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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 649 records · Page 36
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

A new microphonics measurement method for superconducting RF cavities

Mechanical vibrations of the superconducting cavity, also known as microphonics, cause shifts in the resonant frequency of the cavity. In addition to requiring additional RF power, these frequency shifts can contribute to errors in the closed loop phase and amplitude regulation. In order to better understand these effects, a new microphonics measurement method was developed, and the method was successfully used to measure microphonics on the half-wave superconducting cavity when it was operated in a production style cryostat. The test cryostat held a single β=0.1 half-wave cavity which was operated at 162.5 MHz [1] and [2]. It's the first time that the National Instruments PXIe-5641R intermediate frequency transceiver has been used for microphonics measurements in superconducting cavities. The new microphonics measurement method and results will be shown and analyzed in this paper.

Gao, Zheng↗
DOE OSTI2025

First in operando transient grating spectroscopy measurements on tungsten during high flux plasma operation in PISCES-RF

This work details the construction and first in operando transient grating spectroscopy measurements conducted on PISCES-RF during plasma operation. A preliminary study on a tungsten sample with varied plasma species (Ar and D 2 ), ion flux (4 × 10 21 to 6 × 10 22 ion/m 2 /s), ion energy (5 to 80 eV), and surface temperature (20 to 200 °C) is presented. Prior to plasma exposure, the thermal diffusivity and surface acoustic wave (SAW) speed, (6.9 ± 0.2) × 10 −5 m 2 /s and (2.66 ± 0.02) km/s, were measured in situ with a thermal grating period of 12.5 μm. During Ar plasma exposure, these two quantities vary according to the sample surface temperature. At low flux and varied ion energy, D 2 plasma exposure also results in thermal diffusivity and SAW speed varying with surface temperature alone. At high flux, D 2 plasma exposure results in no convincing change to the thermal diffusivity, but the SAW speed is reduced. After returning to 20 °C, post plasma exposures, the thermal diffusivity and SAW speed almost recover to the initial value prior to exposure.

Surface acoustic wave SAW↗
DOE OSTI2015

Intense combined source of neutrons and photons for interrogation based on compact deuteron RF accelerator

Interrogation of special nuclear materials can benefit from mobile sources providing significant fluxes of neutrons (10 8 /s at 2.5 MeV, 10 10 /s at 14.1 MeV) and of photons (>10 12 /s at 1-3 MeV). We propose a source that satisfies these requirements simultaneously plus also provides, via the reaction 11 B(d,n) 12 C(γ 15.1 ), a significant flux of 15-MeV photons, which are highly penetrating and optimal for inducing photo-fission in actinides. The source is based on a compact (< 5 m) deuteron RF accelerator that delivers an average current of a few mA of deuterons at 3-4 MeV to a boron target. The accelerator consists of a short RFQ followed by efficient inter-digital H-mode structures with permanent-magnet-quadrupole beam focusing [Kurennoy et al. (2012)], which suit perfectly for deuteron acceleration at low energies. Our estimates, based on recent measurements, indicate that the required fluxes of both neutrons and photons can be achieved at ~1 mA of 4-MeV deuterons. The goal of the proposed study is to confirm feasibility of the approach and develop requirements for future full system implementation.

43 PARTICLE ACCELERATORS↗
DOE OSTI2017

Synthesis and characterization of dense Gd 2 Ti 2 O 7 pyrochlore thin films deposited using RF magnetron sputtering

Thin films of phase-pure pyrochlore Gd 2 Ti 2 O 7 have been synthesized by RF magnetron sputtering. The films were prepared from oxide targets in 50% O 2 /Ar atmosphere and deposited on 111 yttria-stabilized zirconia (YSZ) substrates at a temperature of 800 °C. The pyrochlore structure was confirmed via grazing angle X-ray diffraction and selected area electron diffraction (SAED). Transmission electron microscopy (TEM) analysis also showed that the films were dense and of uniform thickness with surface roughness of approximately 8 nm. The total conductivity measured with AC impedance spectroscopy was found to be independent of thickness and comparable in magnitude to that of bulk Gd 2 Ti 2 O 7 . Differences were observed in the Arrhenius behavior between the bulk and thin film samples and are attributed to varying states of order in the crystalline lattice compounded by different levels of background impurities.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Comparison of ANN (MLP), ANFIS, SVM, and RF models for the online classification of heating value of burning municipal solid waste in circulating fluidized bed incinerators

Highlights: • A rapid, cost-effective, and comparative methodology was proposed to evaluate the HVs of burning MSW online. • Models ranked in descending order of performance are ANFIS, RF, SVM, MLP. • A well trained model is capable of characterizing the variation trend of HVs accurately. - Abstract: The heating values, particularly lower heating values of burning municipal solid waste are critically important parameters in operating circulating fluidized bed incineration systems. However, the heating values change widely and frequently, while there is no reliable real-time instrument to measure heating values in the process of incinerating municipal solid waste. A rapid, cost-effective, and comparative methodology was proposed to evaluate the heating values of burning MSW online based on prior knowledge, expert experience, and data-mining techniques. First, selecting the input variables of the model by analyzing the operational mechanism of circulating fluidized bed incinerators, and the corresponding heating value was classified into one of nine fuzzy expressions according to expert advice. Development of prediction models by employing four different nonlinear models was undertaken, including a multilayer perceptron neural network, a support vector machine, an adaptive neuro-fuzzy inference system, and a random forest; a series of optimization schemes were implemented simultaneously in order to improve the performance of each model. Finally, a comprehensive comparison study was carried out to evaluate the performance of the models. Results indicate that the adaptive neuro-fuzzy inference system model outperforms the other three models, with the random forest model performing second-best, and the multilayer perceptron model performing at the worst level. A model with sufficient accuracy would contribute adequately to the control of circulating fluidized bed incinerator operation and provide reliable heating value signals for an automatic combustion control system.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2021

An integrated approach to understanding RF vacuum arcs

Although used in the design and costing of large projects such as linear colliders and fusion tokamaks, the theory of vacuum arcs and gradient limits is not well understood. Almost 120 years after the isolation of vacuum arcs, the exact mechanisms of the arcs and the damage they produce are still being debated. We describe our simple and general model of the vacuum arc that can incorporate all active mechanisms and aims to explain all relevant data. Our four stage model, is based on experiments done at 805 MHz with a variety of cavity geometries, magnetic fields, and experimental techniques as well as data from Atom Probe Tomography and failure analysis of microelectronics. The model considers the trigger, plasma formation, plasma evolution and surface damage phases of the RF arc. This paper also examines how known mechanisms can explain the observed sharp field dependence, fast breakdown times and observed surface damage. We update the model and discuss new features while also pointing out where new data would be useful in extending the model to a wider range of frequencies.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Antenna to Core: A New Approach to RF Modelling

A new technique for the calculation of RF waves in toroidal geometry enables the simultaneous incorporation of antenna geometry, plasma facing components (PFCs), the scrape off-layer (SOL) and core propagation [Shiraiwa et al, “HIS-TORIC: Extending core ICRF wave simulation to include realistic SOL plasmas”, Nucl. Fusion in press 10 (2017)]. The calculation of antenna coupling has been traditionally performed separately from those of core propagation whereas this method allows them to be combined permitting the modelling of such phenomena as waves reflected from plasma-vacuum boundary or cyclotron resonances back to the antenna. Calculations with this technique also naturally capture wave propagation in the SOL and its interactions with non-conforming PFCs permitting self-consistent calculation of core absorption and edge power loss.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

Time-Domain Modeling of RF Antennas and Plasma-Surface Interactions

Recent advances in finite-difference time-domain (FDTD) modeling techniques allow plasma-surface interactions such as sheath formation and sputtering to be modeled concurrently with the physics of antenna near- and far-field behavior and ICRF power flow. Although typical sheath length scales (micrometers) are much smaller than the wavelengths of fast (tens of cm) and slow (millimeter) waves excited by the antenna, sheath behavior near plasma-facing antenna components can be represented by a sub-grid kinetic sheath boundary condition, from which RF-rectified sheath potential variation over the surface is computed as a function of current flow and local plasma parameters near the wall. These local time-varying sheath potentials can then be used, in tandem with particle-in-cell (PIC) models of the edge plasma, to study sputtering effects. Particle strike energies at the wall can be computed more accurately, consistent with their passage through the known potential of the sheath, such that correspondingly increased accuracy of sputtering yields and heat/particle fluxes to antenna surfaces is obtained. The new simulation capabilities enable time-domain modeling of plasma-surface interactions and ICRF physics in realistic experimental configurations at unprecedented spatial resolution. We will present results/animations from high-performance (10k-100k core) FDTD/PIC simulations of Alcator C-Mod antenna operation.

47 OTHER INSTRUMENTATION↗
DOE OSTI2013

Crystal structure and magnetic properties of Zn{sub 0.9}Cu{sub 0.1}O{sub y} rf-sputtered thin films

Zn{sub 0.9}Cu{sub 0.01}O thin films were deposited on quartz substrates by rf-magnetron sputtering using ceramic target in pure argon gas environment. The X-ray diffraction show the polycrystalline wurtzite structure of the films. The average grain size increases from 40-100nm as thickness of the film increases. The room temperature magnetization studies show the films to be ferromagnetic. The saturation magnetization decreases with increase in film thickness.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Evolution of structural and optical properties of photocatalytic Fe doped TiO{sub 2} thin films prepared by RF magnetron sputtering

Undoped and Fe doped TiO{sub 2} thin films have been prepared by RF magnetron sputtering. Pure TiO{sub 2} thin film exhibited an amorphous-like nature. With increase in iron concentration (0–0.1 at%), the films exhibited better crystallization to anatase phase . Red shift of absorption edge was observed in the UV-vis transmittance spectra . At higher Fe concentration (0.5 at%), onset of phase transformation to rutile is noticed. Photocatalytic properties of pure and 0.1 at% Fe doped TiO{sub 2} thin films were investigated by degradation of methylene blue in UV light, visible light and light from Hg vapor lamp. 70% degradation of methylene blue was observed in the presence of Fe doped film in comparison with 3% degradation in presence of pure TiO{sub 2} film when irradiated using visible light for 2 h.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Highly oriented polycrystalline Cu{sub 2}O film formation using RF magnetron sputtering deposition for solar cells

Room temperature sputtering deposition and re-crystallization of the deposited thin films by rapid thermal annealing have been evaluating in detail as a formation method of Cu{sub 2}O active layer for solar cells, which minimize thermal budget in fabrication processes. Single phase polycrystalline Cu{sub 2}O films were obtained by a magnetron rf sputtering deposition and its crystallinity and electrical characteristics were controlled by the annealing. Hall mobility was improved up to 17 cm{sup 2}V{sup −1}s{sup −1} by the annealing at 600°C for 30s. Since this value was smaller than 47 cm{sup 2}V{sup −1}s{sup −1} of the film deposited under thermal equilibrium state using pulsed laser deposition at 600°C, some contrivances were necessary to compensate the deficiency. It was understood that the sputter-deposited Cu{sub 2}O films on (111)-oriented Pt films were strongly oriented to (111) face also by the self-assembly and the crystallinity was improved by the annealing preserving its orientation. The sputter-deposited film quality was expected to become equivalent to the pulsed laser deposition film from the results of X-ray diffractometry and photoluminescence.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Fabrication of super-hydrophobic surfaces on aluminum alloy substrates by RF-sputtered polytetrafluoroethylene coatings

In this work, we present a method of fabricating super-hydrophobic surface on aluminum alloy substrate. The etching of aluminum surfaces has been performed using Beck's dislocation etchant for different time to create micrometer-sized irregular steps. An optimised etching time of 50 s is found to be essential before polytetrafluoroethylene (PTFE) coating, to obtain a highest water contact angle of 165±2° with a lowest contact angle hysteresis as low as 5±2°. The presence of patterned microstructure as revealed by scanning electron microscopy (SEM) together with the low surface energy ultrathin RF-sputtered PTFE films renders the aluminum alloy surfaces highly super-hydrophobic.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Local elastic modulus of RF sputtered HfO{sub 2} thin film by atomic force acoustic microscopy

Atomic force acoustic microscopy (AFAM) is a useful nondestructive technique for measurement of local elastic modulus of materials at nano-scale spatial resolution by measuring the contact resonance spectra for higher order modes of the AFM cantilever. The elastic modulus of RF sputtered HfO{sub 2} thin film has been measured quantitatively, using reference approach in which measurements are performed on the test and reference samples. Using AFAM, the measured elastic modulus of the HfO{sub 2} thin film is 223±27 GPa, which is in agreement with the literature value of 220±40 GPa for atomic layer deposited HfO{sub 2} thin film using nanoindentation technique.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Cleaning of optical surfaces by capacitively coupled RF discharge plasma

In this paper, we report cleaning of carbon capped molybdenum (Mo) thin film by in-house developed radio frequency (RF) plasma reactor, at different powers and exposure time. Carbon capped Mo films were exposed to oxygen plasma for different durations at three different power settings, at a constant pressure. After each exposure, the thickness of the carbon layer and the roughness of the film were determined by hard x-ray reflectivity measurements. It was observed that most of the carbon film got removed in first 15 minutes exposure. A high density layer formed on top of the Mo film was also observed and it was noted that this layer cannot be removed by successive exposures at different powers. A significant improvement in interface roughness with a slight improvement in top film roughness was observed. The surface roughness of the exposed and unexposed samples was also confirmed by atomic force microscopy measurements.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Structure and mechanical properties of 3dTM ion doped RF sputtered ZnO thin films on Si (100)

Mn, Fe and Mn-Fe doped ZnO thin films were deposited on Si (100) substrates by rf- magnetron sputtering using ceramic target in pure oxygen gas environment. The X-ray diffraction shows the polycrystalline wurtzite structure films. The average grain size varies from 32-50 nm, with lower grain size for Fe doped ZnO films. The room temperature loading and unloading curve are continuous without any pop-in. The Young's modulus and hardness are in the range 156-178 GPa and 14-15.5 GPa respectively.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Microwave properties of RF- sputtered ZnFe{sub 2}O{sub 4} thin films

In this work, RF- magnetron sputtering technique has been employed to deposit nanocrystalline ZnFe{sub 2}O{sub 4} thin films at room temperature. The as grown films were ex-situ annealed in air for 2 h at temperatures from 150°C to 650°C. X-ray diffraction, vibrating sample magnetometer and ferromagnetic resonance were used to analyze the phase formation, magnetic properties and microwave properties respectively. From the hysteresis loops and ferromagnetic resonance spectra taken at room temperature, a systematic study on the effect of O{sub 2} plasma on microwave properties with respect to processing temperature has been carried out.

36 MATERIALS SCIENCE↗
DOE OSTI2014

High total dose proton irradiation effects on silicon NPN rf power transistors

The effects of 3 MeV proton irradiation on the I-V characteristics of NPN rf power transistors were studied in the dose range of 100 Krad to 100 Mrad. The different electrical characteristics like Gummel, current gain and output characteristics were systematically studied before and after irradiation. The recovery in the I-V characteristics of irradiated NPN BJTs were studied by isochronal and isothermal annealing methods.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Determination of the density of the defect states in Hf{sub 0.5}Zr{sub 0.5}O{sub 2} high-k film Deposited by using rf-magnetron sputtering technique

A memory structure Pt/Al{sub 2}O{sub 3}/Hf{sub 0.5}Zr{sub 0.5}O{sub 2}/Al{sub 2}O{sub 3}/p-Si was fabricated by using atomic layer deposition and rf-magnetron sputtering techniques, and its microstructure has been investigated by using the high resolution transmission electron microscopy (HRTEM). By measuring the applied gate voltage dependence of the capacitance for the memory structure, the planar density of the trapped charges in Hf{sub 0.5}Zr{sub 0.5}O{sub 2} high-k film was estimated as 6.63 × 10{sup 12} cm{sup −2}, indicating a body defect density of larger than 2.21 × 10{sup 19} cm{sup −3}. It is observed that the post-annealing in N{sub 2} can reduces the defect density in Hf{sub 0.5}Zr{sub 0.5}O{sub 2} film, which was ascribed to the occupancy of oxygen vacancies by nitrogen atoms.

36 MATERIALS SCIENCE↗