Superconducting Compensating Solenoids for the Cello Detector Experiment at Petra

Abstract

One of the main components of the detector experiment CELLO in the e⁺e^- storage ring PETRA at DESY/Hamburg is the superconducting magnet system. The magnets have been developed as a joint project by CEN/Saclay and Kernforschungszentrum Karlsruhe. CEN has built the thin-walled main solenoid with a length of 3.5 m and a winding diameter of 1.7 m creating a magnetic field of 1.5 T in the center [¹]. Two magnetically identical solenoids, located symmetrical to the main coil, must be positioned with a magnetic field opposite to the central field to cancel the integral field effect on the orbiting particle beams. This compensating solenoid system, including its supporting cryogenic system, has been designed and constructed by the Kernforschungszentrum Karlsruhe. The main coil was constructed with a wall thickness of ≤ λ/2 (equivalent to 45 mm of aluminum); this requirement was imposed by the radiation length λ of the generated particles. The compensating coils, on the other hand, were designed and built by conventional techniques for superconducting magnets. The solenoids within their cryostats are to be mounted in movable iron yoke doors surrounded by muon chambers and a liquid argon end cap calorimeter as shown in Fig. 1. The outer geometry and the required warm bore parameters determine the dimensions of the cryostats, i.e., a length of 1.10 m and an outer and inner diameter of the horizontal part of 0.8 and 0.4 m, respectively.