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abstract:
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Advanced high-brightness beam applicaitons
such as inverse-Compton scattering (ICS) depend on achieving
of ultra-small spot sizes in high current beams. Modern injectors
and compressors enable the production of high-brightness beams
having needed short bunch lengths and small emittances. Along with
these beam properties comes the need to produce tighter foci,
using stronger, shorter focal length optics. An approach to
creating such strong focusing-systems using high field, small-bore
permanent-magnet quadrupoles (PMQs) is reported here. A final
focus system employing three PMQs, each composed of 16 neodymium
iron boride sectors in a Halbach geometry has been installed in
the PLEIADES ICS experiment. The field gradient in these PMQs is
560 T/m, the highest ever reported in a magnetic optics system. As
the magnets are of a fixed field-strength, the focusing system is
tuned by adjusting the position of the three magnets along the
beamline axis, in analogy to familiar camera optics. This paper
discusses the details of the focusing system, simulation, design,
fabrication and experimental procedure in creating ultra-small
beams at PLEIADES.
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