Y. Cai

LEGO: a modular accelerator design code

An object-oriented accelerator design code has been designed and implemented in a simple and modular fashion. It contains all major features of its predecessors: TRACY and DESPOT. All physics of single-particle dynamics is implemented based on the Hamiltonian in the local frame of the component. Components can be moved arbitrarily in the three dimensional space. Several symplectic integrators are used to approximate the integration of the Hamiltonian. A differential algebra class is introduced to extract a Taylor map up to arbitrary order. Analysis of optics is done in the same way both for the linear and non-linear case. Currently, the code is used to design and simulate the lattices of the PEP-II. It will also be used for the commissioning.

Simulation of the Beam-Beam Effects in e+e- Storage Rings with a Method of Reducing the Region of Mesh

A highly accurate self-consistent particle code to simulate the beam-beam collision in

Low Energy Ring lattice of the PEP-II asymmetric B-factory

{e}^{+}{e}^{\ensuremath{-}}

New simulation results for the electron-cloud effect at the PEP-II positron ring

storage rings has been developed. It adopts a method of solving the Poisson equation with an open boundary. The method consists of two steps: assigning the potential on a finite boundary using Greens function and then solving the potential inside the boundary with a fast Poisson solver. Since the solution of Poissons equation is unique, our solution is exactly the same as the one obtained by simply using Greens function. The method allows us to select a much smaller region of mesh and therefore increase the resolution of the solver. The better resolution makes more accurate the calculation of the dynamics in the core of the beams. The luminosity simulated with this method agrees quantitatively with the measurement for the PEP-II B Factory ring in the linear and nonlinear beam current regimes, demonstrating its predictive capability in detail.

An X-ray Free Electron Laser Driven by an Ultimate Storage Ring

Developing a lattice that contains a very low beta value at the interaction point (IP) and has adequate dynamic aperture is one of the major challenges in designing the PEP-II asymmetric B-factory. For the Low Energy Ring (LER) we have studied several different chromatic correction schemes since the conceptual design report (CDR). Based on these studies, a hybrid solution with local and semi-local chromatic sextupoles has been selected as the new baseline lattice to replace the local scheme in the CDR. The new design simplifies the interaction region (IR) and reduces the number of sextupoles in the arcs. Arc sextupoles are paired at /spl pi/ phase difference and are not interleaved. In this paper we describe the baseline lattice with the emphasis on the lattice changes made since the CDR.

An orbit and dispersion correction scheme for PEP-II

We present simulation results for the emittance blowup due to the head-tail effect induced by the electron-cloud effect in the low-energy ring at the PEP-II B factory at SLAC.

Swamp plots for dynamic aperture studies of PEP-II lattices

There is a worldwide interest in developing so-called ultimate storage ring (USR) light sources having electron emittances near the X-ray diffraction limit that would provide spectral brightness one or two orders of magnitude higher than present-day, third-generation sources and very large coherent flux in the multi-keV photon energy range [1]. At the same time, there is a growing scientific interest in X-ray FEL sources that can provide a continuous train of evenly spaced, low peak power, coherent photon pulses at repetition rates of above 1 kHz, unlike the bursts of much higher frequency pulses that can be provided by linac-based FELs pulsed with repetition rates of order 100 Hz or less. These CW sources would enable dynamic imaging of materials undergoing transitions in millisecond or less time scales and would open up the development of new non-line spectroscopic techniques that could lead to a better understanding of electronic and nuclear dynamics in materials.

R&D for a Soft X-Ray Free Electron Laser Facility

A scheme of simultaneously correcting the orbits and dispersion has been implemented in a simulation code. And on-line control system for PEP-II. The scheme is based on the eigenvector decomposition method. An important ingredient of the scheme is to choose the optimum eigenvectors that minimize the orbit, dispersion and corrector strength. Simulations indicate this to be a very effective way to control the vertical residual dispersion.

Dynamical Effects due to Fringe Field of the Magnet in Circular Accelerators

With a newly developed algorithm using resonance basis Lie generators and their evaluation with action-angle Poisson bracket maps (nPB tracking), we have been able to perform fast tracking for dynamic aperture studies of PEP-II lattices as well as incorporate lattice nonlinearities in beam-beam studies. We have been able to better understand the relationship between dynamic apertures and the tune shift and resonance coefficients in the generators of the one-turn maps. To obtain swamp plots (dynamic aperture vs. working point) of the PEP-II lattices, we first compute a one-turn resonance basis map for a nominal working point and then perform nPB tracking by switching the working point while holding fixed all other terms in the map. Results have been spot-checked by comparing with element-by-element tracking.

Computational tools and lattice design for the PEP-II B-Factory

R&D for a Soft X-Ray Free Electron Laser Facility A White Paper Report prepared by LBNL and SLAC with contributions from LBNL: David Attwood, John Byrd, John Corlett, Peter Denes, Roger Falcone, Phil Heimann, Wim Leemans, Howard Padmore, Soren Prestemon, Fernando Sannibale, Ross Schlueter, Carl Schroeder, John Staples, Marco Venturini, Tony Warwick, Russell Wells, Russell Wilcox, and Alexander Zholents SLAC: Chris Adolphsen, John Arthur, Uwe Bergmann, Yunhai Cai, Eric Colby, David Dowell, Paul Emma, John Fox, Josef Frisch, John Galayda, Robert Hettel, Zhirong Huang, Nan Phinney, Tom Rabedeau, Tor Raubenheimer, David Reis, John Schmerge, Joachim Stohr, Gennady Stupakov, Bill White, and Dao Xiang Lawrence Berkeley National Laboratory SLAC National Accelerator Laboratory June 2009