Proton Radiography Facility Research Articles

Comparison of profile measurements and TRANSPORT beam envelope predictions along the 80-m LANSCE pRad beamline

Here we report a comparison between the simulation of beam phase-space and profile distributions with diagnostic measurements. TRANSPORT, a particle transport code, was used for the prediction of a 800 MeV proton beam envelope from the end of the linac to the proton radiography (pRad) facility (a total length of 80 meters). The beam profile was measured at key positions along the beamline using wire scanners and gated CCD camera systems. These measurements were compared to their respective points along the simulated beamline. The predicted beam envelope and measured data correspond within expected errors.

Peculiarities of proton microscope development for the aims of proton radiography

Proton radiography facility based on a GeV-energy beam is expected to be useful to study the dynamic processes in matter under extreme conditions. The main factors affecting pRad facility spatial and temporal resolutions and general peculiarities of proton microscopy are described. The results of the microscope simulation for GeV-energy facility are presented.

Proton microscope design for 9 GeV pRad facility

The proton microscope design for 9 GeV proton radiography facility is described. Basic principles of proton microscope development are discussed. Two variants of microscope optical scheme are proposed. Simulation of the proton beam dynamics is carried out, the results showing the possibility to obtain the microscope spatial resolution not worse than 10 μ m.

Nonuniform radiation damage in permanent magnet quadrupoles.

We present data that indicate nonuniform magnetization loss due to radiation damage in neodymium-iron-boron Halbach-style permanent magnet quadrupoles. The proton radiography (pRad) facility at Los Alamos uses permanent-magnet quadrupoles for magnifying lenses, and a system recently commissioned at GSI-Darmsdadt uses permanent magnets for its primary lenses. Large fluences of spallation neutrons can be produced in close proximity to these magnets when the proton beam is, intentionally or unintentionally, directed into the tungsten beam collimators; imaging experiments at LANL's pRad have shown image degradation with these magnetic lenses at proton beam doses lower than those expected to cause damage through radiation-induced reduction of the quadrupole strength alone. We have observed preferential degradation in portions of the permanent magnet quadrupole where the field intensity is highest, resulting in increased high-order multipole components.

Modeling and analysis of high-explosive driven perturbed plate experiments at Los Alamos

We have carried out several experiments on the Los Alamos proton radiography (pRad) facility to explore the growth of perturbations subjected to shockless acceleration. These experiments have involved both Tantalum and depleted Uranium plates with various initial amplitudes. The experimental platform is based on the one first developed by Barnes et al. [1] and further advanced by Raevsky [2]. This paper presents both the data for these experiments and an initial attempt to model the experiments using the simulation code FLAG [3].

The effect of microstructure on Rayleigh-Taylor instability growth in solids

The effect that grain size and material processing have on high-strain rate deformation of copper has been assessed through measurements of unstable Rayleigh-Taylor (RT) perturbation growth. The dynamic loading conditions and initial sinusoidal perturbations imposed on the samples are kept constant while the microstructure of the sample material is varied. Different polycrystalline grain-sizes, single-crystal orientations, and strain-hardened samples have all been dynamically tested. The RT perturbation growth is measured by acquiring a time-sequence of radiographs using the Los Alamos National Laboratory Proton Radiography (pRad) Facility. Single-crystal orientation and stain hardening due to material processing are both observed to affect the perturbation growth. However, polycrystalline grain size variations in copper samples do not influence the growth rate under the loading conditions investigated.

Explosively driven two-shockwave tools with applications

We present the development of an explosively driven physics tool to generate two mostly uniaxial shockwaves. The tool is being used to extend single shockwave ejecta models to account for a second shockwave a few microseconds later. We explore techniques to vary the amplitude of both the first and second shockwaves, and we apply the tool experimentally at the Los Alamos National Laboratory Proton Radiography (pRad)facility. The tools have been applied to Sn with perturbations of wavelength λ = 550 μm, and various amplitudes that give wavenumber amplitude products of kh ∊ {3/4,1/2,1/4,1/8}, where h is the perturbation amplitude, and k = 2π/λ is the wavenumber. The pRad data suggest the development of a second shock ejecta model based on unstable Richtmyer-Meshkov physics.

TWAC-ITEP proton microscopy facility

A proton radiography facility with the use of magnetic optics (PUMA proton microscope) has been developed at the TWAC-ITEP accelerator-accumulator facility (the ITEP terawatt accumulator) for measuring the substance density distribution inside static and dynamic objects using the proton beam with an energy of 800 MeV. The proton radiographic image of an object of investigation placed in the object plane of the setup is formed in the plane of the detector with magnification K = 4 with the aid of the magneto-optical system consisting of four quadrupole lenses on permanent magnets. The PUMA facility is intended for measuring objects with an areal density of up to 20 g/cm2 with a field of vision as large as 20 mm in diameter. The spatial resolution of radiographic images depends strongly on the areal density of the object of investigation. For the PUMA facility, the spatial resolution varies from 60 to 115 μm at an areal density of 0.46–17 g/cm2, respectively. The dynamical state of substance can be investigated in four consecutive radiographic images, since the time structure of the proton beam consists of four pulses, each with a duration of 47 ns (full width at half maximum (FWHM)) and an interval of 250 ns between them. This article is devoted to the description of the proton microscope construction. The main metrological characteristics of the facility are described using experiments with static and dynamic objects as an example.

Qualitative comparison of bremsstrahlung X-rays and 800 MeV protons for tomography of urania fuel pellets

We present an assessment of x-rays and proton tomography as tools for studying the time dependence of the development of damage in fuel rods. We also show data taken with existing facilities at Los Alamos National Laboratory that support this assessment. Data on surrogate fuel rods have been taken using the 800 MeV proton radiography (pRad) facility at the Los Alamos Neutron Science Center (LANSCE), and with a 450 keV bremsstrahlung X-ray tomography facility. The proton radiography pRad facility at LANSCE can provide good position resolution (<70 μm has been demonstrate, 20 μm seems feasible with minor changes) for tomography on activated fuel rods. Bremsstrahlung x-rays may be able to provide better than 100 μm resolution but further development of sources, collimation, and detectors is necessary for x-rays to deal with the background radiation for tomography of activated fuel rods.

Ultra-high speed burst-mode imager for multi-frame radiography

A 720×720 pixel hybrid-CMOS imager was fabricated by Rockwell Scientific (now Teledyne Imaging Sensors). Several cameras have been in operation for 5 years, in a variety of static and dynamic experiments, at the 800 MeV proton radiography (pRAD) facility at the LANSCE accelerator. The cameras can operate with a per-pulse adjustable inter-frame time of 250 ns to 2 s, and with an exposure/integration-time as short as 150 ns. With 80 ms total readout time, the imager can be externally synchronized to 0.1–5 Hz, 50-ns wide proton beam pulses, and record 1000-frame radiographic movies of 5-to-30 min duration. The effectiveness and dependence of the global electronic shutter on the pixelated Si photo-sensor bias voltage is discussed. The spatial resolution dependence of the full imaging system on various monolithic and structured scintillators is presented. We also present features of a new-generation 10-frame, 1024×1024 pixel, 50-ns exposure, 12-bit dynamic range imager, which is now in the design phase.

Predicting image blur in proton radiography: Comparisons between measurements and Monte Carlo simulations

Abstract Given the cost and lead-times involved in high-energy proton radiography, it is prudent to model proposed radiographic experiments to see if the images predicted would return useful information. We recently modified our raytracing transmission radiography modeling code HADES to perform simplified Monte Carlo simulations of the transport of protons in a proton radiography beamline. Beamline objects include the initial diffuser, vacuum magnetic fields, windows, angle-selecting collimators, and objects described as distorted 2D (planar or cylindrical) meshes or as distorted 3D hexahedral meshes. We describe the algorithms used for simulations through typical 2D and 3D meshes. We calculate expected changes in image blur as scattering materials are placed upstream and downstream of a resolution test object (a 3 mm thick sheet of tantalum, into which 0.4 mm wide slits have been cut), and as the current supplied to the focusing magnets is varied. We compare and contrast the resulting simulations with the results of measurements obtained at the 800 MeV Los Alamos LANSCE Line-C proton radiography facility.

Application of charged particle beams of TWAC-ITEP accelerator for diagnostics of high dynamic pressure processes

The 800 MeV proton radiography facility for high dynamic pressure research in condensed matter has been commissioned at the Terrawatt Accelerator of Institute of Theoretical and Experimental Physics (TWAC-ITEP) in Moscow. Spatial resolution of the facility measured in static experiments with a variety of test objects was found to be 0.30±0.01 mm in current experimental arrangement. First dynamic experiments on the observation of a shock loading of steel surface and a propagation of the detonation wave in a high explosive charge were conducted. Good quantitative agreement of density profiles reconstructed from obtained radiographic images with theoretical and simulated data showed the capabilities of high energy ion beam radiography as an excellent tool for bulk density measurements in high dynamic pressure studies.

Proton radiography and accurate density measurements: A window into shock wave processes

Direct density measurements were made from shock-loaded aluminum and copper samples by combining plate-impact experiments with proton radiography at the Los Alamos Neutron Science Center. Flyer plates were accelerated using a 40 mm bore powder gun to create a shock wave in a sample. The sample material was then interrogated in real time using the proton radiography facility. The increase in density behind the shock front causes a measurable change in the transmission of protons through the sample, which can then be quantified as a density value in the material. Hugoniot values were calculated using more traditional techniques to evaluate the accuracy of the radiographically obtained density measurements.

An 800-MeV proton radiography facility for dynamic experiments

The capability has successfully been developed at the Los Alamos Nuclear Science Center (LANSCE) to utilize a spatially and temporally prepared 800 MeV proton beam to produce proton radiographs. A series of proton bursts are transmitted through a dynamic object and transported, via a unique magnetic lens system, to an image plane. The magnetic lens system permits correcting for the effects of multiple coulomb scattering which would otherwise completely blur the spatially transmitted information at the image plane. The proton radiographs are recorded either on a time integrating film plate or with a recently developed multi-frame electronic imaging camera system. The latter technique permits obtaining a time dependent series of proton radiographs with time intervals (modulo 358 ns) up to many microseconds and variable time intervals between images. One electronically shuttered, intensified, CCD camera is required per image. These cameras can detect single protons interacting with a scintillating fiber optic array in the image plane but also have a dynamic range which permits recording radiographs with better than 5% statistics for observation of detailed density variations in the object. A number of tests have been carried out to characterize the quality of the proton radiography system for absolute mass determination, resolution, and dynamic range. Initial dynamic experiments characterized the temporal and spatial behavior of shock propagation in a high explosive sample with up to six images per experiment. Based on experience with the prototype system, a number of upgrades are being implemented including the anticipated capability for enhanced mass discrimination through differential multiple coulomb scattering radiographs and more images with improved imaging techniques.

The Los Alamos Neutron Science Center (LANSCE)

In October 1995, with the closeout of the nuclear physics user program and the increased national need for neutrons, Los Alamos National Laboratory refocused the mission of its linear accelerator complex. The new mission called for the development and use of spallation neutron sources for research and applications. As a result, the accelerator complex formerly known as the Los Alamos Meson Physics Facility (LAMPF) is now called the Los Alamos Neutron Science Center (LANSCE). LANSCE, an acronym that formerly referred to the Manuel Lujan Jr. Neutron Scattering Center (now the Lujan Center), consists of a high-power 800–MeV proton linear accelerator (linac), a Proton Storage Ring (PSR), neutron production targets at the Lujan Center and the Weapons Neutron Research (WNR) facility, a Proton Radiography (PRad) Facility, a highpower materials irradiation area (LASREF), and an isotope production facility (IPF). With the ability to produce protons and neutrons, LANSCE is ideal for research in condensed matter science and engineering, accelerator science, nuclear science, and radiography. LANSCE uses these research capabilities to contribute to the Department of Energy Stockpile Stewardship Program and to support a national user program open to scientists from universities, industry, and federal laboratories. The layout of LANSCE can be seen at right.