Ingo Hofmann, (GSI Darmstadt, Planckstrasse 1, 64291 Darmstadt, Germany), Ji Qiang, Robert D. Ryne (Los Alamos National Laboratory, Los Alamos, NM 87545)
The question of energy equipartition in space-charge dominated bunched beams is frequently discussed in high-current linac design papers by using quite general terms and concepts borrowed from thermodynamics or nonlinear mechanics. One of the possible conclusions that non-equipartitioned beams should be generally avoided seems premature as long as the underlying physics is not made clear. In this paper we present results of a systematic simulation study of non-equipartitioned bunches in 3D (with constant focusing and no acceleration) and suggest that single-particle resonance as well as coherent instability (also tied to certain resonance conditions) are possible candidates for equipartitioning. Results are summarized on stability charts for a given emittance ratio. They indicate wide regions around the energy equipartition line, where unequipartitioned bunches are stable in spite of significant tune depression. In the unstable regions equipartition is approached, but in general the instability levels off before complete equipartitioning.
Comments or Questions to