Final test results for the SNS ring dipoles

To meet the performance parameters of the Spallation Neutron Source (SNS) for high beam intensity with low losses, the compact accumulation ring will contain 32 sector dipoles with 1.44 m effective length and a large aperture, 170 mm. The magnets are built from potted coils and machined pieces of solid iron. When first assembled, the dipoles met the requirements for field uniformity but the rms variation of the integral transfer function (ITF) was much larger than design at both fields of interest, 1.11 T·m and 1.33 T·m, corresponding to proton energies of 1.0 GeV and 1.3 GeV respectively. Based on initial measurements, shims have been added to the return legs or poles, as appropriate, in order to bring the rms variation of the 1.0 GeV ITF to the specification, 0.01%. The value of the ITF rms variation at 1.3 GeV for the shimmed magnets is 0.033%. Sorting the magnets has significantly reduced the load on the correctors due to this ITF variation.