Design and measurements of a thin quadrupole magnet for the AGS synchrotron

Abstract Four quadrupoles were installed in four straight sections of the AGS synchrotron to compensate for the effect on the beam optics of two helical magnets also installed in the AGS. The overall length of each quadrupole is less than 30 cm, so it fits in the 62 cm long straight section of the AGS ring. At injection energies, the strength of each quadrupole is set at a high value, and is ramped down to zero during the acceleration cycle, as the effect of the helical magnets on the circulating beam, diminishes by the square of the beam's rigidity. To minimize the eddy currents generated in the iron core of the quadrupole, by the transient magnetic field during the ramp down time, the quadrupoles were laminated. In this paper we describe the process of designing the quadrupole, with three of the most important aspects of the design discussed below. The first was to select the maximum thickness of the iron lamination that does not affect significantly the field quality of the quadrupole during the ramp down time interval, and also reduces to an acceptable level the ohmic losses generated in the iron laminations. The second was to minimize the higher order, 12pole allowed magnetic multipole of the quadrupole. The third was to calculate the ohmic losses in the iron laminations, as a function of both the lamination thickness and the magnetic field strength. The calculated ohmic losses in the iron laminations as a function of time and lamination thickness are consistent with the time evolution of the eddy currents inside the laminations. Simple experimental measurement of the current and voltage across the coil of the magnet as a function of time, qualitatively agrees with the theoretically calculated ohmic losses in the iron laminations.