Positron-Electron Tandem Ring Accelerator
The Positron-Electron Tandem Ring Accelerator (PETRA) is one of the particle accelerators at DESY in Hamburg, Germany. From 1978 to 1986 it was used to study electron–positron collisions. It was here that the TASSO collaboration found the first direct evidence for gluons in three jet events. The modification called PETRA-II is a source of high-energy synchrotron radiation and also a pre-accelerator for the HERA. Started in 2007, an upgrade has been converting it to PETRA-III, which is a high intensity source for synchrotron radiation.