Ion-optical design for PRIOR

Proton radiography or microscopy is a novel technique for probing the interior of dense objects in dynamic experiments by mono-energetic beams of GeV-energy protons. A special system of magnetic lenses is employed for imaging and aberrations correction. Using this technique, one can measure areal density of a thick sample with sub-percent accuracy. The spatial resolution is a few micrometers over a centimeter-wide field of view, whereas the time resolution is on the nanosecond scale. Recently an international project PRIOR (Proton Microscope for FAIR) [1] was started for developing of a new proton microscopy facility according to the requirements of the HEDgeHOB collaboration experiments at FAIR. The PRIOR microscope will be able to initially be fielded at GSI for testing and commissioning with the same SIS-18 proton beam as later used at FAIR. Its installation at the HHT experimental area of GSI and commissioning in static and dynamic experiments with a 4.5 GeV proton beam from the SIS-18 synchrotron is currently under discussion. The PRIOR magnetic lens system is designed utilizing quadrupole magnets as focusing elements. The most cost effective quadrupole technology for both fabrication and operation costs are permanent magnet quadrupoles (PMQ) constructed from rare earth permanent magnet material (REPM). Having a small aperture, PMQ can reach high field gradients while maintaining high magnetization. PMQ were successfully employed in proton microscopes for 0.8 GeV proton beams at LANL [2] and at ITEP [3]. A prototype of the PRIOR PMQ with a 15 mm aperture and 238 T/m magnetic field gradient has been recently constructed at ITEP. For enlarging the field of view of the imaging optics, 30 mm aperture PMQs are also considered for PRIOR.