Space charge dynamics in high intensity rings

Abstract

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-chargedriven 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.

Instabilities of high-order beam modes driven by space-charge coupling resonances

“…Simulations were carried out with a KV beam for the previous FODO SNS lattice with a working point ͑n x , n y ͒ ͑5.82, 5.77͒ and a space-charge tune shift of about 0.08. We note that in the Appendix we analyze the data based on simulations with the ACCSIM code [1,14]. A detailed comparison of ACCSIM with ORBIT done by Jeon [7] showed that tunes in the vertical direction are slightly less depressed with the ACCSIM code by approximately dn 0.015 compared to the ORBIT code.…”

Parallel Algorithms for Collective Processes in High Intensity Rings

“…where the parameters 3 τ , 4 τ ,a n d comm τ are 3.3E-6, 3.8E-7, and 2.1E-6 sec, respectively. The first term in the formula (2) describes the time spent binning the macroparticles, applying the space charge kick, etc.…”

“…In order to study the dynamics of high intensity rings, a task essential to the SNS project [1], we have developed direct space charge and impedance models in the macro-particle tracking computer code, ORBIT [2,3]. Initially, separate transverse space charge and longitudinal space charge/impedance models were developed, benchmarked, and applied to a number of problems [4,5]. We have now extended the impedance model to include the calculation of forces due to transverse impedances and, because such forces depend on the longitudinal variation of the beam dipole moments, the space charge model has been extended to three dimensions.…”

Space charge induced resonance excitation in high intensity rings

“…Historically, these studies were performed for linac beams, where the peak density of particles is much greater than in rings. The effect of space charge on the synchrotron beam is a more recent concern, and analogous PCM studies are being undertaken for the ring beam environment [7]. In these studies, the particle core model has either been applied to idealized lattice structures and beam parameters, or the effects of the lattice have not been critically examined.…”