Chromatically Corrected Imaging Systems for Charged-Particle Radiography

In proton radiography, imaging with systems consisting of quadrupole magnets is an established technique for viewing the material distribution and composition of objects, either statically or during fast events such as explosions. With the standard magnet configuration, the – I lens, chromatic aberrations generally dominate the image blur. Image resolution can be improved, and largely decoupled from the input-beam parameters, by using a second-order achromat with some additional higher-order aberration correction. The aberration-correction approach is discussed. For a given resolution, such an achromat allows use of much lower-energy imaging particles than a – I lens. Each achromat design can be scaled into many equivalent systems; an 800-MeV proton design and its equivalent 40-MeV electron system are presented. The electron system is useful for imaging thin objects. Magnet errors in the achromats must be tightly controlled to preserve image quality, but not beyond feasibility of present technology. System performance is verified by particle tracking. Configurations alternative to the canonical achromat are discussed.