Eddy field measurement by using search coils for bending magnet

In order to estimate a field disturbance of a guiding field of a synchrotron due to an eddy current, magnetic fields in a bending magnet have been measured. The magnet was excited by a sinusoidal current with a repetition of 30 Hz. Two search coils were used in the measurements. One is a reference coil and the other is a measurement coil. An imaginary part of an eddy field was derived from the phase difference between two coil signals. The results were compared with a simple two-dimensional model.