Search Results (3 total)

Transverse beam profiles are observed to broaden with increasing intensity in the Proton Storage Ring at the Los Alamos Neutron Scattering Center. Measured profiles are simulated with an H^- injection model that includes a 2D particle-in-cell space charge calculation. Inclusion of space charge effects in the simulation improves the agreement between the experimentally observed profiles and the calculated profiles. The comparisons are made for a range of injected intensities.

Numerical calculations for the Spallation Neutron Source accumulator ring indicate that lattice resonances excited by the space-charge potential can increase a mismatch significantly by deforming the beam distribution in phase space. Hence increased mismatch leads to enhanced envelope oscillations that are driving the 2:1 parametric resonance leading to halo formation, even for initially matched beams. We have observed this behavior for the 2ν_x-2ν_y=0 resonance and for the 4ν_y=23 resonance. This mechanism for halo formation peculiar to rings through resonance driven mismatch is very sensitive to the tunes, which emphasizes the importance of a careful choice of operating point in tune space.

Uncontrolled beam losses due to space-charge-induced halo generation are a concern in high intensity rings, which are characterized by high beam intensities and low uncontrolled beam loss requirements. It is therefore important to investigate the dynamics of space charge in high intensity rings. We report here the results of extensive calculations using a particle-tracking approach with a self-consistent particle-in-cell model and alternatively with a particle core model. We find that the inclusion of space charge forces provides agreement between calculated and experimentally observed beam profile shapes in the high intensity proton storage ring. We also confirm computationally the extension to rings of the accepted dynamics of halo generation with rms beam mismatch exciting the parametric resonance. In addition, we propose a new two-stage mechanism for halo production in rings in which space-charge-driven lattice resonances generate beam mismatch that excites the parametric resonance. Because of its dependence on lattice resonances, this mechanism is peculiar to rings and is capable of generating halo even from initially matched beams. It is also very sensitive to the operating point in tune space, as we show in the results of a vertical tune scan simulating injection into the Spallation Neutron Source accumulator ring. Our results extend and enhance the understanding of fundamental space charge physics, which has been developed for linear accelerators, to rings.