EDDY-CURRENT CONTROL IN THE AGS RAPID-CYCLING BOOSTER ACCELERATOR MAGNETS

The Booster requires highly variable magnet cycles. When B is large, e ddy current induced sextupole, etc., in the dipole vacuum chamber (VC) is large, with a much smaller contribution from magnet ends. Simple p assive coils excited automatically by transformer action cancel the B induced sextupole.1 A self correction coil is not required for the qua drupoles, since B induced aberrations are very small (< 1.0 x 10(-4) a t full aperture). Iron magnetization does not produce dipole or quadru pole magnet multipole aberrations, so these magnets have been effectiv ely made independent of unwanted multipoles for all cycles. However, v ariations in the transfer functions and thus the Booster tune have not been automatically eliminated. Iron magnetization contributions are a lmost matched, but the B induced field retardation in the dipoles VC i s larger than in the quadrupoles. Results of measurements will be pres ented, plus a simple system to overcome the mismatch and make the tune independent of B. Properties of special lattice magnets and their cor rections will also be described.