David B. Barlow

Design and operation of a proton microscope for radiography at 800 MeV

A high-magnification high-resolution option is desirable for the study of small-scale dynamic experiments at the LANSCE 800-MeV Proton Radiography Facility. Magnification is achievable by either repowering the existing imaging-lens quadrupoles, using new high-gradient quadrupoles, or some hybrid combination of the two. The large and complex parameter space of magnetic optics solutions was studied extensively with the 3rd order optics code MARYLIE. Some of the hybrid solutions achieve magnifications up to 150, but at the price of high chromatic aberrations. In the end, a design using only new high-gradient permanent-magnet quadrupoles was selected and built at the design parameters that minimized chromatic aberration per unit magnification. The design has a moderate magnification of 7.1 and 15.8 at the two existing image stations. First-beam commissioning results exceeded expectations. Image contrast is produced by multiple Coulomb scattering in the thin objects. Early experimental objectives are to optimize this contrast by collimator design and by adjusting the correlation in the illuminating beam, as well as to characterize the (quite high) resolution limits of the system.

Compact high-field superconducting quadrupole magnet with holmium poles☆

Abstract A compact high-field superconducting quadrupole magnet was designed and built with poles made of the rare-earth metal holmium. The magnet is intended for use in superconducting coupled-cavity linear accelerators where compact high-field quadrupoles are needed, but where the use of permanent magnets is ruled out because of trapped-flux losses. The magnet has a clear bore diameter of 1.8 cm. outside diameter of 11 cm. length of 11 cm. and pole tip length of 6 cm. The effect of using holmium. a material with a higher saturation field than iron, was investigated by replacing poles ofde of iron with identical poles made of holmium. The magnet was operated at a temperature of 4.2 K and reached a peak quadrupole field gradient of 355 T/m. a 10% increase over the same magnet with iron poles. This increase in performance is consistent with calculations based on B – H curves that were measured for holmium at 4.2 K.

Variable-field permanent-magnet dipole

A new concept for a variable-field permanent-magnet dipole (VFPMD) has been designed, fabricated, and tested. The VFPMD is a C-shaped sector magnet with iron poles separated by a large block of magnet material (SmCo). The central field can be continuously varied from 0.07 T to 0.3 T by moving an iron shunt closer or further away from the back of the magnet. The shunt is specially shaped to make the dependence of the dipole field on the shunt position as linear as possible. The dipole has a 2.8 cm-high by 8 cm-wide aperture with /spl sim/10 cm-long poles. >

The mechanical design of a proton microscope for radiography at 800 MeV

A proton microscope has been developed for radiography applications using the 800-MeV linear accelerator at the Los Alamos Neutron Science Center (LANSCE). The microscope provides a magnified image of a static device, or of a dynamic event such as a high-speed projectile impacting a target. The microscope assembly consists primarily of four Permanent Magnet Quadrupoles (PMQs) that are supported on movable platforms. The platform supports, along with the rest of the support structure, are designed to withstand the residual dynamic loads that are expected from the dynamic tests. This paper covers the mechanical design of the microscope assembly, including the remote positioning system that allows for fine-tuning the focus of an object being imaged.

Variable-field permanent-magnet quadrupole for the SSC

A set of compact variable-field permanent-magnet quadrupoles have been designed, fabricated, and tested for use in the SSC linac matching section. The quadrupoles have 24 mm-diameter apertures and 40 mm-long poles. The hybrid (permanent-magnet and iron) design, uses a fixed core of magnet material (NdFeB) and iron (C-1006) surrounded by a rotating ring of the same magnet material and iron. The quadrupole gradient-length product can be smoothly varied from a minimum of 0.7 T up to a maximum, of 4.3 T by a 90/spl deg/ rotation of the outer ring of iron and magnet material. >

Pion production at small angles

Abstract π + and π − production cross sections for 800-MeV protons on C and Cu have been measured at laboratory angles of 0°, 3°, 5°, 7°, 10°, 15°, and 20°. Pions were analyzed using the High Resolution Proton Spectrometer (HRS) facility for momenta from 364 to 675 MeV/ c . Particle identification was made utilizing a time-of-flight method. We estimate the total systematic and statistical error to be ±15% for measurements at 0° and 3° and ±10% at other angles. These data have been used to determine the optimum energy and pion production angle for injection into a proposed superconducting accelerator for pions. Protons are the main source of contamination for a π + beam. Proton-to-pion ratios are given for laboratory angles of 5° and larger.

Ray Tracing through the Edge Focusing of Rectangular Benders and an Improved Model for the Los Alamos Proton Storage Ring

Particle ray tracing through simulated 3D magnetic fields was executed to investigate the effective quadrupole strength of the edge focusing of the rectangular bending magnets in the Los Alamos Proton Storage Ring (PSR). The particle rays receive a kick in the edge field of the rectangular dipole. A focal length may be calculated from the particle tracking and related to the fringe field integral (FINT) model parameter. This tech note introduces the baseline lattice model of the PSR and motivates the need for an improvement in the baseline models vertical tune prediction, which differs from measurement by .05. An improved model of the PSR is created by modifying the fringe field integral parameter to those suggested by the ray tracing investigation. This improved model is then verified against measurement at the nominal PSR operating set point and at set points far away from the nominal operating conditions. Lastly, Linear Optics from Closed Orbits (LOCO) is employed in an orbit response matrix method for model improvement to verify the quadrupole strengths of the improved model.