Positron–Electron Tandem Ring Accelerator
The Positron–Electron Tandem Ring Accelerator (PETRA) is one of the particle accelerators at the German national laboratory DESY in Hamburg, Germany. At the time of its construction, it was the biggest storage ring of its kind and still is DESY's second largest synchrotron after HERA. PETRA's original purpose was research in elementary particle physics. From 1978 to 1986, it was used to study electron–positron collisions with the four experiments JADE, MARK-J, PLUTO and TASSO. The discovery of the gluon, the carrier particle of the strong nuclear force, by the TASSO collaboration in 1979 is counted as one of the biggest successes. PETRA was able to accelerate electrons and positrons to 19 GeV. Research at PETRA led to an intensified international use of the facilities at DESY. Scientists from China, France, Israel, the Netherlands, Norway, the United Kingdom and the USA participated in the first experiments at PETRA alongside many German colleagues. PETRA II In 1990, the facility was taken into operation again under the name PETRA II as a pre-accelerator for protons and electrons/positrons for the new particle accelerator HERA. In March 1995, PETRA II was equipped with undulators to create greater amounts of synchrotron radiation with higher energies, especially