Time-Domain Algorithm for CSR Simulation in LCLS and LCLS-II

Alexander Novokhatski 02/24/2011 revised on 05/20/2011

LCLS Efforts proposal

“Time-domain algorithm for CSR simulation in LCLS and LCLS-II”

Description of Project

This study will focus on the development and application of new methods for modeling electromagnetic fields of charged particles on the very short timescales. These methods will be applied to nonlinear dynamical systems in environments ranging from uniform motion to radiation without restrictions on the acceleration or velocity. The study is very important not only for existing projects, but for future concepts of particle accelerators and ultrafast coherent light sources, where high peak currents and very short bunches are envisioned, which is relevant to most high-brightness beam applications.

The method is based on an implicit scheme of solving the electromagnetic equations. This algorithm is free of frequency dispersion which means that all propagating waves will have their natural phase velocity, completely independent of simulation parameters like mesh size or time step. Other known methods, usually explicit, have “mesh driven” dispersion and because of this they need a much smaller mesh size which slows down calculations and can sometimes cause unstable solutions. An implicit scheme is a self-consistent method that allows us to calculate much shorter bunches. Based on a new algorithm we will develop a powerful code in the future. Existing and future concepts of particle accelerators and ultrafast coherent light sources will benefit from this comprehensive modeling of coherent synchrotron radiation (CSR).

A dispersion-free treatment of the wake fields of short bunches will be directly incorporated into a general algorithm for solving the full set of Maxwell equations. This new capability will allow us to simulate the ultrafast fields in an accelerator vacuum chamber. Naturally all shielded effects due to the metal walls will be included. We will further extend this methodology to more complicated vacuum chambers, thus providing the capability to simulate radiation from different sources including transition radiation. The method will open up the possibility of analyzing nonlinear beam dynamics due to the reaction of the radiation fields. This reaction will be included in the beam simulation. We will also use this new approach to develop improved pictures of the coherent radiation field dynamics. Finally, we will explore new methods to carry forward the simulations rapidly and effectively.

This project may also enable new technologies for understanding and measuring the beam structure of these ultra short bunches with unprecedented spatial and temporal precision. Furthermore, a detailed understanding of the coherent processes will be critical in order to provide maximal scientific output from ultrafast X-ray sources such as LCLS. More importantly, it will be possible to begin developing a detailed understanding of the role of radiation in the formation of the bunch in the bunch compressors. Along with the developing of the algorithm we will design a primary work code for testing the limits of the method.

The implicit scheme in combination with a moving mesh will provide an unlimited simulation region of the beam-field interaction. This is very important for bunch compressor simulations at higher beam energies, where the bunch length is a micron, but the distance between bends is tens of meters.

Anticipated Outcomes

Development and testing of the algorithm for coherent radiation. Developing the primary work code.

Self-consistent simulation ns of the field dynamics in the LCLS bunch compressor BC1. Compare results with the LCLS measurements and “Elegant” simulations.

Results will be presented at the conferences and in publication in journals.