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All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Effects of the quadrupole wakefields in a passive streaker

A novel method based on transverse wakefields has been recently proposed to characterize the temporal profile of a relativistic electron bunch. The electron bunch is streaked by the interaction with the transverse wakefield excited when the electrons travel off-axis in a device called the passive streaker. Furthermore, for the large transverse off-axis offsets required to effectively streak the electron bunch, higher order modes can be excited. The time-dependent quadrupole wakefield of the dielectric-lined structure can cause a significant enlargement of the transverse profile at the screen. Consequently, the measurement resolution is decreased also at the bunch tail. We report on how the temporal profile can be effectively reconstructed also including the defocusing effect for a given transverse beam distribution at the passive streaker.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2014

Effect of Ga{sup +} irradiation in molecular-beam epitaxy grown Pt/Co/Pt thin films studied by magneto-optic spectroscopy

In-depth profile changes induced by Ga{sup +} ion irradiation in Pt(5 nm)/Co(3.3 nm)/Pt(20 nm)/Mo(20 nm) sandwiches MBE grown on Al{sub 2}O{sub 3} substrates are deduced from complex magneto-optic polar Kerr effect (PMOKE) measurements at photon energies between 1 and 5 eV. The Ga{sup +} irradiation stimulates a redistribution of Pt and Co and leads to broadening of alloyed regions at Pt-Co and Co-Pt interfaces, which is evaluated using PMOKE spectra. The effect of four Ga{sup +} fluences D between zero and 6 × 10{sup 15} Ga{sup +}/cm{sup 2} was studied. The observed PMOKE azimuth rotation peak centered at 4.5 eV reaches the maximum of 0.42° at D = 1 × 10{sup 15} Ga{sup +}/cm{sup 2} and becomes thus enhanced by a factor of 3.2 with respect to that in the non-irradiated sample. At D = 6 × 10{sup 15} Ga{sup +}/cm{sup 2} the peak amplitude falls to 0.05°. To find the in-depth profile of Co concentration s in the sandwiches as a function of D, the PMOKE azimuth rotation and ellipticity spectra are compared with a multilayer model, where ideal flat interfaces are replaced by sequences of Co{sub s}Pt{sub 1−s} layers. The dependence on D is compared with that evaluated by simulations of the structural effects of ion irradiation. At the highest D, the irradiation produces an almost complete erosion of the top Pt and Co accompanied by mixing at the Pt-Mo interface.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Reconstruction of tokamak plasma safety factor profile using deep learning

Abstract The motional Stark effect (MSE) diagnostic has been a standard measurement for the magnetic field line pitch angle in tokamaks that are equipped with neutral beams. However, the MSE data are not always available due to experimental constraints, especially in future devices without neutral beams. Here we develop a deep-learning based model (SGTC-QR) that can reconstruct the safety factor profile without the MSE diagnostic to mimic the traditional equilibrium reconstruction with the MSE constraint. The model demonstrates promising performance, and the sub-millisecond inference time is compatible with the real-time plasma control system.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2010

High homogeneity 25 cm low-energy rf ion source with inherent electron compensation

A 25 cm single-grid low-energy rf ion source with inherent electron compensation is described and characterized. Measurements were carried out using Ar and CF{sub 4} filling gas. The dependence of the ion beam current to the target as well as the current partition between the beam fast and slow ions on the rf discharge pressure for both filling gases is discussed. The unique ability of generation of coinciding ion and electron flows is demonstrated and the measured ion and electron energy distribution functions are presented as well. The developed broad ion beam source is able of providing 0.5-5 mA/cm{sup 2} current density in the low ion energy range of 50-250 eV, with possibility of independent current density and energy control. It is shown that complementing the rf plasma source with a profiling electrode allows for CF{sub 4} ion source operation attaining {+-}5% ion beam uniformity over 250 mm in diameter. The presented CF{sub 4} etching test results exhibit the possibility of highly directional anisotropic Si and SiO{sub 2} etching utilizing the developed single grid rf ion source.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Polar POLICRYPS diffractive structures generate cylindrical vector beams

Local shaping of the polarization state of a light beam is appealing for a number of applications. This can be achieved by employing devices containing birefringent materials. In this article, we present one such enables converting a uniformly circularly polarized beam into a cylindrical vector beam (CVB). This device has been fabricated by exploiting the POLICRYPS (POlymer-LIquid CRYstals-Polymer-Slices) photocuring technique. It is a liquid-crystal-based optical diffraction grating featuring polar symmetry of the director alignment. We have characterized the resulting CVB profile and polarization for the cases of left and right circularly polarized incoming beams.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Processing of GaN/Si(111) Epitaxial Structures for MEMS Applications

Two different approaches for the etching of the gallium nitride epitaxial layers grown on Si(111) substrates by plasma-assisted molecular beam epitaxy have been elaborated. It is demonstrated that anisotropic etch profiles can be achieved by both photoenhanced wet chemical etching and reactive plasma-chemical etching methods. Moreover, it is shown, that the photoenhanced wet chemical etching allows to remove GaN layer without damaging silicon substrate.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Interlaboratory Reproducibility of Contour Method Data in a High Strength Aluminum Alloy

The contour method for residual stress measurement has seen significant development, but an experimental reproducibility study utilizing physical samples has not been published. A double-blind reproducibly study is reported, having scope beginning with EDM cutting and ending with residual stress calculation. A reinforced I-beam sample geometry is identified for its unique residual stress profile when extracted from residual stress bearing quenched aluminum bar (7050-T74). Contour measurements are prescribed on a midplane of symmetry with dimensions 24.0 mm by 50.0 mm. Fourteen identically prepared samples are fabricated from a single long bar with well characterized and uniform residual stress. Five samples throughout the bar are identified for planning measurements to validate sample uniformity and overall suitability of the residual stress field. The planning measurements employ a range of techniques: contour method, neutron diffraction, and hole-drilling. Eight samples are distributed to an international group of participants to execute their standard measurement practice. A double-blind process is followed to provide anonymity. Results are provided by eight participants: six being self-similar and two being quite different, the latter set aside as outliers. An average residual stress field is established from non-outlying results and the spatial distribution of reproducibility standard deviation is determined. The average stress field ranges from -60 to 70 MPa and the reproducibility standard deviation averages 8.1 MPa on the measurement plane. The average reproducibility standard deviation is about 3 × larger for points within 1.0 mm of plane boundaries (17.6 MPa) than for the remaining points (6.1 MPa). Reproducibility standard deviation (among different labs) for contour method residual stress measurement is found to be very similar to repeatability standard deviation (in a single lab) reported in prior work. The reproducibility observed here, for the entire measurement process, is also similar to that found in a prior reproducibility study limited to contour method data analysis.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Measurement of axial neutral density profiles in a microwave discharge ion thruster by laser absorption spectroscopy with optical fiber probes

In order to reveal the physical processes taking place within the ''{mu}10'' microwave discharge ion thruster, internal plasma diagnosis is indispensable. However, the ability of metallic probes to access microwave plasmas biased at a high voltage is limited from the standpoints of the disturbance created in the electric field and electrical isolation. In this study, the axial density profiles of excited neutral xenon were successfully measured under ion beam acceleration by using a novel laser absorption spectroscopy system. The target of the measurement was metastable Xe I 5p{sup 5}({sup 2}P{sup 0}{sub 3/2})6s[{sup 3}/{sub 2}]{sup 0}{sub 2} which absorbed a wavelength of 823.16 nm. Signals from laser absorption spectroscopy that swept a single-mode optical fiber probe along the line of sight were differentiated and converted into axial number densities of the metastable neutral particles in the plasma source. These measurements revealed a 10{sup 18} m{sup -3} order of metastable neutral particles situated in the waveguide, which caused two different modes during the operation of the {mu}10 thruster. This paper reports a novel spectroscopic measurement system with axial resolution for microwave plasma sources utilizing optical fiber probes.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2014

Optical layout and mechanical structure of polarimeter-interferometer system for Experimental Advanced Superconducting Tokamak

A Far-InfaRed (FIR) three-wave POlarimeter-INTerferometer (POINT) system for measurement current density profile and electron density profile is under development for the EAST tokamak. The FIR beams are transmitted from the laser room to the optical tower adjacent to EAST via ∼20 m overmoded dielectric waveguide and then divided into 5 horizontal chords. The optical arrangement was designed using ZEMAX, which provides information on the beam spot size and energy distribution throughout the optical system. ZEMAX calculations used to optimize the optical layout design are combined with the mechanical design from CATIA, providing a 3D visualization of the entire POINT system.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2014

Propulsive performance of a finite-temperature plasma flow in a magnetic nozzle with applied azimuthal current

The plasma flow in a finite-electron-temperature magnetic nozzle, under the influence of an applied azimuthal current at the throat, is modeled analytically to assess its propulsive performance. A correction to the nozzle throat boundary conditions is derived by modifying the radial equilibrium of a magnetized infinite two-population cylindrical plasma column with the insertion of an external azimuthal body force for the electrons. Inclusion of finite-temperature effects, which leads to a modification of the radial density profile, is necessary for calculating the propulsive performance, which is represented by nozzle divergence efficiency and thrust coefficient. The solutions show that the application of the azimuthal current enhances all the calculated performance parameters through the narrowing of the radial density profile at the throat, and that investing power in this beam focusing effect is more effective than using the same power to pre-heat the electrons. The results open the possibility for the design of a focusing stage between the plasma source and the nozzle that can significantly enhance the propulsive performance of electron-driven magnetic nozzles.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Manufacturing techniques studies of ceramics by neutron and γ-ray radiography

In this study, the aim was to evaluate capabilities and constraints of radiographic imagery using thermal neutrons and gamma-rays as tools to identify the type of technique employed in ceramics manufacturing especially that used in prehistoric Brazilian pottery from Acre state. For this purpose, radiographic images of test objects made with clay of this region using both techniques - palette and rollers - have been acquired with a system comprised of a source of gamma-rays or thermal neutrons and a corresponding X-ray or neutron-sensitive Imaging Plate as detector. For the neutrongraphy samples were exposed to a thermal neutron flux of order of 10{sup 5}n.cm{sup −2}.s{sup −1} for 3 minutes at main port of Argonauta research reactor of the Instituto de Engenharia Nuclear - IEN/CNEN. The radiographic images using γ-rays from {sup 165}Dy (95 keV) and {sup 198}Au (412 keV) both produced at this reactor, have been acquired under an exposure time of a couple of hours. After acquisition, images have undergone a treatment to improve their quality through enhancement of their contrast, a procedure involving corrections of the beam divergence, sample shape and averaging of the attenuation map profile. Preliminary results show that difference between manufacturing techniques is better identified by radiography using low energy γ-rays from {sup 165}Dy rather than neutrongraphy or γ-rays from {sup 198}Au. Nevertheless, disregarding the kind of employed radiation, it should be stressed that feasibility to apply the technique is tightly tied to homogeneity of the clay itself and tempers due to their different attenuation.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

A new compact solid-state neutral particle analyser at ASDEX Upgrade: Setup and physics modeling

At ASDEX Upgrade (AUG), a new compact solid-state detector has been installed to measure the energy spectrum of fast neutrals based on the principle described by Shinohara et al. [Rev. Sci. Instrum. 75, 3640 (2004)]. The diagnostic relies on the usual charge exchange of supra-thermal fast-ions with neutrals in the plasma. Therefore, the measured energy spectra directly correspond to those of confined fast-ions with a pitch angle defined by the line of sight of the detector. Experiments in AUG showed the good signal to noise characteristics of the detector. It is energy calibrated and can measure energies of 40-200 keV with count rates of up to 140 kcps. The detector has an active view on one of the heating beams. The heating beam increases the neutral density locally; thereby, information about the central fast-ion velocity distribution is obtained. The measured fluxes are modeled with a newly developed module for the 3D Monte Carlo code F90FIDASIM [Geiger et al., Plasma Phys. Controlled Fusion 53, 65010 (2011)]. The modeling allows to distinguish between the active (beam) and passive contributions to the signal. Thereby, the birth profile of the measured fast neutrals can be reconstructed. This model reproduces the measured energy spectra with good accuracy when the passive contribution is taken into account.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Overview of results from the MST reversed field pinch experiment

An overview of recent results from the MST reversed field pinch programme is presented here. With neutral beam injection, bursty energetic particle (EP) modes are observed. The profiles of the magnetic and density fluctuations associated with these EP modes are measured using a far infrared interferometer–polarimeter. Equilibrium reconstructions of the quasi-single-helicity 3D helical state are provided by the V3FIT code that now incorporates several of MST's advanced diagnostics. The orientation of the helical structure is controlled using a new resonant magnetic perturbation technique. Gyrokinetic simulations based on experimental equilibria predict unstable trapped-electron modes (TEMs), and small-scale density fluctuations are detected in improved-confinement plasmas with TEM-like features. Upgraded pellet injection permits study of density and beta limits over MST's full range of operation, and an MST-record line-average density of 0.9 × 1020 m3 (n/nG = 1.4) has been obtained. Impurity ion temperature measurements reveal a charge-to-mass-ratio dependence in the rapid heating that occurs during a sawtooth crash. Runaway of NBI-born fast ions during the impulsive sawtooth event agrees with test-particle theory. Magnetic self-organization studies include measurements of the dynamo emf with an applied ac inductive electric field using oscillating field current drive.

beta limit↗
DOE OSTI2013

Direct Measurement of Room-Temperature Nondiffusive Thermal Transport Over Micron Distances in a Silicon Membrane

The “textbook” phonon mean free path of heat carrying phonons in silicon at room temperature is ${\sim}40\text{ }\text{ }\mathrm{nm}$. However, a large contribution to the thermal conductivity comes from low-frequency phonons with much longer mean free paths. We present here a simple experiment demonstrating that room-temperature thermal transport in Si significantly deviates from the diffusion model already at micron distances. Absorption of crossed laser pulses in a freestanding silicon membrane sets up a sinusoidal temperature profile that is monitored via diffraction of a probe laser beam. By changing the period of the thermal grating we vary the heat transport distance within the range ${\sim}1-10\text{ }\text{ }{\mu}\mathrm{m}$. At small distances, we observe a reduction in the effective thermal conductivity indicating a transition from the diffusive to the ballistic transport regime for the low-frequency part of the phonon spectrum.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2013

The effects of Doppler broadening and detector resolution on the performance of three-stage Compton cameras

Purpose: The authors investigated how the characteristics of the detectors used in a three-stage Compton camera (CC) affect the CC's ability to accurately measure the emission distribution and energy spectrum of prompt gammas (PG) emitted by nuclear de-excitations during proton therapy. The detector characteristics they studied included the material (high-purity germanium [HPGe] and cadmium zinc telluride [CZT]), Doppler broadening (DB), and resolution (lateral, depth, and energy). Methods: The authors simulated three-stage HPGe and CZT CCs of various configurations, detecting gammas from point sources with energies ranging from 0.511 to 7.12 MeV. They also simulated a proton pencil beam irradiating a tissue target to study how the detector characteristics affect the PG data measured by CCs in a clinical proton therapy setting. They used three figures of merit: the distance of closest approach (DCA) and the point of closest approach (PCA) between the measured and actual position of the PG emission origin, and the calculated energy resolution. Results: For CCs with HPGe detectors, DB caused the DCA to be greater than 3 mm for 14% of the 6.13 MeV gammas and 20% of the 0.511 MeV gammas. For CCs with CZT detectors, DB caused the DCA to be greater than 3 mm for 18% of the 6.13 MeV gammas and 25% of the 0.511 MeV gammas. The full width at half maximum (FWHM) of the PCA in the z-caret direction for HPGe and CZT detectors ranged from 1.3 to 0.4 mm for gammas with incident energy ranging from 0.511 to 7.12 MeV. For CCs composed of HPGe detectors, the resolution of incident gamma energy calculated by the CC ranged from 6% to 1% for gammas with true incident energies from 0.511 to 7.12 MeV. For CCs composed of CZT detectors, the resolution of gamma energy calculated by the CC ranged from 10% to 1% for gammas with true incident energies from 0.511 to 7.12 MeV. For HPGe and CZT CCs in which all detector effect were included, the DCA was less than 3 mm for 75% and 68% of the detected gammas, respectively, and restricting gammas to those having energy greater than 2.0 MeV increased these percentages to 83% and 77% for HPGe and CZT, respectively. Distributions of the true gamma origins and the PCA after detector characteristics had been included showed good agreement on beam range and some loss of resolution for the lateral profile of the PG emission. Characteristic energy lines were evident in the calculated gamma energy spectrum. Conclusions: The authors found the following: (1) DB is the dominant source of spatial and energy resolution loss in the CCs at all energy levels; (2) the largest difference in the spatial resolution of HPGe and CZT CCs is that the spatial resolution distributions of CZT have broader tails. The differences in the FWHM of these distributions are small; (3) the energy resolution of both HPGe and CZT three-stage CCs is adequate for PG spectroscopy; and (4) restricting the gammas to those having energy greater than 2.0 MeV can improve the achievable image resolution.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

SU-G-IeP2-04: Dosimetric Accuracy of a Monte Carlo-Based Tool for Cone-Beam CT Organ Dose Calculation: Validation Against OSL and XRQA2 Film Measurements

Purpose: The intensive use of Cone-Beam Computed Tomography (CBCT) during radiotherapy treatments raise some questions about the dose to healthy tissues delivered during image acquisitions. We hence developed a Monte Carlo (MC)-based tool to predict doses to organs delivered by the Elekta XVI kV-CBCT. This work aims at assessing the dosimetric accuracy of the MC tool, in all tissue types. Methods: The kV-CBCT MC model was developed using the PENELOPE code. The beam properties were validated against measured lateral and depth dose profiles in water, and energy spectra measured with a CdTe detector. The CBCT simulator accuracy then required verification in clinical conditions. For this, we compared calculated and experimental dose values obtained with OSL nanoDots and XRQA2 films inserted in CIRS anthropomorphic phantoms (male, female, and 5-year old child). Measurements were performed at different locations, including bone and lung structures, and for several acquisition protocols: lung, head-and-neck, and pelvis. OSLs and film measurements were corrected when possible for energy dependence, by taking into account for spectral variations between calibration and measurement conditions. Results: Comparisons between measured and MC dose values are summarized in table 1. A mean difference of 8.6% was achieved for OSLs when the energy correction was applied, and 89.3% of the 84 dose points were within uncertainty intervals, including those in bones and lungs. Results with XRQA2 are not as good, because incomplete information about electronic equilibrium in film layers hampered the application of a simple energy correction procedure. Furthermore, measured and calculated doses (Fig.1) are in agreement with the literature. Conclusion: The MC-based tool developed was validated with an extensive set of measurements, and enables the organ dose calculation with accuracy. It can now be used to compute and report doses to organs for clinical cases, and also to drive strategies to optimize imaging protocols.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

SU-G-IeP4-08: Initial Investigations of Up-Converting Nanoparticles (UCNP) for 3D Tissue Imaging in Optical-ECT

Purpose: Near-IR absorptive up-converting nanoparticles (UCNPs) is a novel contrast for optical-ECT that allows auto-fluorescence-free 3D imaging of labeled cells in a matrix of large (∼1cm{sup 3}) unsectioned normal tissue. This has the potential to image small metastases or dormant cells that is difficult with down-converting fluorescing dyes due to auto-fluorescence. The feasibility of imaging UCNP in agarose phantoms and a mouse lung is demonstrated, aided by a 3D-printed optical-ECT stage designed to excite UCNP in a mouse lung. Methods: The UCNP, NaYF{sub 4}:Yb/Er (20/2%), studied in this work up-converts 980nm light to visible light peaking sharply at ∼540nm. To characterize the UCNP emission as a function of UCNP concentration, cylindrical 2.5%wt agarose phantoms infused with UCNP at concentrations of 25µg/mL and 50µg/mL were exposed to 1.5W 980nm laser coupled to an optical fiber. The fiber was held stably at 1cm above the stage via a custom 3D-printed stage. An optically cleared lung harvested from a BALBc mice was then injected with 100µL of 1mg/mL UCNP solution ex vivo. Tomographic imaging of the UCNP emission in lung was performed. Results: The laser beam tract is visualized within the agarose phantom. A line profile of UCNP emission at 25µg/mL versus 50µg/mL shows that increasing the UCNP concentration increases emission count. UCNPs injected into a cleared mouse lung disperse throughout the respiratory tract, allowing for visualization and 3D reconstruction. Excitation before and after UCNP injection shows the tissue exhibits no auto-fluorescence at 980nm, allowing clear view of the UCNP without any obscuring features such as conventional down-converting fluorescent tags. Conclusion: We confirm that up-conversion in tissue circumvents completely tissue auto-fluorescence, which allowed background-free 3D reconstruction of the UCNP distribution. We also confirm that raising the UCNP concentration increases emission and that UCNPs are retained in agarose samples during the optical clearing process.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2023

Nitrogen thermometry in an inductively coupled plasma torch using broadband nanosecond coherent anti-Stokes Raman scattering

The development of atmospheric hypersonic flight and re-entry capabilities requires the characterization of the thermo-chemical state of representative test environments. This study demonstrates the usage of multiplex nanosecond N 2 coherent anti-Stokes Raman scattering (CARS) to measure temperatures in an atmospheric, high-temperature (>6000K), air plasma plume, generated by an inductively coupled plasma torch. These are some of the highest temperatures ever accessed via gas-phase CARS, to our knowledge. Temperatures of N 2 in the equilibrium plasma plume are determined via theoretical fits to measured CARS spectra. We discuss the practical implementation of CARS at very high temperatures, including the scaling of the N 2 CARS signal strength from 300 to 6700 K, where the expected peak signal from the high-temperature plasma torch gases is two orders of magnitude less than commonly encountered in combustion environments. An intensified CCD camera enables single-laser-shot detection at temperatures as high as 6200 K, by increasing sensitivity and providing a time gate against intense background luminosity. We also discuss the impacts of unwanted two-beam CARS contributions from outside the nominal three-beam measurement volume. We present mean axial and radial temperature profiles, as well as time-series data derived from both single-laser-shot and accumulated CARS spectra. The single-laser-shot precision is 1.7%–2.6% at temperatures of 3500 to 6200 K. The presented results pave the way for the use of CARS at very high temperatures and the measurement of spatially resolved interface processes in high-enthalpy flows.

Fries, Dan (ORCID:0000000229513294)↗