The Cornell Electron Storage Ring (CESR) is an electron-positron collider at Cornell University in Ithaca, New York, United States. The CLEO and CUSB particle detectors collected data at CESR, and the CHESS facility used the synchrotron radiation to perform a variety of studies.
CESR was built in the already existing tunnel for the 10 GeV synchrotron. It delivered its first collisions in April 1979. The 10 GeV energy turned out to be ideal for the study of B mesons, and CESR would operate near this energy for over twenty years. CESR installed sets of wiggler magnets in the early 2000s to allow operation at lower energies for the CLEO-c project. After the end of particle physics experiments, CESR is now a test facility of damping rings for a future international linear collider.
CESR pioneered several new accelerator techniques, including superconducting radio-frequency cavities and pretzel orbits.