Magnetic Field Stability and Current Ripple of Collector Ring Dipole Magnets

The magnetic field stability of the collector ring dipole magnets has been studied with driving current ripple phenomena. The current ripple and corresponding magnetic field variation can be a cause of the beam orbit instability. We investigate the magnetic field variation due to the current ripple in the frequency range of 10 Hz to 10 kHz. The amplitude of magnetic field variation has the exponential decay with respect to the increasing current ripple frequency. This result explains the effect of the secondary magnetic field in the beam chamber. Although the dipole field variation is reduced, the higher odd-number multipoles by eddy current are not compensated. The multipole profiles depend on the beam chamber shape. We present the field stability simulation results including the secondary field harmonics with the vacuum beam chamber geometry.