consistent 6-D phase space station-ary distributions is constructed both analytically and nu-merically. The beam is then mismatched longitudinally and/or transversely, and we explore the beam stability and halo formation for the case of 3-D axisymmetric beam bunches using particle-in-cell simulations. We concentrate on beams with bunch length-to-width ratios varying from 1 to 5, which covers the typical range of the APT linac parameters. We find that the longitudinal halo forms first for comparable longitudinal and transverse mismatches. An interesting coupling phenomenon — a longitudinal or transverse halo is observed even for very small mismatches if the mismatch in the other plane is large — is discovered.