Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “vacuum electronics”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 991 records · Page 55
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Structure of bismuth films obtained using an array of identically oriented single-crystal bismuth islands preliminarily grown on a substrate

An array of identically oriented single-crystal bismuth islands formed on mica plates is used as a substrate to improve the structure of bismuth thin films grown by vacuum thermal evaporation. The array of islands is formed by the chemical etching of a single-crystal bismuth film 1 μm thick grown by floating-zone recrystallization under a coating. The structure of the obtained films is studied by X-ray diffraction, atomicforce microscopy, and electron backscatter diffraction scanning electron microscopy.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Development, construction and qualification tests of the mechanical structures of the electromagnetic calorimeter of the Mu2e experiment at Fermilab

The “muon-to-electron conversion” (Mu2e) experiment at Fermilab will search for the Charged Lepton Flavour Violating neutrino-less coherent conversion of a muon into an electron in the field of an aluminum nucleus. The observation of this process would be the unambiguous evidence of physics beyond the Standard Model. Mu2e detectors comprise a straw-tracker, an electromagnetic calorimeter and an external veto for cosmic rays. The calorimeter provides excellent electron identification, complementary information to aid pattern recognition and track reconstruction, and a fast calorimetric online trigger. The detector has been designed as a state-of-the-art crystal calorimeter and employs 1340 pure Cesium Iodide (CsI) crystals readout by UV-extended silicon photosensors and fast front-end and digitization electronics. A design consisting of two identical annular matrices (named “disks”) positioned at the relative distance of 70 cm downstream the aluminum target along the muon beamline satisfies the Mu2e physics requirements.The hostile Mu2e operational conditions, in terms of radiation levels (total ionizing dose of 12 krad and a neutron fluence of 5x1010 n/cm2 @ 1 MeVeq (Si)/y), magnetic field intensity (1 T) and vacuum level (10$^{-4}$ Torr) have posed tight constraints on the design of the detector mechanical structures and materials choice. The support structure of the two 670 crystal matrices employs two aluminum hollow rings and parts made of open-cell vacuum-compatible carbon fiber. The photosensors and service front-end electronics for each crystal are assembled in a unique mechanical unit inserted in a machined copper holder. The 670 units are supported by a machined plate made of vacuum-compatible plastic material. The plate also integrates the cooling system made of a network of copper lines flowing a low temperature radiation-hard fluid and placed in thermal contact with the copper holders to constitute a low resistance thermal bridge. The data acquisition electronics is hosted in aluminum custom crates positioned on the external lateral surface of the two disks. The crates also integrate the electronics cooling system as lines running in parallel to the front-end system.The constraints on the calorimeter mechanical structures design, the development from the conceptual design to the specifications of all the structural components, the status of components production and the components quality assurance tests are presented.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2014

Photoelectron spectroscopy of wet and gaseous samples through graphene membranes

Photoelectron spectroscopy (PES) and microscopy are highly important for exploring morphologically and chemically complex liquid–gas, solid–liquid and solid–gas interfaces under realistic conditions, but the very small electron mean free path inside dense media imposes serious experimental challenges. Currently, near ambient pressure PES is conducted using dexterously designed electron energy analyzers coupled with differentially pumped electron lenses which make it possible to conduct PES measurements at a few hPa. This report proposes an alternative ambient pressure approach that can be applied to a broad class of samples and be implemented in conventional PES instruments. It uses ultrathin electron transparent but molecular impermeable membranes to isolate the high pressure sample environment from the high vacuum PES detection system. We show that the separating graphene membrane windows are both mechanically robust and sufficiently transparent for electrons in a wide energy range to allow soft X-ray PES of liquid and gaseous water. The performed proof-of-principle experiments confirm the possibility to probe vacuum-incompatible toxic or reactive samples placed inside such hermetic, gas flow or fluidic environmental cells.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS2009

Measurements of Lunar Dust Charging Properties by Electron Impact

Dust grains in the lunar environment are believed to be electrostatically charged predominantly by photoelectric emissions resulting from solar UV radiation on the dayside, and on the nightside by interaction with electrons in the solar wind plasma. In the high vacuum environment on the lunar surface with virtually no atmosphere, the positive and negative charge states of micron/submicron dust grains lead to some unusual physical and dynamical dust phenomena. Knowledge of the electrostatic charging properties of dust grains in the lunar environment is required for addressing their hazardous effect on the humans and mechanical systems. It is well recognized that the charging properties of individual small micron size dust grains are substantially different from the measurements on bulk materials. In this paper we present the results of measurements on charging of individual Apollo 11 and Apollo 17 dust grains by exposing them to mono-energetic electron beams in the 10-100 eV energy range. The charging/discharging rates of positively and negatively charged particles of approx. 0.1 to 5 micron radii are discussed in terms of the sticking efficiencies and secondary electron yields. The secondary electron emission process is found to be a complex and effective charging/discharging mechanism for incident electron energies as low as 10-25 eV, with a strong dependence on particle size. Implications of the laboratory measurements on the nature of dust grain charging in the lunar environment are discussed.

Abbas, Mian M.↗
NASA NTRS1978

Annealing of GaAs solar cells damaged by electron irradiation

Measurements of thermal annealing of GaAlAs/GaAs solar cells damaged by 1 MeV electron irradiation are reported, and the magnitude of the short-circuit current recovery is discussed. The damaged cells are annealed in a vacuum at 200 C. A cell irradiated at 10 to the 13th power electrons per sq cm recovers all its lost short-circuit current after 15 hours of annealing. Possible application of the annealing process to solar cells in space is also considered.

Walker, G. H.↗
DOE OSTI2019

In-situ Electrochemical Testing of Uranium Oxide Alteration under Anoxic Conditions

Prediction of the corrosion behavior of spent uranium oxide (UO 2 ) fuel is needed for developing predictive performance assessment models for a geologic repository. Currently, the Fuel Matrix Dissolution Model (FMDM) is being used for modeling UO 2 chemistry in the Engineered Barrier System (EBS) and includes the effects of oxidants, oxygen and hydrogen peroxide generated from radiolysis of the fuel in contact with water, as well as the role of hydrogen on limiting corrosion. In this report, efforts to validate the FMDM model using in-situ liquid cells in the scanning electron microscopy (SEM) are described. The System for Analysis at the Liquid Vacuum Interface (SALVI), was invented at the Pacific Northwest National Laboratory (PNNL) and is a device that enables the investigation of solid-solution systems within the electron microscope. Initial efforts have concentrated on building the testing system for radioactive materials and exploring the use of the SALVI cell on UO 2 particles.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
NASA NTRS1988

Townsend coefficients for electron scattering over dielectric surfaces

A method for describing the probability of initiating flashover discharges across dielectric surfaces is presented in which a transport coefficient for electron multiplication similar to the Townsend coefficient used for gas discharges is defined. The coefficient is a function of the scaling parameter (charge released from the cathode)/(cathode-anode separation) and is also a measure of the growth of the sheath on the dielectric surface resulting from electron scattering. Results are discussed as to when the source of seed electrons does not necessarily depend upon field emission at the cathode-vacuum-dielectric triple point. For these conditions, there is a different functional dependence of flashover probability on voltage and geometry than when field emission provides the seed electrons. As a result, criteria previously used to predict flashover discharges may not apply.

Peck, Timothy L.↗
DOE OSTI2014

Ex situ elaborated proximity mesoscopic structures for ultrahigh vacuum scanning tunneling spectroscopy

We apply ultrahigh vacuum Scanning Tunneling Spectroscopy (STS) at ultra-low temperature to study proximity phenomena in metallic Cu in contact with superconducting Nb. In order to solve the problem of Cu-surface contamination, Cu(50 nm)/Nb(100 nm) structures are grown by respecting the inverted order of layers on SiO{sub 2}/Si substrate. Once transferred into vacuum, the samples are cleaved at the structure-substrate interface. As a result, a contamination-free Cu-surface is exposed in vacuum. It enables high-resolution STS of superconducting correlations induced by proximity from the underlying superconducting Nb layer. By applying magnetic field, we generate unusual proximity-induced superconducting vortices and map them with a high spatial and energy resolution. The suggested method opens a way to access local electronic properties of complex electronic mesoscopic devices by performing ex situ STS under ultrahigh vacuum.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2011

Testing a GaAs cathode in SRF gun

RF electron guns with a strained superlattice GaAs cathode are expected to generate polarized electron beams of higher brightness and lower emittance than do DC guns, due to their higher field gradient at the cathode's surface and lower cathode temperature. We plan to install a bulk GaAs:Cs in a SRF gun to evaluate the performance of both the gun and the cathode in this environment. The status of this project is: In our 1.3 GHz 1/2 cell SRF gun, the vacuum can be maintained at nearly 10{sup -12} Torr because of cryo-pumping at 2K. With conventional activation of bulk GaAs, we obtained a QE of 10% at 532 nm, with lifetime of more than 3 days in the preparation chamber and have shown that it can survive in transport from the preparation chamber to the gun. The beam line has been assembled and we are exploring the best conditions for baking the cathode under vacuum. We report here the progress of our test of the GaAs cathode in the SRF gun. Future particle accelerators, such as eRHIC and the ILC require high-brightness, high-current polarized electrons. Strained superlattice GaAs:Cs has been shown to be an efficient cathode for producing polarized electrons. Activation of GaAs with Cs,O(F) lowers the electron affinity and makes it energetically possible for all the electrons, excited into the conduction band that drift or diffuse to the emission surface, to escape into the vacuum. Presently, all operating polarized electron sources, such as the CEBAF, are DC guns. In these devices, the excellent ultra-high vacuum extends the lifetime of the cathode. However, the low field gradient on the photocathode's emission surface of the DC guns limits the beam quality. The higher accelerating gradients, possible in the RF guns, generate a far better beam. Until recently, most RF guns operated at room temperature, limiting the vacuum to {approx}10{sup -9} Torr. This destroys the GaAs's NEA surface. The SRF guns combine the excellent vacuum conditions of DC guns and the high accelerating gradient of the RF guns, potentially offering a long lived cathode with very low emittance. Testing this concept requires preparation of the cathode, transportation to the SRF gun and evaluation of the performance of the cathode and the gun at cryogenic temperatures. In our work at BNL, we successfully activated the bulk GaAs in the preparation chamber. The highest quantum efficient was 10% at 532 nm that fell to 0.5% after 100 hours. We explored three different ways to activate the GaAs. We verified that the GaAs photocathode remains stable for 30 hours in a 10{sup -11} Torr vacuum. Passing the photocathode through the low 10{sup -9} Torr transfer section in several seconds caused the QE to drop to 0.8%. The photocathode with 0.8% QE can be tested for the SRF gun. The gun and beam pipe were prepared and assembled. After baking at 200 C baking, the vacuum of the gun and beam pipe can sustain a low 10{sup -11} Torr at room temperature. The final test to extract electrons from the gun is ongoing. In this paper, we discuss our progress with this SRF gun and the results of the photocathode in preparation chamber and in magnet transfer line.

43 PARTICLE ACCELERATORS↗
DOE OSTI2011

Direct laser acceleration of electron by an ultra intense and short-pulsed laser in under-dense plasma

Direct laser acceleration (DLA) of electron by an ultra intense and short-pulsed laser interacting with under-dense plasma is investigated based on 2.5-dimensional particle-in-cell simulation. A high-density electron beam is generated by the laser longitudinal ponderomotive force. Although the total number of DLA electrons is significantly smaller than the number of electrons trapped in the bubble, the total charge of high-energy DLA electrons (E>800MeV) reaches 67 pC/{mu}m. It is found that the electron beam occurs in a two-stage acceleration, i.e., accelerated in vacuum by the laser directly soon after a DLA process in plasma. The beam is accelerated violently with effective acceleration gradient in 100 GeV/cm. The energy spectrum of electrons presents a Maxwellian distribution with the highest energy of about 3.1 GeV. The dependence of maximum electron energy and electric quantity with laser intensity, laser width, pulse duration, and initial plasma density are also studied.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Particle in cell simulation of a radiofrequency plasma jet expanding in vacuum

The effect of a pressure gradient (∼133 Pa–0.133 Pa) on electron and ion energy distributions in a radiofrequency (rf at 13.56 MHz) argon plasma jet is studied using a 1D-3v Particle In Cell (PIC) simulation. The PIC domain is three times that of the 0.018 m long plasma cavity and the total simulation time is 1 ms. Ion heating and acceleration up to a drift velocity about 2000 m s{sup −1} are measured along the jet's main expansion axis. Elastic and charge exchange ion-neutral collisions histograms computed at equilibrium during 0.74 ms show that charge exchange collisions act as the main neutral heating mechanism.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2019

RGA Analysis of Plasma Cleaned Vacuum Systems [Slides]

The goal of this project was to qualitatively evaluate the efficacy of using plasma cleaning to remove PDMS from vacuum systems. Silicon containing compounds are notorious for interfering with vacuum system techniques such as x-ray photoelectron spectroscopy (XPS), Auger Electron Spectroscopy (AES) and Secondary lon Mass Spectrometry (SIMS). Finding a way to remotely and rapidly remove contaminants from a system saves time and money for analysts using vacuum analytical techniques.

42 ENGINEERING↗
NASA NTRS1970

Quadrupole ionization gage measures ultrahigh vacuum

Quadrupole system, energized with a 200 MHz electric field, restrains ionizing electrons within the center of the ionization gage. Oscillatory trajectory of the electrons increases the probability of ionizing the gas molecules, lowers background X-ray level, and increases the signal-to-noise ratio.

Schwarz, H. J.↗
NASA NTRS1976

Electron-beam welder alinement

Parts are easily and quickly positioned in welding vacuum chamber with use of inexpensive thin metal-foil plate.

Whiffen, E. L.↗
NASA NTRS1997

Atomic, Molecular, and Optical Physics: Optical Excitation Function of H(1s-2p) Produced by electron Impact from Threshold to 1.8 keV

The optical excitation function of prompt Lyman-Alpha radiation, produced by electron impact on atomic hydrogen, has been measured over the extended energy range from threshold to 1.8 keV. Measurements were obtained in a crossed-beams experiment using both magnetically confined and electrostatically focused electrons in collision with atomic hydrogen produced by an intense discharge source. A vacuum-ultraviolet mono- chromator system was used to measure the emitted Lyman-Alpha radiation. The absolute H(1s-2p) electron impact excitation cross section was obtained from the experimental optical excitation function by normalizing to the accepted optical oscillator strength, with corrections for polarization and cascade. Statistical and known systematic uncertainties in our data range from +/- 4% near threshold to +/- 2% at 1.8 keV. Multistate coupling affecting the shape of the excitation function up to 1 keV impact energy is apparent in both the present experimental data and present theoretical results obtained with convergent close- coupling (CCC) theory. This shape function effect leads to an uncertainty in absolute cross sections at the 10% level in the analysis of the experimental data. The derived optimized absolute cross sections are within 7% of the CCC calculations over the 14 eV-1.8 keV range. The present CCC calculations converge on the Bethe- Fano profile for H(1s-2p) excitation at high energy. For this reason agreement with the CCC values to within 3% is achieved in a nonoptimal normalization of the experimental data to the Bethe-Fano profile. The fundamental H(1s-2p) electron impact cross section is thereby determined to an unprecedented accuracy over the 14 eV - 1.8 keV energy range.

James, G. K.↗
NASA NTRS1989

Electrostatic charging of spacecraft in response to electron beam injection

Electron beam injections from spacecraft now constitute a major activity in space research. Here, the charging level of a conducting surface when an electron beam is injected from it is investigated. Injections into both vacuum and an ambient plasma are considered. When a Maxwellian beam is injected into vacuum, the surface changes to a potential much greater than the average beam energy. The dependence of this excess is examined by considering beams with water-bag types of velocity distribution functions in which no electron has a velocity V(max) above a certain value. The electric field distribution in the electron sheath near the surface is determined by the pressure distribution. Thus, the surface potential is determined not only by V(max) but by all the beam parameters. The ambient plasma reduces the charging level and causes an oscillation in the surface potential. The oscillation frequency is the electron-plasma frequency associated with the ambient plasma.

Singh, Nagendra↗