Collaborative effort helps optimize cavities in accelerators

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Diachin’s ITAPS group is largely focused on improving mesh generation – a method to digitally divide the regions of a system being modeled into a grid – and Adaptive Mesh Refinement (AMR), a technique to focus the grid on regions of most interest to researchers or on regions where there’s the most activity.  It’s like focusing a camera on the subject while the less important background is left fuzzy.

Diachin says her ITAPS group is “about creating the next generation of advanced mesh generation technologies – getting very high quality meshes, and inserting them into application codes” – including one for accelerator cell design.

“We work with a number of different application teams, but probably the most prominent has been the accelerator design team at the Stanford Linear Accelerator Center,” Diachin says.  Besides Stanford, researchers from Rensselear Polytechnic Institute and DOE’s Sandia and Argonne national laboratories are collaborating with Diachin’s group on the project.

Stanford “has been quite successful on the computational end of modeling cavities,” says Tim Tautges, a computational scientist affiliated with Argonne who’s generating some of the tools used for meshes.

The goal was to increase PEP-II’s “beam luminosity” – the number of particles that go through the accelerator successfully.  That’s important because “The more luminosity, the higher the probability of getting the low-probability interactions physicists are looking for, which is the name of the game,” Tautges says.

Reducing The Wake

Increasing beam luminosity largely depends on minimizing the wake fields generated by packets of electrons as they speed through accelerator cavities like that of PEP-II.  Wake fields – electromagnetic waves – are similar to the wake a speeding boat creates, making things rough for the boats that follow.  Electrons have the same problem as they cross the wake fields of electron packets that precede them.

“If too many bunches of particles get sufficiently knocked off their path, they get accelerated into the wall of the cavity, and that’s very bad,” Tautges says.  “That will heat the cavity up and shut the whole thing down.”

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