Initial tests of planar permanent magnet (PM) quadrupoles with improved high-quality field apertures

In recent years studies have been undertaken on a new class of multipoles consisting of cuboid planar permanent magnet (PM) pieces arranged in bi-planar arrays of 2-fold rotational symmetry. The bi-planarity, while geometrically allowing for the development of miniaturized machine field lattices and long short-period insertion devices with fully open horizontal apertures, also generates high levels of harmonics of the fundamental multipole order in the vicinity of the axis. To circumvent this effect, an algorithm for economically removing these higher harmonics has been recently proposed and quadrupoles based on this approach have been designed at the Stanford Synchrotron Radiation Laboratory (SSRL) and fabricated out of NdFe/B. In this paper we report on initial field measurements of these improved structures carried out at the Magnetic Measurements Laboratory at SLAC