HERA: a supermicroscope for investigating the structure of the proton

HERA, a high energy particle collider at the Deutsches Elektronensychrotron DESY in Hamburg, allows investigation of the structure of the proton with a spatial resolution of 10(-16) cm corresponding to about 1/1000 of its diameter. This view deep into the inner properties of matter is obtained from the scattering of high-energy electrons or positrons from high-energy protons. With its 6.3 km circumference, HERA can be regarded as a gigantic electron microscope. The high energies available at HERA allow a wealth of further studies on the properties of elementary particles and their interactions. After a brief review of earlier experiments, the article describes the concept of HERA and the detectors H1 and ZEUS, with which the scattering events are analyzed, as well, as some of the physics results.