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| News |
| Collaboration |
| ComPASS Team Helps Diagnose a CEBAF Issue |
| At Jefferson Lab, scientists study quarks, gluons, protons, and neutrons with the Continuous Electron Beam Accelerator Facility (CEBAF) and its three experimental halls. Much like a powerful microscope, CEBAF enables scientists to “see” things a million times smaller than an atom. This unprecedented view is allowing us to gain deeper insight into the particles and forces that form our Universe. |
| When researchers encountered an issue with the beam break up (BBU) in the CEBAF accelerator, they turned to Kwok Ko, Cho Ng, and the Community Petascale Project for Accelerator Science and Simulation (ComPASS) team for assistance. Utilizing the advanced codes developed under the SciDAC program, the ComPASS team was able to accurately model the superconducting cavity configuration installed in Jefferson Lab’s prototype cryomodule and, from external measurements, “reverse engineer” what must have happened during assembly. The BBU issue was tracked and attributed to a particular cavity which had a non-standard preparation history, one that resulted in a mechanical distortion of the shape. The cavity performed well in normal operating mode, but a higher-order mode (HOM) that should have been damped was tilted away from the coupler designed to extract it (figure 4). |
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| ComPASS Team |
| Figure 4.
The electric field pattern of an HOM in the ideal (top) and deformed (bottom) cavities. In the deformed cavity, the field shifts away from the HOM coupler at the left beam-pipe, leading to its high Q value. The calculations were carried out using Omega3P. |
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By using unique and highly accurate algorithms and solvers developed at the SLAC National Accelerator Laboratory, Volkan Akcelik, Zenghai Li, and their colleagues were able to reconstruct the cell-by-cell distortions that must have occurred. They predicted the cavity variance and examination of inspection records corroborated their prediction. Beam-based measurements confirmed the effect of this distortion in the dynamics of the CEBAF Linac. With this understanding Jefferson Lab is now able to develop improved procedures to check future cavities to prevent reoccurrence of this undesirable effect.
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Further Information
https://compass.fnal.gov/
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