Field measurements of the compensating solenoids in the HERA e-p storage-ring

A measuring device was developed that is capable of determining the field parameters of a solenoid magnet by means of a precision Hall probe. The probe is sensitive to the three orthogonal field components and may be mounted either on a small trolley to run along or on a crank rotating around the axis of the magnet. This way the strength of the magnet as well as the lateral position of the magnetic axis with respect to the mechanical axis of the magnet may be determined. The measured value for the strength of the magnet meets the design value, while the position of the axis deviates considerably. If a second measurement, which is still to be done, confirms these findings, the construction and the alignment of the superconducting coil inside the cryostat will have to undergo a close examination. >