• J.A. Holmes, S.M. Cousineau, V.V. Danilov
  ORNL, Oak Ridge, Tennessee
• Z. Liu
  IUCF, Bloomington, Indiana

As SNS continues to ramp toward full intensity, we are acquiring a wealth of experimental data. Much effort is being applied to understand the details of the beam accumulation process under a variety of experimental conditions. An important part of this effort is the computational benchmarking of the experimental observations. In order to obtain quantitative agreement between the calculations and the observations, and hence a full understanding of the machine, a great deal of care must be taken to incorporate all the relevant experimental parameters into the calculation. These vary from case to case, depending upon what is being studied. In some of these cases, the benchmarks have been critical in unearthing flaws in the machine and in guiding their mitigation. In this paper we present the results of benchmarks with a variety of experiments, including coupling in beam distributions at low intensities, space charge effects at higher intensities, and a transverse instability driven by the impedance of the ring extraction kickers.

• T.V. Gorlov, A.P. Shishlo
  ORNL, Oak Ridge, Tennessee

The laser assisted hydrogen stripping becomes a widely discussed alternative for the existing stripping foil approach. The simulation tool for this new approach is presented. The created application is implemented in form of extension module to Python ORBIT parallel code that is under development at the SNS. The physical model of the application deals with quantum theory and allows calculating evolution and ionization of hydrogen atoms and ions affected by superposition of electromagnetic and laser fields. The algorithm, structure, benchmark cases, and results of simulations for several future and existing accelerators are discussed.

• B.G. Pine, D.J. Adams, B. Jones, C.M. Warsop, R.E. Williamson
  STFC/RAL/ISIS, Chilton, Didcot, Oxon

The ISIS Facility at the Rutherford Appleton Laboratory in the UK produces intense neutron and muon beams for condensed matter research. It is based on a 50 Hz proton synchrotron which accelerates ~3·10¹³ protons per pulse (ppp) from 70 to 800 MeV, corresponding to beam powers of ~0.2 MW. Studies are under way for major upgrades in the Megawatt regime. Underpinning this programme of operations and upgrades is a study of the high intensity effects that impose limitations on beam power. The behaviour of the beam in the 50 Hz rapid cycling synchrotron (RCS) is largely characterised by high space charge levels and the effects of fast ramping acceleration. High intensity effects are of particular importance as they drive beam loss, but are not fully understood with only limited analytical models available. This paper reviews several methods by which these effects are explored numerically on ISIS, and compares them where possible with experimental or analytical results. In particular we outline development of a new space charge code Set, which is designed to address key issues on ISIS and similar RCS machines.

• S.Y. Xu, S.X. Fang, S. Wang
  IHEP Beijing, Beijing

The China Spallation Neutron Source (CSNS) is now in the design stage. Many simulations have been done for the RCS/CSNS, including the space charge induced emittance growth and beam loss, the combined effects of space charge and magnet errors, the dependence of space charge effects on the lattice structures, etc.

Slides

• E.W. Nissen, B. Erdelyi
  Northern Illinois University, DeKalb, Illinois

This research involves the development of a model of the small circumference (11.5 m) accelerator in which the earth’s field has a strong effect, and in which image charge forces are also included. The code used for this simulation was COSY Infinity 9.0 which uses differential algebras to determine high order map elements, as well as quantities such as chromaticity. COSY also uses Normal Form algorithms to determine the betatron tune and any amplitude dependent tune shifts which may result. The power of COSY is that it can derive the required quantities directly form the map without costly integration and tracking. Thus determining the map for both the default elements of the ring, plus the effects of image charge forces, and the earth’s magnetic field is both non-trivial, and important. This research uses the Baker Campbell Hausdorf method to determine the map of the ring with the external fields included. Furthermore COSY has the ability to directly implement misalignments within the beamline itself allowing for a study of their effects on beam dynamics. The presentation will include both coding development and applications to the University of Maryland Electron Ring.

• M. Xiao, D.E. Johnson
  Fermilab, Batavia

The Recycler is a fixed 8 GeV kinetic energy storage ring using permanent gradient magnets. A phase trombone straight section is used to control the tunes. For ProjectX , the H-particle extracted from the Linac will be striped and painted in the Recycler Ring and then the protons will be extracted into the Main injector. A long drifting space is needed to accommodate the injection chicane with stripping foils. In this paper, the existing FODO lattice in rr10 straight section being converted into doublet will be described. Due to this change, the phase trombone straight section has to be modified to bring the tunes to the nominal working point. On the other hand, a toy lattice of recycler ring is designed to simulate the end-shim effects of each permanent gradient magnet to add the flexibility to handle the tune shift to the lattice during the operation of 1.6·10¹⁴ with KV distribution of the proton beam to give ~0.05 of space charge tune shift . The comparison or the combinations of the two modification ways for the Recycler ring lattice will be presented also in this paper.