Speaker
Description
A permanent magnet quadrupole (PMQ) that generates its magnetic field without an external power supply and allows the gradient to be varied mechanically was designed. The two-dimensional pole shape was obtained using Non-dominated Sorting Genetic Algorithm II (NSGA-II) with objective functions of $1/|B_2|$ and $|B_6/B_2|$, and an end-edge chamfer angle was selected to minimize the integrated harmonic content. This geometry was extended to a three-dimensional model that accounted for a 2~mm longitudinal pole extension at each end, introduced to fabricate a clamping structure for the poles to the aluminum end plates. Although the earlier study defined the fundamental magnetic design, it did not include the 2 mm extrusion required for the mechanical support structures. The structural changes made to incorporate these supports modified the fringe-field distribution, making an additional optimization necessary to restore the correct longitudinal integrated field. Accordingly, a parametric sweep of the chamfer angle was performed over the machinable range, and the angle was re-selected to minimize the integrated harmonic content within the strength and flat-field constraints. The outcome meets the field quality requirements, with allowed multipole components remaining well below the $5\times10^{-4}$ limit and forbidden components below $10^{-5}$, and achieves a field uniformity of 0.1\,\% at $r_{\mathrm{ref}} = 3$~mm.
Funding Agency
This work was supported in part by the Basic Science Research Program through the National Research Foundation of Korea (NRF) through the Ministry of Education under Grant RS-2023-00247042
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