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.
A METHOD FOR INCORPORATING IMAGE FORCES IN MULTIPARTICLE TRACKING WITH SPACE CHARGE
The simulation of intense beams in synchrotrons or storage rings requires the rapid evaluation of space-charge forces for large macroparticle ensembles. This usually dictates the use of the most economical mesh-based field solvers, such as those based on Fourier-transform methods, which provide essentially a free-space solution for the field in the beam region and do not include image effects due to the vacuum chamber. We describe here a method, recently implemented in the code Accsim[1], for accurately deriving the image-force contributions for arbitrary beam distributions and vacuum chamber geometries, with only a modest increase in computing time. Accsim’s Hybrid-FastMultipole space charge model[2] lends itself particularly well to this approach, which uses harmonic functions and a minimization technique to obtain a parameterized solution for the image potential. The details of the procedure are presented, along with evaluations of its speed and accuracy and some results of validation tracking tests.
Point-to-point and point-to-multipoint communications
A network, such as wired and/or wireless LAN, is configured to have both point-to-point and point-to-multipoint connections. The point-to-multipoint connection(s) is used to communicate information between a plurality of the stations (or modem, or transceivers) in the network, whereas the point-to-point connection(s) are used to communicate information between only 2 stations in the network with the ability to, for example, maximize performance (rate/reach/BER/latency/etc) between those two stations. A master station allocates one or more frequency bands to the various point-to-multipoint and point-to-point connections.