Abstract
An approach to fabricating Halbach array undulators using “combs” machined from single magnets is introduced. This technique is especially relevant to the fabrication of short period micro-undulators with period lengths considerably less than the few-centimeter-scale typical of current undulators. Manual, magnet-by-magnet assembly of micro-undulators would require the manipulation and alignment of thousands of magnets smaller than a grain of rice: comb fabrication dramatically increases the size of the basic unit cell of assembly with no increase in undulator period by creating many periods from a single piece, in a single machining modality. Further, as these comb teeth are intrinsically indexed to each other, tolerances are dictated by a single manufacturing step rather than accumulating errors by assembling many tiny magnets relative to each other. Different Halbach geometries, including M ′ = 2 , M ′ = 4 , isosceles triangle, and hybrid, are examined both from a theoretical perspective and with 3D magnetostatic simulations.
Highlights
An idealized Halbach array of permanent magnets, originally described by Klaus Halbach in1980 [1,2] for use in multipole magnets and undulators, consists of regions of permanent magnet with smoothly rotating residual fields
Halbach arrays have been used extensively in beamline magnets including the construction of permanent magnet wigglers and undulators [3,4,5,6] and multipole magnets including dipoles [7] and quadrupoles [8]
Two nonconventional machining processes in particular are well suited to this task, laser machining and wire electrical discharge machining (EDM), and both are through-bulk processes
Summary
An idealized Halbach array of permanent magnets, originally described by Klaus Halbach in1980 [1,2] for use in multipole magnets and undulators, consists of regions of permanent magnet with smoothly rotating residual fields. “weak” side to the array, enhancing the magnetic field on the strong side and attenuating it on the weak side This leads to more efficient use of the available magnetic flux, giving stronger fields than other magnetization configurations. The most common practical implementation of these hybrid arrays to the realization of undulators involves magnets with alternating polarities with their magnetization vectors oriented in the longitudinal direction, interspersed with high-saturation soft ferromagnets. Such undulators are capable of achieving gap fields significantly higher than PPM undulators, for reasons that will be discussed below
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