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DOE OSTI2014

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.

36 MATERIALS SCIENCE↗

DOE OSTI2014

Control rod calibration and reactivity effects at the IPEN/MB-01 reactor

Researches that aim to improve the performance of neutron transport codes and quality of nuclear cross section databases are very important to increase the accuracy of simulations and the quality of the analysis and prediction of phenomena in the nuclear field. In this context, relevant experimental data such as reactivity worth measurements are needed. Control rods may be made of several neutron absorbing materials that are used to adjust the reactivity of the core. For the reactor operation, these experimental data are also extremely important: with them it is possible to estimate the reactivity worth by the movement of the control rod, understand the reactor response at each rod position and to operate the reactor safely. This work presents a temperature correction approach for the control rod calibration problem. It is shown the control rod calibration data of the IPEN/MB-01 reactor, the integral and differential reactivity curves and a theoretical analysis, performed by the MCNP-5 reactor physics code, developed and maintained by Los Alamos National Laboratory, using the ENDF/B-VII.0 nuclear data library.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗

DOE OSTI2015

Radial distribution of charged particles in a magnetic field

The radial spread of charged particles emitted from a point source in a magnetic field is a potential source of systematic error for any experiment where magnetic fields guide charged particles to detectors with finite size. Assuming uniform probability as a function of the phase along the particle’s helical trajectory, an analytic solution for the radial probability distribution function follows which applies to experiments in which particles are generated throughout a volume that spans a sufficient length along the axis of a homogeneous magnetic field. This approach leads to the same result as a different derivation given by Dubbers et al., Nucl. Instrum. Methods Phys. Res., Sect. A 763, 112–119 (2014). But the constant phase approximation does not strictly apply to finite source volumes or fixed positions, which lead to local maxima in the radial distribution of emitted particles at the plane of the detector. A simple method is given to calculate such distributions, then the effect is demonstrated with data from a {sup 207}Bi electron-conversion source in the superconducting solenoid magnet spectrometer of the Ultracold Neutron facility at the Los Alamos Neutron Science Center. Implications for neutron beta decay spectroscopy are discussed.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2015

Hugoniot equation of state and dynamic strength of boron carbide

Boron carbide ceramics have been particularly problematic in attempts to develop adequate constitutive model descriptions for purposes of analysis of dynamic response in the shock and impact environment. Dynamic strength properties of boron carbide ceramic differ uniquely from comparable ceramics. Furthermore, boron carbide is suspected, but not definitely shown, to undergoing polymorphic phase transformation under shock compression. In the present paper, shock-wave compression measurements conducted over the past 40 years are assessed for the purpose of achieving improved understanding of the dynamic equation of state and strength of boron carbide. In particular, attention is focused on the often ignored Los Alamos National Laboratory (LANL) Hugoniot measurements performed on porous sintered boron carbide ceramic. The LANL data are shown to exhibit two compression anomalies on the shock Hugoniot within the range of 20–60 GPa that may relate to crystallographic structure transitions. More recent molecular dynamics simulations on the compressibility of the boron carbide crystal lattice reveal compression transitions that bear similarities to the LANL Hugoniot results. The same Hugoniot data are complemented with dynamic isentropic compression data for boron carbide extracted from Hugoniot measurements on boron carbide and copper granular mixtures. Other Hugoniot measurements, however, performed on near-full-density boron carbide ceramic differ markedly from the LANL Hugoniot data. These later data exhibit markedly less compressibility and tend not to show comparable anomalies in compressibility. Alternative Hugoniot anomalies, however, are exhibited by the near-full-density data. Experimental uncertainty, Hugoniot strength, and phase transformation physics are all possible explanations for the observed discrepancies. It is reasoned that experimental uncertainty and Hugoniot strength are not likely explanations for the observed differences. The notable mechanistic difference in the processes of shock compression between the LANL data and that of the other studies is the markedly larger inelastic deformation and dissipation experienced in the shock event brought about by compaction of the substantially larger porosity LANL test ceramics. High-pressure diamond anvil cell experiments reveal extensive amorphization, reasoned to be a reversion product of a higher-pressure crystallographic phase, which is a consequence of application of both high pressure and shear deformation to the boron carbide crystal structure. A dependence of shock-induced high-pressure phase transformation in boron carbide on the extent of shear deformation experienced in the shock process offers a plausible explanation for the differences observed in the LANL Hugoniot data on porous ceramic and that of other shock data on near-full-density boron carbide.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2015

Weakly nonlinear Bell-Plesset effects for a uniformly converging cylinder

In this research, a weakly nonlinear (WN) model has been developed considering the growth of a small perturbation on a cylindrical interface between two incompressible fluids which is subject to arbitrary radial motion. We derive evolution equations for the perturbation amplitude up to third order, which can depict the linear growth of the fundamental mode, the generation of the second and third harmonics, and the third-order (second-order) feedback to the fundamental mode (zero-order). WN solutions are obtained for a special uniformly convergent case. WN analyses are performed to address the dependence of interface profiles, amplitudes of inward-going and outward-going parts, and saturation amplitudes of linear growth of the fundamental mode on the Atwood number, the mode number (m), and the initial perturbation. The difference of WN evolution in cylindrical geometry from that in planar geometry is discussed in some detail. It is shown that interface profiles are determined mainly by the inward and outward motions rather than bubbles and spikes. The amplitudes of inward-going and outward-going parts are strongly dependent on the Atwood number and the initial perturbation. For low-mode perturbations, the linear growth of fundamental mode cannot be saturated by the third-order feedback. For fixed Atwood numbers and initial perturbations, the linear growth of fundamental mode can be saturated with increasing m. The saturation amplitude of linear growth of the fundamental mode is typically 0.2λ–0.6λ for m < 100, with λ being the perturbation wavelength. Thus, it should be included in applications where Bell-Plesset [G. I. Bell, Los Alamos Scientific Laboratory Report No. LA-1321, 1951; M. S. Plesset, J. Appl. Phys. 25, 96 (1954)] converging geometry effects play a pivotal role, such as inertial confinement fusion implosions.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2016

Electron stripping processes of H{sup −} ion beam in the 80 kV high voltage extraction column and low energy beam transport line at LANSCE

Basic vacuum calculations were performed for various operating conditions of the Los Alamos National Neutron Science H{sup −} Cockcroft-Walton (CW) injector and the Ion Source Test Stand (ISTS). The vacuum pressure was estimated for both the CW and ISTS at five different points: (1) inside the H{sup −} ion source, (2) in front of the Pierce electrode, (3) at the extraction electrode, (4) at the column electrode, and (5) at the ground electrode. A static vacuum analysis of residual gases and the working hydrogen gas was completed for the normal ion source working regime. Gas density and partial pressure were estimated for the injected hydrogen gas. The attenuation of H{sup −} beam current and generation of electron current in the high voltage acceleration columns and low energy beam transport lines were calculated. The interaction of H{sup −} ions on molecular hydrogen (H{sub 2}) is discussed as a dominant collision process in describing electron stripping rates. These results are used to estimate the observed increase in the ratio of electrons to H{sup −} ion beam in the ISTS beam transport line.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2016

Different approaches to modeling the LANSCE H{sup −} ion source filament performance

An overview of different approaches to modeling of hot tungsten filament performance in the Los Alamos Neutron Science Center (LANSCE) H{sup −} surface converter ion source is presented. The most critical components in this negative ion source are two specially shaped wire filaments heated up to the working temperature range of 2600 K–2700 K during normal beam production. In order to prevent catastrophic filament failures (creation of hot spots, wire breaking, excessive filament deflection towards source body, etc.) and to improve understanding of the material erosion processes, we have simulated the filament performance using three different models: a semi-empirical model, a thermal finite-element analysis model, and an analytical model. Results of all three models were compared with data taken during LANSCE beam production. The models were used to support the recent successful transition from the beam pulse repetition rate of 60 Hz–120 Hz.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2016

Imaging the inside of thick structures using cosmic rays

The authors present here a new method to image reinforcement elements inside thick structures and the results of a demonstration measurement performed on a mock-up wall built at Los Alamos National Laboratory. The method, referred to as “multiple scattering muon radiography”, relies on the use of cosmic-ray muons as probes. The work described in this article was performed to prove the viability of the technique as a means to image the interior of the dome of Florence Cathedral Santa Maria del Fiore, one of the UNESCO World Heritage sites and among the highest profile buildings in existence. Its result shows the effectiveness of the technique as a tool to radiograph thick structures and image denser object inside them.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2016

Neutron imaging with the short-pulse laser driven neutron source at the TRIDENT Laser Facility

Emerging approaches to short-pulse laser-driven neutron production offer a possible gateway to compact, low cost, and intense broad spectrum sources for a wide variety of applications. They are based on energetic ions, driven by an intense short-pulse laser, interacting with a converter material to produce neutrons via breakup and nuclear reactions. Recent experiments performed with the high-contrast laser at the Trident laser facility of Los Alamos National Laboratory have demonstrated a laser-driven ion acceleration mechanism operating in the regime of relativistic transparency, featuring a volumetric laser-plasma interaction. This mechanism is distinct from previously studied ones that accelerate ions at the laser-target surface. The Trident experiments produced an intense beam of deuterons with an energy distribution extending above 100 MeV. This deuteron beam, when directed at a beryllium converter, produces a forward-directed neutron beam with ~5x10 9 n/sr, in a single laser shot, primarily due to deuteron breakup. The neutron beam has a pulse duration on the order of a few nanoseconds with an energy distribution extending from a few hundreds of keV to almost 80 MeV. For the experiments on neutron-source spot-size measurements, our gated neutron imager was setup to select neutrons in the energy range of 2.5 to 35 MeV. The spot size of neutron emission at the converter was measured by two different imaging techniques, using a knife-edge and a penumbral aperture, in two different experimental campaigns. The neutron-source spot size is measured ~1 mm for both experiments. The measurements and analysis reported here give a spatial characterization for this type of neutron source for the first time. In addition, the forward modeling performed provides an empirical estimate of the spatial characteristics of the deuteron ion-beam. Finally, these experimental observations, taken together, provide essential yet unique data to benchmark and verify theoretical work into the basic acceleration mechanism, which remains an ongoing challenge.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2017

Inverse-collimated proton radiography for imaging thin materials

Relativistic, magnetically-focused proton radiography was invented at Los Alamos National Laboratory using the 800 MeV LANSCE beam, and is inherently well-suited to imaging dense objects, at areal densities >20 g cm -2 . However, if the unscattered portion of the transmitted beam is removed at the Fourier plane through inverse-collimation, this system becomes highly sensitive to very thin media, of areal densities <100 mg cm -2 . Here, this inversecollimation scheme is described in detail and demonstrated by imaging Xe gas with a shockwave generated by an aluminum plate compressing the gas at Mach 8.8. With a 5-mrad inverse collimator, an areal density change of just 49 mg cm-2 across the shock front is discernible with a contrast-to-noise ratio of 3. Geant4 modeling of idealized and realistic proton transports can guide the design of inverse-collimators optimized for specific experimental conditions and show that this technique performs better for thin targets with reduced incident proton beam emittance. This work increases the range of areal densities to which the system is sensitive to span from ~25 mg cm -2 to 100 g cm -2 , exceeding three orders of magnitude. This enables the simultaneous imaging of a dense system, as well as thin jets and ejecta material that are otherwise difficult to characterize with high-energy proton radiography.

47 OTHER INSTRUMENTATION↗

DOE OSTI2017

Spatially and temporally resolved measurements of a dense copper plasma heated by intense relativistic electrons

A 100-μm-thick Cu foil is isochorically heated by a ~100-ns-long electron bunch with an energy of 19.8 MeV and current of 1.7 kA to T e > 1 eV. After 100 ns of heating and 20 ns of expansion, the plasma exhibits a stable, quiescent temperature and density distribution for >200 ns. Several intense Cu-I emission lines are observed after ~20 J of electron beam energy is deposited. These lines have well known Stark widths providing a direct measurement of n e . The Los Alamos ATOMIC code [Magee et al., AIP Conf. Proc. 2004, 168–179 and Hakel et al., J. Quant. Spectrosc. Radiat. Transfer 99, 265 (2006)] was run in local-thermodynamic-equilibrium mode to estimate T e and n e . Spatially and temporally resolved measurements are then presented in both the vertical and horizontal directions adjacent to the foil indicating temperatures >1 eV and densities ranging from 1–3 × 10 17 cm -3 after expansion and cooling.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2019

Requirements and sensitivity analysis for temporally- and spatially-resolved thermometry using neutron resonance spectroscopy

Neutron resonance spectroscopy (NRS) has been used extensively to make temperature measurements that are accurate, absolute, and nonperturbative within the interior of material samples under extreme conditions applied quasistatically. Yet NRS has seldom been used in dynamic experiments. There is a compelling incentive to do so because of the significant shortcomings of alternative techniques. An important barrier to adopting dynamic NRS thermometry is the difficulty in fielding it with conventional spallation neutron sources. To enable time-dependent and spatially resolved temperature measurements in dynamic environments, more compact neutron sources that can be used at user facilities in conjunction with other diagnostic probes (such as x-ray light sources) are required. Such sources may be available using ultrafast high-intensity optical lasers. We evaluate such possibilities by determining the sensitivities of the temperature estimate on neutron-beam and diagnostic parameters. Based on that evaluation, requirements are set on a pulsed neutron-source and diagnostics to make a meaningful dynamic temperature measurement. Dynamic thermometry measurements are examined in this context when driven by two alternative fast-neutron sources: the Los Alamos Neutron Scattering Center (LANSCE) proton accelerator driving isotropic spallation neutrons as a baseline and a laser-plasma ion accelerator driving a neutron beam from deuterium breakup. Strategies to close the gap between the required and demonstrated performance of laser-based fast-neutron sources are presented. A short-pulse high-intensity laser with state-of-the-art pulse contrast and an energy of a few hundred Joules would drive a compact neutron source suitable for NRS thermometry that could transform the dynamic study of materials.

47 OTHER INSTRUMENTATION↗

DOE OSTI2018

Full-waveform inversion and least-squares reverse-time migration imaging of collimated ultrasonic-beam data for high-resolution wellbore integrity monitoring

Los Alamos National Laboratory (LANL) has recently developed an ultrasonic side-lobe suppressed Bessel collimated beam transducer for low-frequency imaging through highly attenuating materials. In this paper, we study the effectiveness of using such a collimated ultrasonic-beam transducer for imaging concrete heterogeneities outside borehole casing for high-resolution borehole imaging and wellbore integrity monitoring. We obtain detailed concrete heterogeneities including a low-velocity zone using ultrasound data acquired with a 3D imaging prototype and our recently developed full-waveform inversion and least-squares reverse-time migration methods. Full-waveform inversion fits synthetic ultrasonic waveforms with recorded waveforms to build a high-resolution velocity model. Least-squares reverse-time migration produces a high-resolution structural image showing material discontinuities. Finally, our results demonstrate that LANL's 3D imaging system with a collimated ultrasonic-beam transducer together with full-waveform inversion and least-squares reverse-time migration imaging has great potential for high-resolution single-well borehole imaging and non-destructive evaluation.

47 OTHER INSTRUMENTATION↗

DOE OSTI2018

A liquid VI scintillator cell for fast-gated neutron imaging

Here, the design of a new fast-gated neutron imaging system for the National Ignition Facility with much stricter timing constraints than a previous system has prompted the search for a fast scintillator material that can be used in imaging. A novel imaging cell based on Liquid VI has recently been developed with Eljen Technology and characterized at the Special Technologies Laboratory and the Los Alamos Neutron Science Center. The results show superior timing characteristics and spatial resolution, and sufficient light production for the new system compared to fast plastic scintillators previously used in neutron imaging. While the primary application is in inertial confinement fusion diagnostics, the imaging cell can be used in any fast-gated imaging application where timing characteristics and spatial resolution are of concern.

47 OTHER INSTRUMENTATION↗

DOE OSTI2018

Gallium nitride (GaN) devices as a platform technology for radiation hard inertial confinement fusion diagnostics

Inertial Confinement Fusion (ICF) is undergoing more detailed research to increase neutron yield and will require high resolution imaging near the target. Neutron damage to diagnostics remains a serious issue in understanding and achieving ICF. We have demonstrated that Gallium Nitride (GaN) optoelectronic devices have exceptional neutron radiation hardness, by systematic testing of neutron radiation effects in GaN devices and materials with elevated neutron fluence levels and a broad neutron energy spectrum. During the 2013-2017 run cycles at Los Alamos Neutron Science Center (LANSCE), we irradiated various GaN materials and devices with fast and thermal plus resonance neutrons at several beamlines. This work presents a radiation hardness study for Aluminum Gallium Nitride and Gallium Nitride (AlGaN/GaN) deep UV LEDs irradiated at the LANSCE 4FP60R beamline. The fluence level was up to 2.4 × 10 13 neutrons/cm 2 for neutrons with energies greater than 0.1 MeV. The device performance was monitored in real time. After three years of irradiation studies, we found that the GaN devices maintained operation in the forward active region. The current and voltage relation (I-V curves) varied insignificantly in the linear region. Finally, our results demonstrate the radiation hardness needed for laser fusion diagnostics at least up to 10 17 neutron yield per shot, if the diagnostics is placed 1 m away from the target, where the neutron fluence per shot is approximately 8 × 10 11 n/cm 2 . The GaN devices can operate for multiple shots.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2018

One dimensional shock initiation of hot isostatically pressed composition B

Twelve one dimensional shock experiments have been carried out on the UK isostatically pressed Composition B (59.5% RDX, 39.5% TNT, 1% wax) comprising of seven sustained pulse experiments and three short shock experiments using the embedded gauge technique at the Los Alamos National Laboratory gas gun facility. The evolution of the reactive growth at and behind the shock front has been measured along with the run to detonation distance. Two low pressure experiments have also been carried out to obtain non-reactive equation of state data. These data have been used to create the Pop plot and Hugoniot states for the UK Comp B. The shock initiation behavior of the UK Comp B has been compared to that of the equivalent US composition. The reactive growth shows a feature that was observed in the US composition in which the wave profiles display a high level of pre-detonation noise. This was hypothesized to be due to a piezoelectric effect in the RDX crystals. The results of these experiments have shown that this effect may be localized in the ε phase at shock pressures in the region of 4.15 GPa and above.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2019

Modeling of direct-drive cylindrical implosion experiments with an Eulerian radiation-hydrodynamics code

Recent improvements to xRAGE, Los Alamos National Laboratory's Eulerian radiation-hydrodynamics code, have enabled the computation of laser-driven experiments relevant to inertial confinement fusion and high energy density physics. Here, previous directly driven cylindrical implosion experiments are modeled in order to benchmark xRAGE design simulations for future cylindrical implosion experiments, representing the first attempt to model such systems with an Eulerian code with adaptive mesh refinement. Simulations in 2D of transverse and axial cross-sections of the cylindrical target are performed, and the results are combined to form a 3D representation of the imploding cylinder. Synthetic radiographs are produced and analyzed from the simulation results, allowing for a direct comparison with experimentally measured quantities. The zeroth-order hydrodynamic trajectories of targets with no specified initial perturbation are well matched by the computations. Simulations of targets with a preimposed sinusoidal perturbation in the azimuthal direction show single-mode instability growth that is in agreement with the available data, but higher fidelity experimental measurements are required to enable more detailed comparisons. As a result, the mode growth observed in computations compares favorably with predictions of a linear theory for the ablative Rayleigh-Taylor instability.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2019

Resonant ultrasound spectroscopy: The essential toolbox

Resonant Ultrasound Spectroscopy (RUS) is an ultrasound-based minimal-effort high-accuracy elastic modulus measurement technique. RUS as described here uses the mechanical resonances (normal modes of vibration or just modes) of rectangular parallelepiped or cylindrical specimens with a dimension of from a fraction of a millimeter to as large as will fit into the apparatus. Provided here is all that is needed so that the reader can construct and use a state-of-the-art RUS system. Included are links to open-source circuit diagrams, links to download Los Alamos National Laboratory open-source data acquisition software, links to request free analysis software, procedures for acquiring measurements, considerations on building transducers, 3-D printed stage designs, and a full mathematical explanation of how the analysis software extracts elastic moduli from resonances.

47 OTHER INSTRUMENTATION↗