I. Rodriguez* , ISIS, Rutherford Appleton Laboratory, STFC, Didcot, UK
Type QX106 singlet magnets are AC defocusing quadrupoles used in the ISIS main synchrotron ring. They have an aperture of 202 mm and a yoke length of 303 mm, so the end effects are significant. The iron poles and the yoke are asymmetric and the coils are driven by a 50Hz, 400 A AC current, biased with a DC current of 665 A. Therefore the yoke has to be laminated, and the laminations are slitted up to a depth of 90 mm on each side to further reduce the eddy current losses. Two 3D models (DC and transient) have been developed using OPERA 3D for different purposes. Both models require the use of an anisotropic BH curve for the yoke, and the transient model also requires an anisotropic conductivity and a prismatic/hexahedral mesh to overcome the limitations of the linear tetrahedral edge elements in OPERA’s vector potential formulation. The quadrupole field quality was originally measured in 1982 with a DC excitation at the biased peak current (1065 A) and those measurements are now compared to both models. The iron losses due to the eddy currents are also presented and compared to the original specifications defined in 1980, as well as an estimation of the eddy currents in the coils.
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