Magnetic Imaging Lenses for the Advanced Hydrodynamic Facility

摘要

In proton radiography, transmission radiographs of dynamic test objects are madeby illuminating the test object with a proton beam from a synchrotrons. The energy of the Advanced Hydrodynamic Facility (AHF) synchrotrons is 50 GeV. Negative images are formed as denser parts of the test object attenuate the incident beam by nuclear scattering of protons out of the beam more than less-dense parts. However, in addition to the nuclear scattering, smaller-angle multiple Coulomb scattering (MCS) of the protons also occurs in the test object, and introduces a spread in the angles of the protons that are not nuclear-scattered. In proton radiography, this blurring effect is almost eliminated by placing the detector at the focal plane of a point-to-point magnetic quadruple lens system. A second lens and detector system may be placed downstream of the first system. A third identity lens (the monitor lens) and detector are placed in front of the test object to record the incident beam intensity profile. Because the detectors are thin, a given proton passes through all of the detectors and is detected in all of them with almost unit probability. An additional large-bore quadruple lens element is placed upstream of the monitor lens and test object to prepare the illuminating beam. In a single three-lens beamline, a total of 13 largebore quadruples is required. In AHF, up to 12 converging and crossing beamlines will be used to make simultaneous images of me test object over a 180-deg. range of view angles. Improved magnetic-optics performance and larger fields of view can be achieved by use of superconducting quadruple magnets, which can produce higher pole-tip fields and gradients than conventional quadruples. In the paper, the design requirements and operating conditions for the quadruples and various approaches to their design are described. Conceptual designs for superconducting quadruples of two sizes, based on a NbTi cable-in-channel conductor, are briefly described.