A hybrid fast-multipole technique for space-charge tracking with halos
The simulation of injection and accumulation of intense proton beams in synchrotrons and accumulator rings requires a flexible and robust treatment of space-charge effects. In particular, the simulation must be able to correctly incorporate the large-amplitude beam halo which is known to arise from a variety of mechanisms. This paper describes a technique for the efficient and accurate evaluation of transverse space-charge forces in a simulated beam that may include halo particles at arbitrarily large amplitudes. The technique uses the Fast Multipole Method (FMM), together with some elements of Particle-In-Cell (PIC) methods, to evaluate the space-charge field at the location of each macroparticle. Timing comparisons show that when a large-amplitude halo is present this hybrid technique is significantly faster than plain FMM and also offers performance advantages over PIC/FFT field calculations with equivalent spatial resolution. The hybrid FMM method has been implemented and tested in the multiparticle tracking and simulation code ACCSIM and some initial results are presented.
Modeling of space-charge phenomena in multi-turn tracking
Although many space-charge simulations have been developed for linacs, beamlines, and idealized rings, there are relatively few simulation codes applicable to multi-turn tracking with space charge in a realistic synchrotron or accumulator/storage ring lattice. Recently the program ACCSTM, used for accumulator-ring injection studies anti other applications, has been upgraded with improved transverse space charge models: one using a conventional multiple-Fourier-transform (MFT) method and another using a new hybrid fast-multipole (HFM) algorithm. After an overview of their implementation in the ACCSTM code, we present tests and observations of how well various space-charge phenomena can be be produced by the HFM models.
Improvement of RHIC warm beam vacuum for high intensity operation
With increasing ion beam intensity during recent RHIC operations, pressure rises of several decades were observed at a few warm vacuum sections. Improvement of the warm sections has been carried out in last year's shutdown. Extensive in-situ bakes, additional UHV pumping, electron detectors and beam tube solenoids have been implemented. Vacuum monitoring and interlock were enhanced to reduce premature beam aborts. The effectiveness of these measures in reducing the beam induced pressure bumps and in increasing the vacuum system reliability are discussed and summarized.