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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 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Passive Two-Phase Cooling of Automotive Power Electronics: Preprint

Experiments were conducted to evaluate the use of a passive two-phase cooling strategy as a means of cooling automotive power electronics. The proposed cooling approach utilizes an indirect cooling configuration to alleviate some reliability concerns and to allow the use of conventional power modules. An inverter-scale proof-of-concept cooling system was fabricated, and tests were conducted using the refrigerants hydrofluoroolefin HFO-1234yf and hydrofluorocarbon HFC-245fa. Results demonstrated that the system can dissipate at least 3.5 kW of heat with 250 cm3 of HFC-245fa. An advanced evaporator design that incorporates features to improve performance and reduce size was conceived. Simulation results indicate its thermal resistance can be 37% to 48% lower than automotive dual side cooled power modules. Tests were also conducted to measure the thermal performance of two air-cooled condensers--plain and rifled finned tube designs. The results combined with some analysis were then used to estimate the required condenser size per operating conditions and maximum allowable system (i.e., vapor and liquid) temperatures.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2024

Numerical modeling of a proof-of-principle experiment on optical stochastic cooling at an electron storage ring

Cooling of beams circulating in storage rings is critical for many applications including particle colliders and synchrotron light sources. A method enabling unprecedented beam-cooling rates, optical stochastic cooling (OSC), was recently demonstrated in the Integrable Optics Test Accelerator (IOTA) electron storage ring at Fermilab [J. Jarvis , ]. This paper describes the numerical implementation of the OSC process in the particle-tracking program and discusses the validation of the developed model with available experimental data. The model is also employed to highlight some features associated with different modes of operation of OSC. The developed simulation tool should be valuable in guiding future configurations of optical stochastic cooling and, more broadly, modeling self-field-based beam manipulations. Published by the American Physical Society 2024

43 PARTICLE ACCELERATORS↗
DOE OSTI2024

Intrinsically Slow Cooling of Hot Electrons in CdSe Nanocrystals Compared to CdS

The utilization of excited charge carriers in semiconductor nanocrystals (NCs) for optoelectronic technologies has been a long-standing goal in the field of nanoscience. Experimental efforts to extend the lifetime of excited carriers have therefore been a principal focus. To understand the limits of these lifetimes, in this work, we theoretically study the time scales of pure electron relaxation in negatively charged NCs composed of two prototypical materials: CdSe and CdS. We find that hot electrons in CdSe have lifetimes that are 5 to 6 orders of magnitude longer than in CdS when the relaxation is governed only by the intrinsic properties of the materials. Although these two materials are known to have somewhat different electronic structure, we elucidate how this enormous difference in lifetimes arises from relatively small quantitative differences in electronic energy gaps and phonon frequencies, as well as the crucial role of Fröhlich-type electron–phonon couplings.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2014

Ion acoustic solitary waves and double layers in a plasma with two temperature electrons featuring Tsallis distribution

The propagation properties of large amplitude ion acoustic solitary waves (IASWs) are studied in a plasma containing cold fluid ions and multi-temperature electrons (cool and hot electrons) with nonextensive distribution. Employing Sagdeev pseudopotential method, an energy balance equation has been derived and from the expression for Sagdeev potential function, ion acoustic solitary waves and double layers are investigated numerically. The Mach number (lower and upper limits) for the existence of solitary structures is determined. Positive as well as negative polarity solitary structures are observed. Further, conditions for the existence of ion acoustic double layers (IADLs) are also determined numerically in the form of the critical values of q{sub c}, f and the Mach number (M). It is observed that the nonextensivity of electrons (via q{sub c,h}), concentration of electrons (via f) and temperature ratio of cold to hot electrons (via β) significantly influence the characteristics of ion acoustic solitary waves as well as double layers.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Flow boiling in geometrically modified microchannels

Microchannels are a promising solution for high-heat-flux thermal management scenarios, including high-performance microelectronics cooling and power electronics cooling. However, thermohydraulic instabilities result from the rapid vapor bubble formation. The prior literature has examined several methods, including constricted inlet microchannels, expanding microchannels, and auxiliary jetting microchannels, to mitigate the effect of these instabilities. Computational fluid dynamics and heat transfer (CFD/HT) modeling of the flow boiling phenomena in these microchannel configurations has seen limited examination, and one-to-one numerical comparisons of the different mitigation strategies have not been performed. In the present investigation, CFD/HT analyses using a three-dimensional (3D) volume of fluid model coupled with a phase-change model for the interfacial heat and mass transfer were performed for multiple microchannel configurations (constricted inlet, expanding, and auxiliary jetting microchannels). A benchmark case of a rectangular microchannel was examined to quantify baseline thermohydraulic performance. Results demonstrated slight to significant thermal performance improvements for all cases, and significant pressure benefits for the expanding and jetting cases, consistent with experimental results in the literature. Bubble dynamics and visualization for the baseline and alternative configurations are provided to give insight into their underlying physics, and the differences in performance were investigated and compared with available literature.

Broughton, Justin (ORCID:000000026848457X)↗
DOE OSTI2015

Commissioning of the 112 MHz SRF Gun and 500 MHz bunching cavities for the CeC PoP Linac

The Coherent electron Cooling Proof-of-Principle (CeC PoP) experiment at BNL includes a short electron linac. During Phase 1, a 112 MHz superconducting RF photo-emission gun and two 500 MHz normal conducting bunching cavities were installed and are under commissioning. The paper describes the Phase1 linac layout and presents commissioning results for the cavities and associated RF, cryogenic and other sub-systems

43 PARTICLE ACCELERATORS↗
DOE OSTI2016

Report on LEReC Recombination Monitor APEX Study on June 15th 2016

During the prospective Low Energy RHIC electron Cooling (LEReC) operation, the electron beam will overlap and interact with the low energy ion beam to provide transverse cooling. Cooling is needed to facilitate reaching the BES-2 (Beam Energy Scan 2) program goals of an average store luminosity of 5 × 10 24 cm -2 s -1 at 3.85 GeV/n and 17.3 × 10 24 cm -2 s -1 at 9.1 GeV/n. The RHIC phase of BES-2 is currently planned for the RHIC runs in 2019 and 2020. Effective cooling will depend on the accuracy of velocity matching between the two beams. Another process, the rate of ion-electron recombination, is also maximized when the velocities are matched, but the exact matching requirement is less stringent. Therefore, as suggested by one of us, detecting and maximizing recombination signals should be helpful in finding the narrow velocity matching window conducive to cooling. When 197 Au 79+ RHIC ions pick up an electron from the LEREeC electron beam they are converted into 197 Au 78+ ions with nearly the same momentum while having about 1.3% higher magnetic rigidity than the original 197 Au 79+ particles. The detection of the recombined ions can be done by driving the 197 Au 78+ beam into the beam pipe wall, creating showers of secondary particles which then can be detected outside the cryostat by using appropriately positioned detectors. For the purpose of forcing losses of the expected off-momentum particles a dedicated lattice with large horizontal dispersion in one arc was proposed and designed.

43 PARTICLE ACCELERATORS↗
NASA NTRS2015

Heat Capacity and Thermal Conductance Measurements of a Superconducting-Normal Mixed State by Detection of Single 3 eV Photons in a Magnetic Penetration Thermometer

We report on measurements of the detected signal pulses in a molybdenum-gold Magnetic Penetration Thermometer (MPT) in response to absorption of one or more 3 eV photons. We designed and used this MPT sensor for x-ray microcalorimetry. In this device, the diamagnetic response of a superconducting MoAu bilayer is used to sense temperature changes in response to absorbed photons, and responsivity is enhanced by a Meissner transition in which the magnetic flux penetrating the sensor changes rapidly to minimize free energy in a mixed superconducting normal state. We have previously reported on use of our MPT to study a thermal phonon energy loss to the substrate when absorbing x-rays. We now describe results of extracting heat capacity C and thermal conductance G values from pulse height and decay time of MPT pulses generated by 3 eV photons. The variation in C and G at temperatures near the Meissner transition temperature (set by an internal magnetic bias field) allow us to probe the behavior in superconducting normal mixed state of the condensation energy and the electron cooling power resulting from quasi-particle recombination and phonon emission. The information gained on electron cooling power is also relevant to the operation of other superconducting detectors, such as Microwave Kinetic Inductance Detectors.

superconductivity↗
DOE OSTI2021

Summary of the CeC Experiment in RHIC Run 21

The coherent electron cooling (CeC) experiment at RHIC is crucial for determining the feasibility of this technique for cooling the hadron beam in the electron-ion collider (EIC) and reaching the luminosity of 10 34 cm -1 s -1 . During RHIC Run 21, various progresses have been made including successfully commissioning the time resolved diagnostic beam line (TRDBL), achieving the key performance parameters (KPP) of the system and the development of novel methods for accurate alignment of the electron beam with the ion beam. While the longitudinal cooling of the ion beam with cooling time of 100 hours was observed during Run 21, it was related to the traditional electron cooling since the cooling rate was not as sensitive to the energy of the electron beam as what one would expect from the CeC. In Run 21, we were not able to observe the longitudinal cooling of the ion beam caused by CeC and the main challenges are identified as the insufficient stability of the electrons' energy. The sources of the energy jitter have been identified and we are making improvements to the stability of the CeC system for Run 22.

43 PARTICLE ACCELERATORS↗
DOE OSTI2017

Giant increase in cross-magnetic-field transport rate as an electron-positron plasma cools

An electron-positron plasma in thermal equilibrium within a uniform magnetic field is studied here using a classical trajectory Monte Carlo simulation. The cross-magnetic-field single-particle diffusion coefficient is evaluated as a function of the magnetic field strength and plasma temperature. The transport rate is found to increase by many orders of magnitude as the plasma temperature is lowered, for a magnetic field strength of 1 T. The sharp dependence on temperature is due to electrons and positrons becoming temporarily correlated and drifting across the magnetic field before dissociating.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Experimental Demonstration of Hadron Beam Cooling Using Radio-Frequency Accelerated Electron Bunches

Cooling of beams of gold ions using electron bunches accelerated with radio-frequency systems was recently experimentally demonstrated in the Relativistic Heavy Ion Collider at Brookhaven National Laboratory. Such an approach is new and opens the possibility of using this technique at higher energies than possible with electrostatic acceleration of electron beams. The challenges of this approach include generation of electron beams suitable for cooling, delivery of electron bunches of the required quality to the cooling sections without degradation of beam angular divergence and energy spread, achieving the required small angles between electron and ion trajectories in the cooling sections, precise velocity matching between the two beams, high-current operation of the electron accelerator, as well as several physics effects related to bunched-beam cooling. Here we report on the first demonstration of cooling hadron beams using this new approach.

43 PARTICLE ACCELERATORS↗
DOE OSTI2015

Analysis of FEL-based CeC amplification at high gain limit

An analysis of Coherent electron Cooling (CeC) amplifier based on 1D Free Electron Laser (FEL) theory was previously performed with exact solution of the dispersion relation, assuming electrons having Lorentzian energy distribution. At high gain limit, the asymptotic behavior of the FEL amplifier can be better understood by Taylor expanding the exact solution of the dispersion relation with respect to the detuning parameter. In this work, we make quadratic expansion of the dispersion relation for Lorentzian energy distribution and investigate how longitudinal space charge and electrons’ energy spread affect the FEL amplification process.

43 PARTICLE ACCELERATORS↗
DOE OSTI2016

Communication: Uncovering correlated vibrational cooling and electron transfer dynamics with multidimensional spectroscopy

Analogues of 2D photon echo methods in which two population times are sampled have recently been used to expose heterogeneity in chemical kinetics. In this work, the two population times sampled for a transition metal complex are transformed into a 2D rate spectrum using the maximum entropy method. The 2D rate spectrum suggests heterogeneity in the vibrational cooling (VC) rate within the ensemble. In addition, a cross peak associated with VC and back electron transfer (BET) dynamics reveals correlation between the two processes. Here, we hypothesize that an increase in the strength of solute-solvent interactions, which accelerates VC, drives the system toward the activationless regime of BET.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Screening of hot electrons in the ferroelectric semiconductor In 2 Se 3

We report that in a conventional semiconductor, electrons (e) scatter efficiently with longitudinal-optical phonons (ph LO ) via the Fröhlich interaction, e.g., in polaron formation or hot-electron cooling. Recent studies on lead halide perovskites have suggested that the Fröhlich interaction may be sufficiently screened by the polar lattice. Here we show that hot-electron cooling in a layered ferroelectric semiconductor In 2 Se 3 slows down by 50% as temperature is increased from 115 to 387 K; this decrease is about four times more than that predicted by the Fröhlich model. We suggest that screening of Fröhlich interaction by polar domains or fluctuations in the ferroelectric semiconductor may be responsible for the reduced e-ph LO scattering. Such enhanced screening in polar materials featuring anharmonic lattice instability may also reduce carrier scattering with other charge carriers or with charged defects, leading to improved optoelectronic properties.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Update on the CeC PoP 704 MHz 5-cell cavity cryomodule design and fabrication

A 5-cell SRF cavity operating at 704 MHz will be used for the Coherent Electron Cooling Proof of Principle (CeC PoP) system under development for the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory. The CeC PoP experiment will demonstrate the new technique of cooling proton and ion beams that may increase the beam luminosity in certain cases, by as much as tenfold. The 704 MHz cavity will accelerate 2 MeV electrons from a 112 MHz SRF gun up to 22MeV. This paper provides an overview of the design, the project status and schedule of the 704 MHz 5-cell SRF for CeC PoP experiment.

43 PARTICLE ACCELERATORS↗
DOE OSTI2021

3D Theoretical and simulation tools for microbunched cooling

The concept of microbunched electron cooling (MBEC, introduced in Ref. [1]) is currently under investigation as a candidate for the strong hadron cooling (SHC) component of EIC. Most of the theoretical treatments of this scheme are based on a simplified model for the longitudinal space charge [2–4]. In this model, the particle beams are treated as collections of thin charged disks, with the interaction function for two such disks being calculated by averaging the forces between constituent point charges. Although the disk model is flexible and captures a large part of the underlying physics, it lacks the fidelity and robustness of an analysis that explicitly treats the beams as collections of point charges. In what follows, we explore such a model, both from a theory-based and a simulation perspective.

43 PARTICLE ACCELERATORS↗
NASA NTRS1976

New fine structure cooling rate

One of the dominant electron cooling processes in the ionosphere is caused by electron impact induced fine structure transitions among the ground state levels of atomic oxygen. This fine structure cooling rate is based on theoretical cross sections. Recent advances in the numerical cross section determinations to include polarization effects and more accurate representations of the atomic target result in new lower values. These cross sections are employed in this paper to derive a new fine structure cooling rate which is between 40% and 60% of the currently used rate. A new generalized formula is presented for the cooling rate (from which the fine structure cooling rate is derived), valid for arbitrary mass and temperature difference of the colliding particles and arbitrary inelastic energy difference.

Hoegy, W. R.↗