A limiting factor for the performance of high intensity linacs proposed for
applications like heavy ion inertial fusion, production of tritium, transm
utation of waste and spallation source for neutrons and neutrinos is the co
ntrol of beam losses. These occur, e.g., through the formation of a halo ar
ound the core of the beam containing particles which will eventually collid
e with the walls of the accelerator pipe. The sum of the applied focusing f
ields and the intense self-fields produced by the beam charge are nonlinear
near the surface of the beam causing instabilities leading to halo formati
on. Here, we investigate with the help of molecular dynamics computer simul
ations whether hard Coulomb collisions between the beam particles act as an
additional cause for a beam halo. However, for the parameters of the high
intensity linacs presently in discussion the beam particles remain sufficie
ntly weakly correlated and intra beam scattering plays no major role in hal
o formation. (C) 2001 Elsevier Science B.V. All rights reserved.