Time dependence and temperature stability of the permanent magnets for the Fermilab antiproton recycler ring

The Fermilab Recycler Ring, part of the Main Injector upgrade, is an 8 GeV storage ring consisting of 362 gradient magnets, 109 quadrupoles, 8 mirror magnets, and 5 Lambertsons. The field is driven by strontium ferrite permanent magnets and shaped by precision pole pieces. Temperature dependence of the ferrite is compensated by the use of Ni (30%) Fe (70%) alloy operating near its Curie point. Temperature stability is held to within 0.004%/spl deg/C rms. over the operating range of 25 to 35 C. Tighter stability requirements (0.001%/spl deg/C) for the high beta quadrupoles are met by active thermal control using heating blankets. Longitudinal uniformity is obtained by distribution of the compensator and ferrite throughout the magnet. Field strength in the magnets are adjusted to be within 0.05% of the design field. The higher harmonics contribute less than 0.01% of the primary field measured at a radius of 25.4 mm. For the gradient magnets custom end shims are made to adjust the harmonics; the field is adjusted by adding or subtracting ferrite. The loss of magnetization is logarithmic in time with a /spl Delta/(M/sub 2//M/sub 1/)=9.0/spl times/10/sup -4/ *log (t/sub 2//t/sub 1/), corresponding to a 0.35% loss of field over the expected operating life of 20 years.