Electron beams from a duoplasmatron using a hollow cathode arc as electron source
Electron beams from duoplasmatron using hollow cathode arc, noting current density distributions
CURRENT DENSITY↗
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Absolute efficiency measurements for channel electron multipliers utilizing a unique electron source
Electron accelerator with broad stable beam for calibration of spectrometers and channel electron multipliers
Chappell, C. R.↗
Towards advanced polarized electron sources
Polarized electrons play an important role in high-energy and nuclear physics, and their properties have also been exploited in ultrafast electron microscopy. Currently, gallium arsenide crystals illuminated by circular polarized infrared laser light are commonly used for generating polarized electrons. However, the achievable accelerating voltage and the gradient of these electrostatic sources limit the beam quality and quantity. A solution could be to combine gallium arsenide photocathodes with radio-frequency electron guns, which are capable of accelerating beams with significantly higher gradients and voltage. Here we report the successful operation of a gallium arsenide photocathode in a superconducting radio-frequency gun. Our findings are relevant for future sources of polarized electrons.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Radially uniform electron source
A thermionic electron source capable of producing uniform count rates in a number of channel electron multipliers simultaneously was required for conditioning multipliers for an extended space mission. It was found that a straight tungsten filament in the center of a cylindrically symmetric geometry surrounded by an array of multipliers emits a radially asymmetric distribution of electrons that changes with time. A source was developed which successfully produces a time-independent radially uniform distribution of electrons by moving the filament out of the direct line of sight and replacing it with a centrally located electron 'cloud.'
Mccomas, D.↗
Effect of electron–electron interactions on the emission characteristics of ultracold, nanoscale photoemission-based electron sources
For nearly 60 years, cold field emitters have been the source of choice for electron microscopy due to their high brightness and relatively low energy spread. In this paper, we have examined an alternative: nanoscale electron sources based on near-threshold photoemission. While these sources have not yet been realized, they hold the potential to produce significantly brighter beams than cold field emitters. We model electron–electron Coulomb interactions in beams emitted from such sources to calculate the impact of these interactions on the brightness and the energy spread. Our results show that these sources can theoretically deliver more than an order of magnitude brighter electron beams compared to cold field emitters along with more than an order of magnitude smaller energy spread, before being limited by the Coulomb interactions. Electron sources with such high brightness and low energy spread would be transformational for electron microscopy, enabling electron energy loss-based vibrational spectroscopy at the sub-nanometer scale.
Gevorkyan, G S↗
Impact assessment of geomagnetic induced current neutral blocking devices with power electronics sources on distance relay for 230 kV transmission lines
Electrical grids increased the integration of power electronics sources onto transmission lines. In addition, recent reports show a significant rise in geomagnetic storms occurring in 2024. These geomagnetic storms can affect transmission lines by inducing electrical currents within them, potentially causing power outages due to overloaded power transformers. Geomagnetic induced current neutral blocking devices (GIC-NBDs) are capacitors on the ground of wye power transformers, to avoid damage caused by geomagnetic storms. The integration of distance relays and transmission lines with power electronics sources and GIC-NBDs needs to be studied to observe if GIC-NBDs and power electronics sources could adversely affect operation of the electrical grid. In this analysis, the effect of 2 MW power electronics sources and GIC-NBDs on distance relays is assessed for different 230 kV transmission line lengths in radial and nonradial power systems. The simulations measured the apparent impedances, with different electrical faults. Results for a typical 2,650 μF GIC-NBD application were presented on impedance plots, and the distance relay model operations were assessed. In conclusion, the tests for radial and nonradial power systems showed the behavior of the distance elements and source impedance ratios, assessing the effect of power electronics sources and GIC-NBDs on 230 kV transmission lines.
Distance relays↗
Pulsed laser deposition assisted epitaxial growth of cesium telluride photocathodes for high brightness electron sources
The development of high-brightness electron sources is critical to state-of-the-art electron accelerator applications like X-ray free electron laser (XFEL) and ultra-fast electron microscopy. Cesium telluride is chosen as the electron source material for multiple cutting-edge XFEL facilities worldwide. This manuscript presents the first demonstration of the growth of highly crystalized and epitaxial cesium telluride thin films on 4H-SiC and graphene/4H-SiC substrates with ultrasmooth film surfaces. The ordering of the film was characterized by in situ reflection high energy electron diffraction and multiple X-ray diagnostics. The results of the quantum efficiency performance for epitaxial cesium telluride photocathodes are also reported.
43 PARTICLE ACCELERATORS↗
Cold electron sources for mass spectrometric applications.
Cold electron sources using tantalum photocathodes for ionizing gas molecules for mass spectrometer application
MASS SPECTROMETER↗
Further development of the multipactor discharge electron source
A modification to the multipactor electron source used in the study of the behavior of spacecraft insulating materials is described. The electron accelerating system was included within the source, freeing the region between the source and the target of fields produced by the source electrodes.
Nanevicz, J. E.↗
Single layer graphene protective layer on GaAs photocathodes for spin-polarized electron source
GaAs-based photocathodes are the primary choice for polarized electron sources, commonly used in polarized electron microscopes and polarized positron sources. GaAs photocathodes are typically activated with cesium and oxygen, which are highly reactive and require an ultra-high vacuum (~ 10 -11 Torr or lower) to operate reliably, resulting in substantial operational difficulties. A short exposure to a mediocre vacuum results in an instantaneous loss of cathode quantum efficiency (QE) due to the chemical reaction of the active layer with residual gas molecules or back-bombardment ions during operation. Covering the GaAs cathode with a 2D material, such as monolayer graphene, could provide protection against such damage due to the inhibition of chemical reactions with residual gas molecules. In this paper, we have incorporated a method known as intercalation to pass the active material underneath the graphene and activate the superlattice GaAs/GaAsP (SL-GaAs) photocathode. X-ray photoelectron spectroscopy, low-energy electron microscopy, and Mott scattering measurements were performed to evaluate the formation of the photocathode under graphene, as well as its spectral response and electron spin polarization. Our results demonstrate that the successful activation of the SL-GaAs photocathode with a graphene protection layer is achieved with a moderate QE. Furthermore, we found that the electron spin polarization of the cathode with a surface protection layer is higher than the conventional cathode without a protection layer.
2D materials↗
Basic experimental research leading to improved cold electron sources and new types of velocity filter mass spectrometers Final report
Long duty cycle mass spectrometer for space research and source of cold electrons for ionizing neutral gas molecules in mass spectrometer
GASEOUS IONIZATION↗
High-Performance Electron Sources: Numerical Methods and Beam Dynamics at the Precision Frontier
Electron sources have a wide range of applications and there are many stakeholders that express continuing need for improvements and performance enhancements. Whether we consider ultra-cold, high-brightness, high-charge or high-average current source needs, there are some common themes from the point of view of the beam dynamics involved. These are the following ones: ability to model accurately the emission processes, including the presence of often complicated cathode and other boundary surfaces with a wide range of spatial scales; ability to deal accurately and efficiently with a large number of particles interacting pair-wise, including the stochastic part of these interactions with a wide range of spatial scales; and ability to propagate the particle distributions in time, including collisions with a wide range of temporal scales. These tasks require high precision and accuracy since the goal is usually generation, transport and preservation of very high-quality beams. This grant addressed one of the rem
43 PARTICLE ACCELERATORS↗
Harnessing Plasmonic Interference for Nanoscale Ultrafast Electron Sources
In this Letter we demonstrate the use of plasmonic focusing in conjunction with nonlinear photoemission to develop geometrically flat nanoscale electron sources with less than 40 pm-rad root mean squared (rms) normalized transverse emittance. Circularly polarized light is incident on a gold Archimedean spiral structure to generate surface-plasmon polaritons that interfere coherently at the center resulting in a 50 nm rms emission area. Furthermore, such a nanostructured flat surface enables simultaneous spatiotemporal confinement of emitted electrons at the nanometer and femtosecond level and can be used as an advanced electron source for high-repetition-rate ultrafast electron diffraction and microscopy experiments as well as the next generation of miniaturized particle accelerators.
43 PARTICLE ACCELERATORS↗
A New Electron Source for Laboratory Simulation of the Space Environment
We have developed a new collimated electron source called the Photoelectron Beam Generator (PEBG) for laboratory and spaceflight applications. This technology is needed to replace traditional cathodes because of serious fundamental weaknesses with the present state of the art. Filament cathodes suffer from numerous practical problems, even if expertly designed, including the dependence of electron emission on filament temperature, short lifetimes (approx 100 hours), and relatively high power (approx 10s of W). Other types of cathodes have solved some of these problems, but they are plagued with other difficult problems, such as the Spindt cathode's extreme sensitivity to molecular oxygen. None to date have been able to meet the demand of long lifetime, robust packaging, and precision energy and flux control. This new cathode design avoids many common pitfalls of traditional cathodes. Specifically, there are no fragile parts, no sensitivity to oxygen, no intrinsic emission dependencies on device temperature, and no vacuum requirements for protecting the source from contamination or damage. Recent advances in high-brightness Light Emitting Diodes (LEDs) have provided the key enabling technology for this new electron source. The LEDs are used to photoeject electrons off a target material of a low work-function, and these photoelectrons are subsequently focused into a laminar beam using electrostatic lenses. The PEBG works by illuminating a target material and steering photoelectrons into a laminar beam using electrostatic lenses
Krause, Linda Habash↗
An evaluation of thin film electron sources for use in ionization gauges
Tri-layer thin metal films for electron sources in mass spectrometers and ionization gauges
MASS SPECTROMETER↗
DOE Phase II Final Technical Report Bright Electron Source for X-ray Free Electron Lasers Award Number DE-SC0020607 Prepared for U.S. Department of Energy, Office of Science, SC-1 For the Period May 3, 2021 – August 2, 2024 Report Date November 25, 2024 Submitted by Harish B. Bhandari, Ph.D., Principal Investigator Report Contributors Dr. Oleg Maksimov, RMD Inc. Dr. Bryan Rachmilowitz, RMD Inc. Dr. Jared Maxson, Cornell University Dr. Hisato Yamaguchi, LANL
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Bhandari, Harish↗
BASIC EXPERIMENTAL RESEARCH LEADING TO IMPROVED COLD ELECTRON SOURCES AND NEW TYPES OF VELOCITY FILTER MASS SPECTROMETERS.
Cold electron sources and new types of velocity filter mass spectrometers
ELECTRON↗
Modeling strain and quantum confinement in GaAs/Ga x In 1−x P superlattices for spin-polarized electron sources
In this study, we systematically design and simulate a series of GaAs-based superlattice configurations aimed at enhancing heavy-hole–light-hole band splitting while simultaneously optimizing band alignment to reduce the conduction band barrier, thereby facilitating efficient electron transport. These combined effects are crucial for achieving high electron spin polarization and high quantum efficiency, the two key performance metrics of next-generation spin-polarized electron sources. We investigated three types of superlattice architectures: (1) compressively strained GaAs wells on GaInP barriers, yielding a maximum band splitting of 140 meV, (2) lattice-matched GaAs/GaInP structures, resulting in the maximum band splitting of 75 meV, and (3) tensile strained GaAs wells on GaInP barriers, with a maximum band splitting of 40 meV. The results demonstrate the tunability of heavy-hole–light-hole band splitting and establish a design framework for high-performance spin-polarized photocathodes based on a combination of strain engineering, quantum confinement, and optimized heterostructure design.
Electron sources↗