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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 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Positron beams at Ce+BAF

Positron beams would provide a new and meaningful probe for the experimental program at the Thomas Jefferson National Accelerator Facility (JLab). The JLab Positron Working Group, formed in 2018 and now with over 250 members from 75 institutions, continues to develop an experimental program with high duty-cycle positron beams including but not limited to future hadronic physics and dark matter experiments. Critical requirements involve generating positron beams with a high degree of spin polarization, sufficient intensity and a continuous-wave (CW) bunch train compatible with acceleration to 12 GeV at the Continuous Electron Beam Accelerator Facility (CEBAF). In this presentation we describe a start-to-end layout for positron beams at 12 GeV CEBAF utilizing the Low Energy Research Facility (LERF) at Jefferson Lab to build two new injectors. A GaAs dc high voltage photo-gun first generates >1 mA of polarized electrons which are then accelerated to 80-150 MeV and directed to a high-power spinning W target for polarized bremsstrahlung and positron pair creation. A second injector then collects, bunches and accelerates the positrons to 123 MeV. The positron beams are transported by a new beam line and injected into the CEBAF acceptance for acceleration to the end stations with energies up to 12 GeV. The layout is optimized to provide Users with positron spin polarization >60% and intensity greater than >100 nA, and with higher intensities when polarization is not required.

Benesch, J.↗
DOE OSTI2021

Redesign of the Jefferson Lab -300 kV DC Photo-Gun for High Bunch Charge Operations

Production of high bunch charge beams for the Electron-Ion Collider (EIC) is a challenging task. High bunch charge (a few nC) electron beam studies at Jefferson Lab using an inverted insulator DC high voltage photo-gun showed evidence of space charge limitations starting at 0.3 nC, limiting the maximum delivered bunch charge to 0.7 nC for beam at -225 kV, 75 ps (FWHM) pulse width, and 1.64 mm (rms) laser spot size. The low extracted charge is due to the modest longitudinal electric field (Ez) at the photocathode leading to beam loss at the anode and downstream beam pipe. To reach the few nC high bunch charge goal, and to correct the beam deflection exerted by the non-symmetric nature of the inverted insulator photo-gun the existing photo-gun was modified. This contribution discusses the electrostatic design of the modified photo-gun obtained using CST Studio Suite’s electromagnetic field solver. Beam dynamics simulations performed using General Particle Tracer (GPT) with the resulting electrostatic field map obtained from the modified electrodes confirmed the validity of the new design.

Wijethunga, S.A.K.↗
DOE OSTI2023

Polarized electron injector for positron production at CEBAF

As a part of the effort to expand the capabilities of CE-BAF 12 GeV (Continuous Electron Beam Accelerator Facility) at Jefferson Lab, the addition of a polarized positron source is considered. This capability would provide acceleration of high duty-cycle polarized posi-trons, with spin >60% polarization, through the same main CEBAF accelerator machine with appropriate mag-net field reversals and linac phasing to the four CEBAF experimental halls. To produce this positron beam, a high average current (3-10 mA) highly polarized electron beam with energy of 100 ? 150 MeV is required at the positron source target. The focus of this paper is the de-sign of that polarized electron beam injector. We will describe the production and delivery of a >3 mA highly polarized electron beam. We will discuss different aspects of the design, the photocathode gun, beam dynamics simulation results, spin manipulation, bunching and accelerating process and final electron beam parameters.

Kazimi, R.↗
NASA NTRS1970

Color television system using single gun color cathode ray tube

Two-primary color and single gun system provides quality differential color and variation in brightness for specific colors by varying current and controlling duty cycle of electron beam. Number of video amplifiers, deflection circuits, and guns required to display color TV picture is reduced and less complex tube is required.

Gaiser, E. E.↗
NASA NTRS2000

Three-Dimensional Electron Optics Model Developed for Traveling-Wave Tubes

A three-dimensional traveling-wave tube (TWT) electron beam optics model including periodic permanent magnet (PPM) focusing has been developed at the NASA Glenn Research Center at Lewis Field. This accurate model allows a TWT designer to develop a focusing structure while reducing the expensive and time-consuming task of building the TWT and hot-testing it (with the electron beam). In addition, the model allows, for the first time, an investigation of the effect on TWT operation of the important azimuthally asymmetric features of the focusing stack. The TWT is a vacuum device that amplifies signals by transferring energy from an electron beam to a radiofrequency (RF) signal. A critically important component is the focusing structure, which keeps the electron beam from diverging and intercepting the RF slow wave circuit. Such an interception can result in excessive circuit heating and decreased efficiency, whereas excessive growth in the beam diameter can lead to backward wave oscillations and premature saturation, indicating a serious reduction in tube performance. The most commonly used focusing structure is the PPM stack, which consists of a sequence of cylindrical iron pole pieces and opposite-polarity magnets. Typically, two-dimensional electron optics codes are used in the design of magnetic focusing devices. In general, these codes track the beam from the gun downstream by solving equations of motion for the electron beam in static-electric and magnetic fields in an azimuthally symmetric structure. Because these two-dimensional codes cannot adequately simulate a number of important effects, the simulation code MAFIA (solution of Maxwell's equations by the Finite-Integration-Algorithm) was used at Glenn to develop a three-dimensional electron optics model. First, a PPM stack was modeled in three dimensions. Then, the fields obtained using the magnetostatic solver were loaded into a particle-in-cell solver where the fully three-dimensional behavior of the beam was simulated in the magnetic focusing field. For the first time, the effects of azimuthally asymmetric designs and critical azimuthally asymmetric characteristics of the focusing stack (such as shunts, C-magnets, or magnet misalignment) on electron beam behavior have been investigated. A cutaway portion of a simulated electron beam focused by a PPM stack is illustrated.

Kory, Carol L.↗
DOE OSTI2021

Built-in Thermionic Electron Source for an SRF Linacs

The design of a thermionic electron source connected directly to a superconducting cavity, the key part of an SRF gun, is described. The results of beam dynamics optimization are presented which allow lack of beam current intercepting in the superconducting cavity. The electron source concept is presented including the cathode-grid assembly, thermal insulation of the cathode from the cavity, and the gun resonator design. The cavity thermal load caused by the gun is analyzed including the static heat load, black body radiation, backward electron heating, etc.

43 PARTICLE ACCELERATORS↗
NASA NTRS1980

Electron energy distributions measured during electron beam/plasma interactions

In the large vacuum facility at the NASA-Johnson Space Center an electron beam was projected 20 m parallel to B from a gun with variable accelerating potential (1.0 to 2.5 kV) to an aluminum target. The ionospheric neutral pressure and field were approximated. Beam electron energy distributions were measured directly using an electrostatic deflection analyzer and indirectly with a detector that responded to the X-rays produced by electron impact on the target. At low currents the distribution is sharply peaked at the acceleration potential. At high currents a beam plasma discharge occurs and electrons are redistributed in energy so that the former energy peak broadens to 10-15 percent FWHM with a strongly enhanced low energy tail. At the 10% of maximum point the energy spectrum ranges from less than 1/2 to 1.2 times the gun energy. The effect is qualitatively the same at all pitch angles and locations sampled.

Jost, R. J.↗
DOE OSTI2022

Snowmass2021 Topical Group Report from AF07: Targets and Sources

For the next multi-megawatt accelerator generation, targets and other beam-intercepting components will face even more severe challenges due to the higher power densities, higher energy, and higher radiation. A comprehensive research and development program must be implemented to address the challenges. International collaborations such as RaDIATE or High Power Targetry Workshop should be leveraged and expanded to accelerate knowledge gain and avoid duplicated efforts. The next generation of high power targets will need novel designs allowing better high heat flux cooling methods, novel materials, advanced simulations, and better instrumentation. Four main R&D tracks were identified and discussed for targets. For electron sources, current state of art and challenges we are facing for key components such as cathodes, guns and injector design for sources R&D are presented for highly polarized electrons and unpolarized high current high brightness beams. For ion sources such as electron cyclotron resonance ion source (ECRIS), laser ion source (LIS), charge breeders, status of development are reviewed, and areas require investment for future R&D are discussed separately. Facilities critical for various source development are recommended.

43 PARTICLE ACCELERATORS↗
DOE OSTI2022

Photoemission characterization of N-polar III-nitride photocathodes as candidate bright electron beam sources for accelerator applications

We report on the growth and characterization of a new class of photocathode structures for use as electron sources to produce high brightness electron beams for accelerator applications. The sources are realized using III-nitride materials and are designed to leverage the strong polarization field, which is characteristic of this class of materials when grown in their wurtzite crystal structure, to produce a negative electron affinity condition without the use of Cs, possibly allowing these materials to be operated in radio frequency guns. A Quantum Efficiency (QE) of about 1×10−3 and an emitted electrons’ Mean Transverse Energy (MTE) of about 100 meV are measured at a wavelength of 265 nm. In a vacuum level of 3×10−10 Torr, the QE does not decrease after more than 24 h of continuous operation. The lowest MTE of about 50 meV is measured at 300 nm along with a QE of 1.5×10−5. Surface characterizations reveal a possible contribution to the MTE from surface morphology, calling for more detailed studies.

Cultrera, L. (ORCID:0000000235606059)↗
NASA NTRS1982

Characterization of advanced electric propulsion systems

Characteristics of several advanced electric propulsion systems are evaluated and compared. The propulsion systems studied are mass driver, rail gun, MPD thruster, hydrogen free radical thruster and mercury electron bombardment ion engine. These are characterized by specific impulse, overall efficiency, input power, average thrust, power to average thrust ratio and average thrust to dry weight ratio. Several important physical characteristics such as dry system mass, accelerator length, bore size and current pulse requirement are also evaluated in appropriate cases. Only the ion engine can operate at a specific impulse beyond 2000 sec. Rail gun, MPD thruster and free radical thruster are currently characterized by low efficiencies. Mass drivers have the best performance characteristics in terms of overall efficiency, power to average thrust ratio and average thrust to dry weight ratio. But, they can only operate at low specific impulses due to large power requirements and are extremely long due to limitations of driving current. Mercury ion engines have the next best performance characteristics while operating at higher specific impulses. It is concluded that, overall, ion engines have somewhat better characteristics as compared to the other electric propulsion systems.

Ray, P. K.↗
NASA NTRS1995

Propagation of beam-driven VLF waves from the ionosphere toward the ground

As part of the Cooperative High Altitude Rocket Gun Experiment (CHARGE-2B) rocket mission, an electron beam was injected into the ionosphere with a modulated beam current in an effort to generate very low frequency (VLF) waves. The propagation of the beam-driven VLF waves through the ionosphere is examined here to determine whether it is possible to detect these wave emissions with ground receivers. The paths of the VLF waves from where they were generated near the rocket were followed to the bottom of the ionosphere and the decrease in wave amplitude due to wave-particle resonance and collisional damping was calculated. It was found that due to collisional damping, which for these VLF waves becomes large at altitudes below about 150 km, wave amplitudes were decreased below the background atmospheric noise level. A number of different beam injection events have been examined and in all of these cases studied the waves were sufficiently damped such that detection on the ground would not be possible. This is in agreement with observations on the ground in which no wave emissions were observed during the CHARGE-2B mission. Control parameters that would be more favorable for beam-generated VLF propagation to the ground are discussed for future experiments of this type.

Schriver, David↗
NASA NTRS1973

In situ sputter cleaning of thin film metal substrates for UHV-TEM corrosion studies.

A prerequisite for conducting valid corrosion experiments by in situ electron microscopy techniques is not only the achievement of UHV background pressure conditions at the site of the specimen but also the ability to clean the surface of the thin metal substrate specimen before initiation of the corrosive interaction. A miniaturized simple ion gun has been constructed for this purpose. The gun is small enough to be incorporated into an UHV electron microscope specimen chamber with hot stage in such a way as to permit bombardment of the substrate specimen while observing it by transmission electron microscopy TEM. It is shown that the ion beam generated is confined well enough to cause a sputtering removal of substrate material at a rate of approximately 5-10 A/min and to prevent the sputter deposition of contaminating material from the specimen holder.

Heinemann, K.↗
DOE OSTI2024

Muon-induced baryon number violation

The search for charged-lepton flavor violation in muon capture on nuclei is a powerful probe of heavy new physics. A smoking gun signal for μ → e conversion is a monochromatic electron with energy almost equal to the muon mass. We show that light new physics can mimic this signature and that it can also lead to electrons above the μ → e signal peak. A concrete example of such light new physics is μ − -nucleon annihilation into a light dark sector, which can produce an energetic e − as well as e + e − by-products. Due to the size of the muon mass, the exotic muon capture process can be kinematically allowed, while the otherwise stringent constraints, e.g., from proton decay, are kinematically forbidden. We also discuss other relevant constraints, including those from the stability of nuclei and muon capture in the interior of neutron stars. Published by the American Physical Society 2024

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS1985

Heavy ion beam-ionosphere interactions - Electron acceleration

Moore et al. (1982) described a number of unexpected effects which were observed during the first Argon Release Controlled Study (ARCS 1, or rocket flight 29:014). The present paper provides a description of detailed analyses of the interaction of the argon beam with the ionosphere. An important feature of the considered test was that all detectors and the Ar(+) gun remained attached to the rocket throughout the flight. It is pointed out that the most dramatic effect of ion gun operation on ARCS 1 involved large changes in the fluxes of electrons with energies below about 600 eV. The observations are discussed, taking into account the distribution functions, azimuth dependence, and electron and ion trajectories. Attention is given to the perpendicular ion beam, the parallel ion beam, the acceleration of downgoing and upgoing electrons, and aspects of wave generation.

Kaufmann, R. L.↗
NASA NTRS1978

Heating of the ambient ionosphere by an artificially injected electron beam

An electrostatic analyzer on the electron accelerator of the Electron Echo 2 experiment showed that the electrons of the background plasma were heated to 10,000 K or more within 8 ms of the start of gun pulses. The degree of heating was dependent on the orientation of the rocket with respect to the magnetic field but was not measurably dependent on ambient electron density, neutral atmosphere density, or on the pitch angle at which the 40-keV electron beam was injected. This heating was also accompanied by an increase of plasma density. No evidence was found for an ion-free region around the rocket during gun pulses. These observations show that significant amounts of ionization are taking place around the rocket. During part of the flight a two-temperature electron distribution was found. It is believed that the high-temperature part of these distributions represents secondaries produced by the beam.

Cartwright, D. G.↗
DOE OSTI2021

Cryogenic operation of planar ultrananocrystalline diamond field emission source in SRF injector

Here, we report a demonstration of electron beam generation in a superconducting radio frequency (SRF) Teraelectronvolt Energy Superconducting Linear Accelerator 1.3 GHz gun equipped with a field emission cathode and operated at 2 K. The cathode is a submicrometer film of nitrogen-incorporated ultrananocrystalline diamond [(N)UNCD] deposited atop a Nb RRR300 cathode plug that is 4 mm in diameter. Measurements of the output current showed that it increased exponentially as a function of the gun gradient. Our results demonstrate a feasible path toward simplified fully cryogenic SRF injector technology. At a maximal gradient of 0.9 MV/m, a current density of 22 μA/cm2 was obtained [calculated as a 2.75 μA current over the total cathode surface area of π(2 mm)2]. One important finding is that the electron emitter made of (N)UNCD, a material long been known as a highly efficient field emission material, demonstrated a record low turn-on gradient of 0.6 MV/m. A hypothesis explaining this behavior is proposed.

43 PARTICLE ACCELERATORS↗
DOE OSTI2021

Shock-reshock of zirconium to explore the effect of microstructure on the alpha-omega phase transformation

Phase transformations play an important role in the mechanical behavior of materials subjected to extreme loading conditions. A series of shock-reshock experiments were fielded to determine whether the phase transitions in materials are significantly enhanced or inhibited by preexisting microstructural features. Polycrystalline zirconium samples were shock loaded using gas-gun plate impact and soft recovered to examine microstructure using electron backscatter diffraction (EBSD). Drive conditions were varied to study the (hcp) alpha to (hexagonal) omega solidsolid phase transformation. Recovered samples were then subjected to a second shock loading event to determine the change in material behavior as a function of pre-shock microstructure. Crystallography of phase fragments in the final microstructure showed that prior twinning (formed during the shock to a peak stress below the transition threshold) appeared to suppress omega formation/retention after reshock. Conversely, when a material was initially shocked into the omega phase field, retained-omega was not found to have a large impact on subsequent omega formation during reshock. This suggests that nucleation and growth of omega phase are important processes, and the relative activity of nucleation vs. growth processes is modified by a pre-existing substructure. Additionally, orientation relationships reveal a reverse transformation pathway (omega to alpha) dominates the final microstructure, suggesting significant grain growth in the omega phase field is possible even for dynamic timescales.

36 MATERIALS SCIENCE↗