A superconducting coil, about 5.8m in diameter and the same lenth provides a magnetic field of 1.2 Tesla for the H1-detector. The coil is cooled to 4 degrees Kelvin by liquid helium provided from the DESY central refrigeration plant. The coil is surrounded by 2000 tonnes of iron which provides the return yoke for the magnetic field. The iron is highly segmented and filled with detectors in order to record any residual particles that leak out of the back of the main calorimeter (jet tail catcher) and also to measure penetrating particles like muons that pass completely through. The whole H1 detector is surrounded by concrete shielding. The magnetic field in H1 would disturb the circulating beams in HERA and therefore a superconducting compensation coil with opposite field was added.
