Brian J. Hollander

Magnifying lens for 800 MeV proton radiography

This article describes the design and performance of a magnifying magnetic-lens system designed, built, and commissioned at the Los Alamos National Laboratory (LANL) for 800 MeV flash proton radiography. The technique of flash proton radiography has been developed at LANL to study material properties under dynamic loading conditions through the analysis of time sequences of proton radiographs. The requirements of this growing experimental program have resulted in the need for improvements in spatial radiographic resolution. To meet these needs, a new magnetic lens system, consisting of four permanent magnet quadrupoles, has been developed. This new lens system was designed to reduce the second order chromatic aberrations, the dominant source of image blur in 800 MeV proton radiography, as well as magnifying the image to reduce the blur contribution from the detector and camera systems. The recently commissioned lens system performed as designed, providing nearly a factor of three improvement in radiographic resolution.

Proton Radiography Peers into Metal Solidification

Historically, metals are cut up and polished to see the structure and to infer how processing influences the evolution. We can now peer into a metal during processing without destroying it using proton radiography. Understanding the link between processing and structure is important because structure profoundly affects the properties of engineering materials. Synchrotron x-ray radiography has enabled real-time glimpses into metal solidification. However, x-ray energies favor the examination of small volumes and low density metals. Here we use high energy proton radiography for the first time to image a large metal volume (>10,000 mm3) during melting and solidification. We also show complementary x-ray results from a small volume (<1 mm3), bridging four orders of magnitude. Real-time imaging will enable efficient process development and the control of structure evolution to make materials with intended properties; it will also permit the development of experimentally informed, predictive structure and process models.

Proton radiography: its uses and resolution scaling

A new technique in charged particle radiography was invented in 1995 at Los Alamos National Laboratory utilizing the 800MeV proton beam at the Los Alamos Neutron Science Center (LANSCE).At present proton radiography (pRad) has proven to be useful in the study of explosives driven dynamic phenomena, and quasi-static systems such as metal eutectics. For static objects, tomographic imaging has been demonstrated with possible use to study failure mechanism in materials such as nuclear fuel pellets. The basic principles of pRad will be presented along with selected representative results.

The PHELIX pulsed power project: Bringing portable magnetic drive to proton radiography

The PHELIX pulsed power project will introduce magnetically driven hydrodynamics experiments to the Los Alamos National Laboratorys proton radiography facility (pRad). The Precision High Energy-density Liner Implosion eXperiment (PHELIX) has been commissioned at Los Alamos. A small footprint capacitor bank consisting of four parallel, air-insulated, single-stage, marx units (U ~ 300 kJ) is cable coupled to a toroidal, current step-up transformer to deliver multi-megampere current pulses (tpulse ~10 μs) to cm size cylindrical loads. In a sequence of tests the performance of each component (capacitor bank and transformer) was evaluated and compared to a computer model. The transformer coupling was observed to be k ~ 0.93. A series of liner implosion experiments has been performed in which an aluminum liner (R ~3 cm, r = 0.8 mm, L = 3 cm) was accelerated to a velocity of ~ 1 km/s. The suite of machine diagnostics included linear Rogowski coils and Faraday rotation for current measurements. The experimental diagnostics include B-dot probes, multi-channel photon Doppler velocimetry (PDV), and single-frame, flash X-radiography to evaluate the performance of the high precision liner implosion. Currently, work is focused on integrating PHELIX into normal operations with the 800 MeV proton radiography facility at the Los Alamos Neutron Science Center (LANSCE), to enable high-resolution, high-frame-rate imaging of hydrodynamic experiments.