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DOE OSTI2021

Collaborative Research: Explosive reconnection in relativistic magnetically-dominated plasmas (Final Report)

Magnetic fields can be the dominant component of astrophysical plasmas, so that the magnetic energy density might exceed even the rest-mass energy density of matter. In this extreme (and largely unexplored) regime the magnetic field controls the overall plasma evolution, dissipation, and acceleration of non-thermal particles. This plasma regime, applicable to a variety of astrophysical sources - magnetars, pulsars and pulsar wind nebulae (PWNe), jets of Active Galactic Nuclei (AGNs) and Gamma-Ray Bursters (GRBs) - is dramatically different from laboratory plasmas, the magnetospheres of planets, and the interplanetary plasma. Relativistic astrophysical sources then provide an unique opportunity to study the fundamental plasma physics of magnetically-dominated plasmas; a novel and fast-evolving field of theoretical research which, by investigating energy conversion and particle energization processes in plasmas, is of vital importance to the Fusion Energy Sciences DoE program. Data coming from astrophysical high-energy missions, especially the Crab Nebula flares recently observed by the Fermi and AGILE satellites, suggest that the acceleration of non-thermal particles to the highest energies occurs in magnetic reconnection events - a major change of paradigm in high-energy astrophysics. Most importantly, observations demand that particle acceleration should proceed extremely fast (with accelerating electric field of the order of the magnetic field) and on macroscopic scales (much larger, e.g., than the microscopic plasma skin depth). We are conducting studies of the microphysics of magnetically-dominated plasmas focussing in particular on the highly dynamic regime of explosive reconnection and associated particle acceleration in relativistic plasmas. We are studying the stability and explosive plasma dynamics, particle acceleration and radiation production in a number of idealized plasma configurations that approximate relevant astrophysical sources (like the magnetic ABC structures and interacting flux tubes, as well as generalizations of analytical models of X-point collapse to relativistic plasmas). The well-studied case of the Crab Nebula is taken as a prototypical example for the application of the model. We are combining analytical studies of explosive magnetic dynamics and dissipation in relativistic plasmas with particle-in-cell (PIC) simulations and fluid simulations. The theoretical model, fluid and particle-in-cell simulations are cross-checked for agreement and convergence.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

NASA NTRS1976

Thermal testing of a high powered communications satellite

Thermal Vacuum and Thermal Balance tests were successfully conducted on the high power Communications Technology Satellite (CTS). The mission required testing for two distinct thermal environments; spin stabilized at 60 rpm with a minimum of 55 watts of dissipated power, and three-axis stabilized with as much as a tenfold increase of dissipation. The test program verified the adequacy of the spacecraft thermal design and demonstrated functional operation over a wide temperature range for all of the components. Special test hardware incorporating water-cooling systems was required to accomodate the heatpipes and high RF output power. Objectives, test facilities, special hardware, spacecraft configurations, and results of the tests are discussed. Preliminary flight results and conclusions drawn from the test experience are reported.

Caswell, R. D.↗

DOE OSTI2024

Spin-caloric resistance of Dirac plasma in a graphene Corbino device

The thermal resistance of a spin-polarized hydrodynamic Dirac plasma in graphene is considered. Here, a mechanism for the coupling of heat and spin flows is discussed, demonstrating that spin diffusion and spin thermocurrent modify viscous dissipation, leading to a significant enhancement of thermal resistance. Practical calculations are then presented for graphene devices in the Corbino geometry.

Graphene↗

NASA NTRSDate not supplied

Thermal Analysis of NRHO Entry Lunar Flyby Maneuver

NASA’s Gateway will serve as a platform for sustained human lunar exploration and an opportunity to gain experience with long duration deep-space architectures. The first two Gateway modules, the Power and Propulsion Element (PPE) and the Habitation and Logistics Outpost (HALO) are scheduled to launch together as a Co-Manifested Vehicle (CMV) in 2024. To reach the destination Near-Rectilinear Halo Orbit (NRHO), the CMV will perform a low-thrust electric propulsion spiral and a final transfer maneuver that will include a low altitude flyby of the lunar surface. This flyby thermal environment is more adverse than that expected during the NRHO itself and risks temperature exceedances on various spacecraft components. The highly transient nature of the flyby also required a different approach than the typical worst-case dissipation margins used to size the spacecraft thermal control systems. This paper presents analyses on the relative severity of different minimum perilune altitudes and results of an integrated CMV thermal model built in Thermal Desktop.

lunar flyby maneuver↗

DOE OSTI2020

Heat Generation versus Heat Dissipation Maps for Batteries (Battery Safety Maps) [SWR-21-27]

NREL's Battery Safety Map (Heat Generation versus Heat Dissipation Maps for Batteries) generates a response surface that is grouped into regions where the battery is deemed safe from the propagation of thermal runaway, those where an engineering solution would render the battery safe, and finally instances where thermal runaway is inevitable. The demarcation for the different regions is provided by specifications or constraints imposed by the end user. NREL's Battery Safety Map is a user-defined subroutine that sweeps through a set of parameters describing the operating conditions and short-circuit scenarios for battery safety simulations. For each run, the electrochemical-thermal model implementing reaction kinetics and gas generation are run to evaluate the amount of heat generated. A thermal model then captures the amount of heat dissipation based on boundary conditions defined (e.g., forced convection, constant temperature at the surface, etc.). Based on the rate of heat transfer and the amount of heat generated, each run is classified into "safe," "mitigation possible," or "unsafe" zones. These categories are defined based on constraints or tolerance specifications provided by the end user.

Santhanagopalan, Shriram↗

NASA NTRS2017

Thermal Modeling of Mars Ground for Surface Missions

Thermal analysis packages are capable of including ground temperature effects for orbital and surface thermal analyses. In particular, Thermal Desktop® offers the option of specifying ground temperatures as a function of time for planetary surface modeling. While suitable for many cases, this approach is not sufficient if an object has local interactions with the ground that could significantly affect the ground temperature. Ground modeling is necessary for the Mars 2020 rover thermal design and analysis since shadowing and heat dissipation from the rover’s Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) can result in significant temperature deviations of the local ground. The Mars 2020 thermal team is explicitly modeling the Martian ground so that these local temperature effects can be captured. The upper portion of the ground is modeled, and material and optical properties of the ground are varied in order to match data collected from orbiting science instruments. Atmospheric surface temperature, sky temperatures, and solar loads from a Mars General Circulation Model (GCM) are used as boundary conditions, resulting in a ground surface temperature profile consistent with the GCM predictions. The rover model is then placed on this modeled ground so that the effects of shadowing and MMRTG dissipation on the ground temperature can be captured.

Farias, Edgardo↗

DOE OSTI2020

As a Matter of State: The Role of Thermodynamics in Magnetohydrodynamic Turbulence

Turbulence simulations play a key role in advancing the general understanding of the physical properties of turbulence and in interpreting astrophysical observations of turbulent plasmas. For the sake of simplicity, however, turbulence simulations are often conducted in the isothermal limit. Given that the majority of astrophysical systems are not governed by isothermal dynamics, we aim to quantify the impact of thermodynamics on the physics of turbulence, through varying adiabatic index, γ, combined with a range of optically thin cooling functions. Here, we present a suite of ideal magnetohydrodynamics simulations of thermally balanced stationary turbulence in the subsonic, super-Alfvénic, high ${\beta }_{{\rm{p}}}$ (ratio of thermal to magnetic pressure) regime, where turbulent dissipation is balanced by two idealized cooling functions (approximating linear cooling and free–free emission) and examine the impact of the equation of state by considering cases that correspond to isothermal, monatomic, and diatomic gases. We find a strong anticorrelation between thermal and magnetic pressure independent of thermodynamics, whereas the strong anticorrelation between density and magnetic field found in the isothermal case weakens with increasing γ. Similarly, the linear relation between variations in density and thermal pressure with sonic Mach number becomes steeper with increasing γ. This suggests that there exists a degeneracy in these relations with respect to thermodynamics and Mach number in this regime, which is dominated by slow magnetosonic modes. These results have implications for attempts to infer (e.g.,) Mach numbers from (e.g.,) Faraday rotation measurements, without additional information regarding the thermodynamics of the plasma. However, our results suggest that this degeneracy can be broken by utilizing higher-order moments of observable distribution functions.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2022

In-situ irradiation-induced studies of grain growth kinetics of nanocrystalline UO 2

The thermal conductivity of UO 2 fuel needs to be high enough to dissipate the heat generated from the fission reaction. Since grain size affects thermal conductivity and grain size can evolve with irradiation, it is critical to understand in-reactor UO 2 grain growth. Most studies of grain growth in UO 2 are based on thermally driven processes at elevated temperatures. However, studies have shown that grain growth can occur even at cryogenic temperatures by ballistic processes. Such irradiation-induced grain growth in UO 2 is yet to be studied. Advanced in-situ Kr ion irradiation and transmission electron microscopy were systematically performed on nanocrystalline UO 2 thin films at temperatures ranging from 50 K to 1073 K; grain growth was observed at all temperatures. A combination of manual and machine learning techniques was used to measure and plot grain size evolution against irradiation fluence at various irradiation temperatures. The machine learning method has significantly improved the analysis efficiency and reduced human labors. The grain diameter data were fitted using classical grain growth and thermal spike models to describe grain growth kinetics with and without irradiation effect. Grain growth during low temperature irradiation (≤ 475 K) can be well described by the thermal spike model. Above 475 K, there were additional thermally assisted processes that further accelerate the grain growth. At the highest irradiation temperature about 1075 K, both irradiation-induced dislocation loops and cavities/bubbles were observed to form in the UO 2 . In this report, the effects of irradiation-induced defects on grain growth kinetics are discussed.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

DOE OSTI2023

Isothermal Microcalorimetric Analysis of Li/CF x Battery Discharge

Lithium/carbon monofluoride (Li/CF x ) batteries generate substantial amounts of heat during discharge in part due to the large deviation of the loaded voltage from the measured and thermodynamically predicted open circuit voltage. Here, in this study, we further analyze this system by estimating the equilibrium voltage (V eq ) and its temperature dependence (dV eq /dT) over the entire discharge range. Based on these results, the ohmic and entropic heat contributions to the overall heat flow are calculated from experimental data. The ohmic heat flow is consistent with an electrochemical impedance spectroscopy model and electrode density measurements, indicating decreasing porosity of the electrode during discharge. Entropic heating increases during discharge as the cell reaction becomes increasingly entropically unfavorable. The total energy dissipated by the cell (electrical and thermal) remains similar over the entire discharge, evidence for a two-phase reaction with a constant, and rate-independent, ΔG rxn of about -465 kJ mol -1 . However, near the end of discharge (>90% DOD), ΔG rxn changes significantly indicating possible secondary reactions.

25 ENERGY STORAGE↗

DOE OSTI2022

Collaborative Research: Explosive reconnection in relativistic magnetically-dominated plasmas

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1965

Electropneumatic rheostat regulates high current

Electropneumatic rheostat maintains a constant direct current in each of several high-power parallel loads, of variable resistance, across a single source. It provides current regulation at any preset value by dissipating the proper amount of energy thermally, and uses a column of mercury to vary the effective length of a resistance element.

Haacker, J. F.↗

NASA NTRS1981

Thermionic Energy Conversion (TEC) topping thermoelectrics

Performance expectations for thermionic and thermoelectric energy conversion systems are reviewed. It is noted that internal radiation effects diminish thermoelectric figures of merit significantly at 1000 K and substantially at 2000 K; the effective thermal conductivity contribution of intrathermoelectric radiative dissipation increases with the third power of temperature. It is argued that a consideration of thermoelectric power generation with high temperature heat sources should include utilization of thermionic energy conversion (TEC) topping thermoelectrics. However TEC alone or TEC topping more efficient conversion systems like steam or gas turbines, combined cycles, or Stirling engines would be more desirable generally.

Morris, J. F.↗

NASA NTRS1980

Second quadrant effects in silicon solar cells

A simple model describing the behavior of a solar cell in the second quadrant of the I-V curve is described. In this mode of operation appreciable power is dissipated in the cell leading to thermal breakdown and the formation of hot spots. These hot spots will be stable in a current limited mode of operation. In addition a simple method is described to locate the hot spots.

Hartman, R. A.↗

NASA NTRS1987

Frequency stabilization in injection controlled pulsed CO2 lasers

Longitudinal mode selection by injection has been demonstrated as a viable technique for tailoring a TEA-CO2 laser with pulse energies of a Joule or greater to fit the requirements of a coherent lidar transmitter. Once reliable generation of single-longitudinal-mode (SLM) pulses is obtained, one can study the intrapulse frequency variation and attempt to determine the sources of frequency sweeping, or chirp. These sources include the effect of the decaying plasma, the thermal gradient due to the energy dissipation associated with the laser mechanism itself, and the pressure shift of the center frequency of the laser transition. The use of the positive-branch unstable resonator as an efficient means of coupling a discharge with transverse spatial dimensions of the order of centimeters to an optical cavity mode introduces another concern: namely, what can be done to emphasize transverse mode discrimination in an unstable resonator cavity while maintaining high coupling efficiency. These issues are briefly discussed in the paper, and representative experimental examples are included.

Menzies, Robert T.↗

NASA NTRS1987

Frequency stabilization and transverse mode discrimination in injection-seeded unstable resonator TEA CO2 lasers

Longitudinal mode selection by injection has been demonstrated as a viable technique for TEA-CO2 lasers with pulse energies of a Joule or greater. Once reliable generation of single-longitudinal-mode (SLM) pulses is obtained, the characteristics and the causes of intrapulse frequency variation can be studied. These include the effect of the decaying plasma, the thermal gradient due to the energy dissipation associated with the laser mechanism itself, and the pressure shift of the center frequency of the laser transition. The use of the positive-branch unstable resonator as an efficient means of coupling a discharge with large spatial dimensions to an optical cavity mode introduces another concern: namely, what can be done to emphasize transverse mode discrimination in an unstable resonator cavity while maintaining high coupling efficiency. These issues are discussed in this paper, and relevant experimental results are included.

Ancellet, G. M.↗

NASA NTRS1989

Discrete events and solar wind energization

Based on a multiple-magnetic-reconnection picture, an estimation of the energy flux suggests that small-scale EUV exploding events may contribute a significant amount of energy (of order of 100,000 erg/sq cm sec) to solar atmospheric heating and solar-wind acceleration. Most of the dissipated magnetic energy is converted into thermal energy and plasma turbulence. On a related aspect, a numerical study based on the nonlinear one-fluid hydrodynamic equations shows a self-smoothing effect, whereby a multistream structure of the solar wind formed near the sun can be gradually smoothed during its propagation through interplanetary space. This calculation gives support for the possible contribution of discrete energetic events to high-speed solar wind streams.

Yang, W.-H.↗

NASA NTRS1992

Analysis of Voyager 2 images of Jovian lightning

Magalhaes and Borucki (1991) reported that Voyager-2 images of Jupiter contained bright spots due to lightning activity that was confined to two narrow altitude bands centered at 49 deg N and 13.5 deg N latitude and to a single region near 60 deg N latitude. This paper describes the Voyager 2 imaging observations in detail and associates the positions of the lightning features in the images with particular cloud features. The energetics of the lightning storms on Jupiter is examined. It is found that the ratio of the energy dissipated by Jovian lightning to the thermal flux available to drive convection motions is about 3 decades larger than the terrestrial ratio.

Borucki, William J.↗

NASA NTRS1995

The Geopause

Coupled to the Earth and protected by the geomagnetic field, terrestrial matter in the plasma state dominates a larger region of space than was suspected when the 'space age' began, a region we refer to as the geosphere. Accelerated and heated by solar wind energy, this matter expands in size and increases in mass density in response to the Sun's ultraviolet spectrum, heliospheric conditions, and the occurrence of severe space storms. Such storms regularly damage spacecraft, interfere with communications, and trigger power grid interruptions or failures. They occur within the geopause region, that is, the volume defined by the limits of the instantaneous boundary between plasmas that are primarily heliospheric and geospheric. The geopause is analogous in some ways to the heliopause but also resembles the terrestrial air-sea interface. It is the boundary layer across which the supersonically expanding solar plasma delivers momentum and energy to the terrestrial plasma and gas, exciting them into motion, 'evaporating' them into space, and dissipating considerable amounts of power in thermal forms, while generating energetic particles through repeated storage and explosive release of electromagnetic energy. The intensity of the solar wind and the orientation of its magnetic field jointly control the strength of the coupling between solar and terrestrial plasmas and hence the occurrence of severe storms in the geopause region.

Moore, T. E.↗