Abstract
We report macroparticle simulations for comparison with measured results from a proton beam halo experiment in a 52-quadrupole periodic-focusing channel. An important issue is that the input phase-space distribution is not experimentally known. Three different initial distributions with different shapes predict different beam profiles in the transport system. Simulations have been fairly successful in reproducing the core of the measured matched-beam profiles and the trend of emittance growth as a function of the mismatch factor, but underestimate the growth rate of halo and emittance for mismatched beams. In this study, we find that knowledge of the Courant-Snyder parameters and emittances of the input beam is not sufficient for reliable prediction of the halo. Input distributions with greater population in the tails produce larger rates of emittance growth, a result that is qualitatively consistent with the particle-core model of halo formation in mismatched beams.
Highlights
The macroparticle simulation method is widely used in modern accelerator design and beam physics studies [1,2,3,4,5]
The Low-Energy Demonstration Accelerator (LEDA) facility consists of a 75-keV dc injector, a low-energy beam-transport (LEBT) system, and a radio frequency quadrupole (RFQ), which accelerates the proton beam to 6.7 MeV
We find that the emittance-growth rate from simulations increases as we progress from the Waterbag to Gaussian to LEBT/RFQ, i.e., with increasing halo population in the initial distribution
Summary
The macroparticle simulation method is widely used in modern accelerator design and beam physics studies [1,2,3,4,5]. The method provides a quantitative model of the time evolution of charged-particle bunches in accelerators It includes the boundary conditions, the physics associated with external focusing and acceleration, and space-charge forces from intraparticle Coulomb interactions within the bunch. To ensure that macroparticle simulation codes include the most important physics effects, comparisons with experimental measurements are necessary. Such comparisons can test the assumptions and approximations used in the codes. We present comparisons of simulations using the code IMPACT [4] with experimental measurements of the beam profiles including beam halo in a highcurrent proton beam. The present paper focuses instead on a simulation study of beam halo formation in the new 52quadrupole lattice.
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