Halo formation of bunched beams in periodic focusing systems

A very critical design issue for high intensity proton linacs is to keep particle loss below 1 W/m at the high energy end and allow unconstrained hands on maintenance. Particle loss is caused by a small number of particles outside the dense beam core, called the beam halo. Halo formation of bunched beams in a periodic focusing channel is driven by mismatch, high space charge and temperature anisotropy. Unstable particles oscillate in all 3 phase space planes. Mode overlap due to large mismatch amplitudes can lead to a halo much larger than seen in uniform focusing systems. Resonance crossing due to acceleration is a possibility for designing high intensity linacs.