Multi-scale modeling for beam-beam depolarization

To elucidate the mysterious origins of nuclear spin, the Nuclear Science Advisory Committee (NSAC) has identified the science of electron-ion colliders, and specifically a proposed polarized electron-ion collider, as “absolutely central to U.S. science”. Such machines, estimated to cost as much as $500M–$1B, will require polarized particle beams; and high polarization improves experimental efficiency. To reduce the risk associated with building these machines, and to ensure the desired high polarization, scientists need accurate simulations of the spin dynamics. While codes exist for simulating spin dynamics in particle accelerators, none include a realistic, self-consistent treatment of the beam-beam interaction. In the context of electron-ion colliders, this interaction can have a profound effect on the electron beam polarization. It is therefore essential that scientists develop a realistic understanding of how the beam-beam interaction will affect machine performance. Statement of how this problem is being addressed We will couple together the capabilities of two separate codes: one capable of performing fast spin-orbit tracking in storage rings, and another capable of self-consistent 3D simulations of the beam-beam interaction. The latter code will be extended so that it also tracks the spin degrees of freedom for particles in a simulation. We will couple both inputs and outputs of these two codes, so that scientists can study in detail the effect of multi-pass beam-beam collisions on the polarisation of both beams in a given design for an electron-ion collider. What is to be done in the Phase I During the Phase I project, we will take a code that is capable of self-consistent 3D beam-beam simulations and extend it to include the spin degrees of freedom and also implement spin integration. We will identify how best to connect the input and output streams of this code and a traditional spin-orbit tracking code so that scientists can perform multi-pass simulations. And we will implement a simple version of a particle-field updater as a prototype for simulating laser-gain media. Commercial applications and other benefits The proposed software development will directly benefit scientists working to design the electron-ion collider required for fundamental advances in experimental nuclear physics. In addition, the work done to include spin integration in the beam-beam simulations can be further extended so as to simulate the dynamics of laser gain media. This new software capability will significantly extend the range of lasers that can be simulated, and it will have particular relevance to the simulation of both high-power and short-pulse-length lasers.