  As a result of improvements in power semiconductors, moderate frequency
switching supplies can now provide the hundreds of amps typically required by
accelerators with zero-to-peak noise in the kHz region ~0.06% in current or
voltage mode. Modeling was undertaken using a finite electromagnetic program to
determine if eddy currents induced in the solid steel of CEBAF magnets and
small supplemental additions would bring the error fields down to the 5ppm
level needed for beam quality. The expected maximum field of the magnet under
consideration is 0.85T and the DC current required to produce that field is
used in the calculations. An additional 0.1% current ripple is added to the DC
current at discrete frequencies 360 Hz, 720 Hz or 7200 Hz. Over the region of
the pole within 0.5% of the central integrated BdL the resulting AC field
changes can be reduced to less than 1% of the 0.1% input ripple for all
frequencies, and a sixth of that at 7200 Hz. Doubling the current, providing
1.5T central field, yielded the same fractional reduction in ripple at the beam
for the cases checked. For light sources with aluminum vacuum vessels and full
energy linac injection, the combination of solid core dipoles and switching
power supplies may result in significant cost savings.
