Solid core dipoles and switching power supplies: lower cost light sources?

TL;DR

This paper investigates the use of solid core dipoles powered by switching supplies, demonstrating that eddy currents can significantly reduce ripple effects, potentially lowering costs for light source accelerators.

Contribution

It models eddy current effects in solid steel dipoles to show how switching power supplies can achieve low noise levels suitable for accelerator applications.

Findings

Eddy currents reduce ripple to below 1% of input ripple at relevant frequencies.

Solid core dipoles with switching supplies can meet beam quality requirements.

Cost-effective solutions for light sources are feasible with this approach.

Abstract

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.