  Beam stability and halo formation in high-intensity axisymmetric 2D beams in
a uniform focusing channel are analyzed using particle-in-cell simulations. The
tune depression - mismatch space is explored for the uniform (KV) distribution
of the particle transverse-phase-space density, as well as for more realistic
ones (in particular, the water-bag distribution), to determine the stability
limits and halo parameters. The numerical results show an agreement with
predictions of the analytical model for halo formation (R.L. Gluckstern, Phys.
Rev. Letters, 73 (1994) 1247).
