Hadron Elektron Ring Anlage

HERA (German: Hadron-Elektron-Ringanlage, English: Hadron-Electron Ring Accelerator) was a particle accelerator at DESY in Hamburg. It began operating in 1992. At HERA, electrons or positrons were collided with protons at a center of mass energy of 318 GeV. It was the only lepton-proton collider in the world while operating. Also, it was on the energy frontier in certain regions of the kinematic range. HERA was closed down on 30 June 2007.

The HERA tunnel is located under the DESY site and the nearby Volkspark around 15 to 30 m underground and has a circumference of 6.3 km. Leptons and protons were stored in two independent storage rings on top of each other inside this tunnel. There are four interaction regions, which were used by the experiments H1, ZEUS, HERMES and HERA-B. All these experiments were particle detectors.

Leptons (electrons or positrons) were pre-accelerated to 450 MeV in the linear accelerator LINAC-II. From there they were injected into the storage ring DESY-II and accelerated further to 7.5 GeV before their transfer into PETRA, where they were accelerated to 14 GeV. Finally they were injected into their storage ring in the HERA tunnel and reached a final energy of 27.5 GeV. This storage ring was equipped with warm (non-superconducting) magnets keeping the leptons on their circular track by a magnetic field of 0.17 Tesla.

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