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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

The multiple applications of electrons in space

An electron source such as a simple cathode is a cheap and light device which can serve several technological and scientific purposes in space: (1) electrostatic charging of a spacecraft can be limited by releasing electrons accumulated on the conductive elements of their surface; (2) the erosion of conductive coatings and the ability of conductive paints to withstand the space environment can be evaluated by monitoring the flow of charged particles impinging on their surface; (3) measuring the current collected by the spacecraft surface as a function of its potential with respect to an emitter is a very sensitive diagnostic technique which can yield a number of plasma parameters, such as density and temperature; (4) it is possible to convert the thermal motion of space plasmas into electrical energy by collecting energetic electrons and returning them to the medium as cold particles; (5) a wave in a plasma is characterized by a conduction current density which gives rise to fluctuations of the current flowing to the surface.

Grard, R. J. L.↗
NASA NTRS1981

Effects of secondary electron emission on charging

Laboratory charging studies using two electron sources with different energies show that the charging behaviors of typical spacecraft thermal control dielectric surface are extremely sensitive to the shape of their secondary emission curves. The results also suggest that the electron spectrum in a natural charging environment can be separated into three distinct regions (noninteracting, discharging, and charging) depending on the kinetic energy of the incident electron relative to the charged surface, and on the secondary emission characteristics of the material. To a first order approximation, the relative number of electrons in these different regions determines the potential of the charged surface. Detailed measurements of the secondary electron emission characteristics of Kapton, the effects of bulk conductivity and secondary emission on surface charging of these materials is reported.

Leung, M. S.↗
DOE OSTI2023

Quantum efficiency enhancement in simulated nanostructured negative electron affinity GaAs photocathodes

We report nanostructured negative electron affinity GaAs photocathodes for a polarized electron source are studied using finite difference time domain optical simulation. The structures studied are nanosquare columns, truncated nanocones, and truncated nanopyramids. Mie-type resonances in the 700–800 nm waveband, suitable for generation of polarized electrons, are identified. At resonance wavelengths, the nanostructures can absorb up to 99% of the incident light. For nanosquare columns and truncated nanocones, the maximum quantum efficiency (QE) at 780 nm obtained from simulation is 27%, whereas for simulated nanopyramids, the QE is ~21%. The high photocathode quantum efficiency is due to the shift of Mie resonance toward the longer wavelength, leading to increased light absorption. The field profile distribution shows the excitation of dipole and quadrupole modes within the nanostructures at resonant frequencies. This leads to enhanced photoabsorption and photoelectron generation closer to emission surfaces than for a flat photocathode. The enhanced photoabsorption and reduced electron transport distance for the nanostructured photocathode enhance its QE compared to that for the flat surface wafer.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2026

‘Universal Injector’ at LERF - Layout and Optics Architecture

Here, we present a next level design of a compact injector within the LERF vault, which would serve both the 22 GeV CEBAF and the positron program, while being compatible with the electron source required to produce positrons for Ce+BAF. The baseline design of a 3-pass recirculator features a main linac configured with three C-75 cryo-modules, five isochronous return arcs and three straight sections, facilitating electron beam acceleration up to 650 MeV. The Universal Injector offers flexibility of extraction 1-pass and 2-pass energy electrons, as needed for positron production, with a final 3-pass extraction required by the 650 MeV injector for 22 GeV CEBAF. This note provides an overview of the baseline optics design of the Universal Injector complex, including the 8 MeV injector merger and the recirculator racetrack, including individual extraction lines for all three passes. A comprehensive suite of beam dynamics studies to validate the design is under way; starting with the orbit correction scheme, followed by start-to-end tracking with lattice misalignments and magnet errors.

Bogacz, Alex [Thomas Jefferson National Accelerato↗
NASA NTRS1991

Long life electrodes for large-area x-ray generators

This invention is directed to rugged, reliable, and long-life electrodes for use in large-area, high-current-density electron gun and x-ray generators which are employed as contamination-free preionizers for high-energy pulsed gas lasers. The electron source at the cathode is a corona plasma formed at the interface between a conductor, or semiconductor, and a high-permittivity dielectric. Detailed descriptions are provided of a reliable cold plasma cathode, as well as an efficient liquid-cooled electron beam target (anode) and x-ray generator which concentrates the x-ray flux in the direction of an x-ray window.

Rothe, Dietmar E.↗
DOE OSTI2022

ION PRODUCTION AND MITIGATION IN DC HIGH-VOLTAGE PHOTO-GUNS

One of the biggest obstacles to operating a GaAs polarized electron source with a long charge lifetime is the mitigation of ion back-bombardment. Several techniques exist to either clear ions from the accelerator or to mitigate ion damage of the photocathode. Predicting the effectiveness of these techniques requires sophisticated simulation models of electron impact ionization within the photo-gun. In this work, the effectiveness of applying a positive anode bias voltage to mitigate ion damage and increase the charge lifetime of the GaAs photocath?ode was studied over three run periods at the Continuous Electron Beam Accelerator Facility (CEBAF) at Jefferson Lab (JLab). The charge lifetime with the biased anode configuration was 1.80±0.51 times longer than the lifetime of the usual grounded anode configuration. Sim?ulations of ionization within the CEBAF photo-gun and adjacent beamline were made using General Particle Tracer (GPT) and a new C++ custom element to predict and explain the substantial improvement in charge lifetime. The experimental results and the development of the ionization custom element, with its use in simulations of ion back-bombardment with the biased anode, are described in detail.

Yoskowitz, Joshua↗
NASA NTRS1972

Equatorial electron energy and number densities in the Jovian magnetosphere

A synchrotron model with a Maxwellian energy distribution of the form e to the (-E/E sub 0) power is used in a comparison with spatially resolved radio interferometric measurements of the Jovian emission. The observations of the decimeter radiation as a function of equatorial distance at 10.4 and 21 cm wavelength were reduced to source emission/cc of source electrons in each of 16 concentric rings. The peak energies for isotropically distributed electrons exceeded the maximum energy for flat orbiting electrons, and the peaks were generally located from 2.25 to 3 Jupiter radii. Beyond 3 radii, the order of magnitude on number density became a sensitive function of pitch angle distribution. The total equatorial intensities at 75 cm wavelength were computed for (E sub 0)(r) and n(r) at different values of B sub 0. The radiative half life for electrons of initial energy E sub 0 in a dipole field was calculated and found to be nearly constant at one year or less for altitudes at and below the position in peak energy.

Luthey, J. L.↗
DOE OSTI2025

Optimizing 4d Emittance Measurements Using the Pinhole Scan Technique

Accurate measurement of electron beam emittance is essential for optimizing high-brightness electron sources. The Pinhole Scan Technique measures the 4D phase space and hence the emittance by measuring the beam profile after clipping the beam using a pinhole followed by a drift section and then scanning the beam over the pinhole. This technique has been implemented in low energy (< 200 keV) beamlines at both Cornell University and Arizona State University. However, the technique poses several practical challenges. In this work, we analyze and address key issues affecting the 4D phase space and emittance measurements using this technique. We identify and investigate sources of inaccuracies like the pinhole aspect ratio, beam divergence, position-momentum correlations in the phase space, and the point-spread-function of the detector and suggest techniques to minimize them. Our findings offer a pathway to more accurate 4D phase space characterization in advanced electron beam systems.

42 ENGINEERING↗
DOE OSTI2023

Spatio-temporally shaped deep UV laser source for ultrabright photocathodes using novel upconversion techniques (Final Report)

The goal of this project was to take a VUV laser system designed by Kapteyn-Murnane Labs (KMLabs)—the Hyperion VUV, and increase its functionality, efficiency, and applicability by further probing the fundamental physics taking place in the system and optimizing the system performance. More specifically, DOE accelerator applications—particularly for XFELs that require low-emittance electron beams, require precisely controlled ultrashort pulses in the deep-UV at 250-260 nm to drive the photocathode electron source. This is conventionally done using an ultrafast infrared laser, with subsequent stages of nonlinear upconversion in solid-state nonlinear-optical crystal media (principally BBO, which is commonly used for UV upconversion). However, maintaining high spatial mode beam quality, as well as precisely controlled temporal profile, has proven a persistent challenge. As a possible alternative to this approach, KMLabs has demonstrated a system that generates vacuum ultraviolet light (VUV) by upconverting pulses from an infrared ultrafast laser in a gas-filled hollow waveguide, driving a process of highly cascaded harmonic generation (HCHG). Because HCHG upconversion is done in a gas, rather than a solid, at high intensity in a guided-wave geometry, it retains an excellent beam spatial profile as well as a large spectral bandwidth that allows for control over the temperal structure of the pulse. A challenge, however, is in energy scaling of this HCHG technique to the ~1-20 μJ pulses required for photocathode applications. To-date, the pulse energies used in published HCHG work are sub-10-nJ. This project proposed to explore ways to generate higher-energy pulses using HCHG, as well as to investigate spectral and temporal shaping of the deep UV pulses by pulse shaping the infrared laser used to seed the process. Although we showed that our approach works for generating light at 259 nm, the total pulse energy achieved seems limited to approximately the same value as past work. However, the techniques we investigated may well have benefits for extending this source to much shorter wavelength output.

43 PARTICLE ACCELERATORS↗
NASA NTRS2008

The Supercritical Pile GRB Model: The Prompt to Afterglow Evolution

The 'Supercritical Pile' is a very economical gamma ray burst (GRB) model that provides for the efficient conversion of the energy stored in the protons of a Relativistic Blast Wave (RBW) into radiation and at the same time produces - in the prompt GRB phase, even in the absence of any particle acceleration - a spectral peak at an energy sim 1 MeV. We extend this model to include also the evolution of the RBW Lorentz factor Gamma and thus follow the spectral and temporal features of this model into the early GRB afterglow stage. One of the novel features of the present treatment is the inclusion of the feedback of the GRB produced radiation on the evolution of Gamma with radius. This feedback and the presence of kinematic and dynamic thresholds in the model can be the sources of rich time evolution which we have begun to explore. In particular, one can this way obtain afterglow light curves with steep decays followed by the more conventional flatter afterglow slopes, while at the same time preserving the desirable features of the model, i.e. the well defined relativistic electron source and radiative processes that produce the proper peak in the nu F spectra. Furthermore, the existence of a kinematic threshold in this model provides for a operational distinction of the prompt and afterglow GRB stages; in fact, the afterglow stage sets in when the RBW Lorentz factor cannot anymore fulfill the kinematic condition for pair formation in the photon - proton pair production reactions that constitute the fundamental process for the dissipation of the blast wave kinetic energy. We present the results of a specific set of parameters of this model with emphasis on the multiwavelength prompt emission and transition to the early afterglow.

Kazanas, Demosthenes↗
NASA NTRS2009

The Supercritical Pile GRB Model: The Prompt to Afterglow Evolution

The "Supercritical Pile" is a very economical GRB model that provides for the efficient conversion of the energy stored in the protons of a Relativistic Blast Wave (RBW) into radiation and at the same time produces - in the prompt GRB phase, even in the absence of any particle acceleration - a spectral peak at energy approx. 1 MeV. We extend this model to include the evolution of the RBW Lorentz factor Gamma and thus follow its spectral and temporal features into the early GRB afterglow stage. One of the novel features of the present treatment is the inclusion of the feedback of the GRB produced radiation on the evolution of Gamma with radius. This feedback and the presence of kinematic and dynamic thresholds in the model can be the sources of rich time evolution which we have began to explore. In particular. one can this may obtain afterglow light curves with steep decays followed by the more conventional flatter afterglow slopes, while at the same time preserving the desirable features of the model, i.e. the well defined relativistic electron source and radiative processes that produce the proper peak in the (nu)F(sub nu), spectra. In this note we present the results of a specific set of parameters of this model with emphasis on the multiwavelength prompt emission and transition to the early afterglow.

Mastichiadis, A.↗
NASA NTRS2010

A Bulk Comptonization Model for the Prompt GRM Emission

The "Supercritical Pile" is a very economical GRB model that provides for the efficient conversion of the energy stored in the protons of a Relativistic Blast Wave (RBW) into radiation and at the same time produces - in the prompt GRB phase, even in the absence of any particle acceleration - a spectral peak at energy approximately 1 MeV. We extend this model to include the evolution of the RBW Lorentz factor F and thus follow its spectral and temporal features into the early GRB afterglow stage. One of the novel features of the present treatment is the inclusion of the feedback of the GRB produced radiation on the evolution of Gamma with radius. This feedback and the presence of kinematic and dynamic thresholds in the model are sources of potentially very rich time evolution which we have began to explore. In particular, one can this way obtain afterglow light curves with steep decays followed by the more conventional flatter afterglow slopes, while at the same time preserving the desirable features of the model, i.e. the well defined relativistic electron source and radiative processes that produce the proper peak in the nu F(sub nu) spectra. In this note we present the results of a specific set of parameters of this model with emphasis on the multiwavelength prompt emission and transition to the early afterglow.

Kazanas, Demos↗
DOE OSTI2023

Ion-beam-assisted growth of cesium-antimonide photocathodes

We report on the novel use of a Cs+ ion gun for an ion-beam-assisted molecular-beam-epitaxy (IBA-MBE) method to sequentially deposit Cs-Sb cathodes on room temperature substrates as opposed to the standard technique of thermal evaporation on elevated-temperature substrates. The details of the ultrahigh-vacuum chamber, the Cs+ ion source, and the growth technique are elaborated. The final quantum efficiency (QE) is reasonably good for Cs-Sb cathodes grown on two different substrates—Si (100) and strontium titanate—and is comparable to the QE of cathodes grown using thermal sources. This suggests that IBA-MBE could be a viable alternative to grow alkali-antimonides without substrate heating, paving the way for the growth of epitaxial alkali-antimonides in a more reproducible fashion, which may help improve the efficiency of photon detectors and accelerator applications that use alkali-antimonides as electron sources.

Engineering↗
DOE OSTI2023

A Novel Platform for Evaluating Dose Rate Effects on Oxidative Damage to Peptides: Toward a High-Throughput Method to Characterize the Mechanisms Underlying the FLASH Effect

High dose rate radiation has gained considerable interest recently as a possible avenue for increasing the therapeutic window in cancer radiation treatment. The sparing of healthy tissue at high dose rates relative to conventional dose rates, while maintaining tumor control, has been termed the FLASH effect. Although the effect has been validated in animal models using multiple radiation sources, it is not yet well understood. Here, in this work, we demonstrate a new experimental platform for quantifying oxidative damage to protein sidechains in solution as a function of radiation dose rate and oxygen availability using liquid chromatography mass spectrometry. Using this reductionist approach, we show that for both X-ray and electron sources, isolated peptides in solution are oxidatively modified to different extents as a function of both dose rate and oxygen availability. Our method provides an experimental platform for exploring the parameter space of the dose rate effect on oxidative changes to proteins in solution.

61 RADIATION PROTECTION AND DOSIMETRY↗
NASA NTRS1988

Advanced electric propulsion research

Results are presented which show that hollow cathodes can be operated on ammonia but that sustained operation in the high pressures where arcjet thrusters operate (of the order of 1000 Torr) is difficult to achieve. The concept of using contoured, fine wire meshes attached across the screen grid apertures in an ion thruster to effect control of the ion beam divergence is introduced. The concept is compared to conventional (free sheath) ion extraction and is shown to be potentially attractive. The performance related effects of changing the anode and cathode locations and of interchanging hollow cathode and refractory filament electron sources within an 8-cm diameter, argon, ring cusp ion thruster discharge chamber are examined. The effects induced in discharge chamber performance by changes in magnetic field strength and configuration and in propellant flow distribution are also measured. Results are presented in terms of changes in the parameters that describe the effectiveness of primary electron utilization and ion extraction into the beam. The apparatus and instrumentation used to study hollow cathode operation at high electron emission levels (of the order of 100 A) is described.

Wilbur, Paul J.↗
DOE OSTI2022

Demonstration of sub-GV/m accelerating field in a photoemission electron gun powered by nanosecond 𝑋-band radio-frequency pulses

Radio-frequency (rf) photoemission electron guns operating at higher accelerating gradients offer a pathway to produce brighter electron bunches. Brighter beams are expected to revolutionize many areas of science: they could form the backbone of next-generation compact x-ray free-electron lasers or provide coherent ultrafast quantum electron probes. We report on the experimental demonstration of an rf photoemission electron source supporting an accelerating field close to 400 MV/m at the photocathode surface without major rf breakdown or significant dark current over a 3-week experimental run. This unprecedented gradient was achieved by operating the gun in a new regime with short rf pulses, ~9ns X-band (11.7 GHz). The demonstrated paradigm provides a viable path to form relativistic electron beams with unprecedented brightness.

43 PARTICLE ACCELERATORS↗
NASA NTRS1981

Theoretical electronic transition moments for the Ballik-Ramsay, Fox-Herzberg, and Swan systems of C2

Electronic transition moments and their variation with internuclear separation are calculated for the Ballik-Ramsay (b 3 Sigma g - a 3 Pi u), Fox-Herzberg (e 3 Pi g-a 3 Pi u) and Swan (d 3 Pi g-a 3 Pi u) band systems of C2, which appear in a variety of terrestrial and astrophysical sources. Electronic wave functions of the a 3 Pi u, b 2 Sigma g -, d 3 Pi g and e 3 Pi g states of C2 are obtained by means of a self-consistent field plus configuration interaction calculation using an atomic basis of 46 Slater-type orbitals, and theoretical potential energy curves and spectroscopic constants for the four electronic states were computed. The results obtained for both the potential energy curves and electronic transition moments are found to be in good agreement with experimental data.

Cooper, D. M.↗
DOE OSTI2026

High-Efficiency, High-Current Laser-Driven Electron Injector

This final report describes research conducted under DOE Award DE-SC0021132, "High-Efficiency, High-Current Laser-Driven Electron Injector," during the period 09/01/2020–08/31/2023. The project investigates a largely unexplored regime of short-pulse laser–plasma interaction near the quarter-critical density in ultrathin gas targets as a novel electron injection mechanism for laser–wakefield acceleration (LWFA). The overarching goal is to develop high-efficiency, high-current electron sources driven by modest peak-intensity lasers at high repetition rate, suitable as compact injectors or front-ends for future laser-based accelerators.

43 PARTICLE ACCELERATORS↗