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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 469 records · Page 26
All sourcesNASA NTRSDOE OSTI
NASA NTRS2012

Pulsar Polar Cap and Slot Gap Models: Confronting Fermi Data

Rotation-powered pulsars are excellent laboratories for studying particle acceleration as well as fundamental physics of strong gravity, strong magnetic fields and relativity. I will review acceleration and gamma-ray emission from the pulsar polar cap and slot gap. Predictions of these models can be tested with the data set on pulsars collected by the Large Area Telescope on the Fermi Gamma-Ray Telescope over the last four years, using both detailed light curve fitting and population synthesis.

Harding, Alice K.↗
NASA NTRS2012

Rotation Rate of Saturn's Magnetosphere using CAPS Plasma Measurements

We present the present status of an investigation of the rotation rate of Saturn 's magnetosphere using a 3D velocity moment technique being developed at Goddard which is similar to the 2D version used by Sittler et al. (2005) [1] for SOI and similar to that used by Thomsen et al. (2010). This technique allows one to nearly cover the full energy range of the CAPS IMS from 1 V less than or equal to E/Q less than 50 kV. Since our technique maps the observations into a local inertial frame, it does work during roll manoeuvres. We have made comparisons with Wilson et al. (2008) [2] (2005-358 and 2005-284) who performs a bi-Maxwellian fit to the ion singles data and our results are nearly identical. We will also make comparisons with results by Thomsen et al. (2010) [3]. Our analysis uses ion composition data to weight the non-compositional data, referred to as singles data, to separate H+, H2+ and water group ions (W+) from each other. The ion data set is especially valuable for measuring flow velocities for protons, which are more difficult to derive using singles data within the inner magnetosphere, where the signal is dominated by heavy ions (i.e., proton peak merges with W+ peak as low energy shoulder). Our technique uses a flux function, which is zero in the proper plasma flow frame, to estimate fluid parameter uncertainties. The comparisons investigate the experimental errors and potential for systematic errors in the analyses, including ours. The rolls provide the best data set when it comes to getting 4PI coverage of the plasma but are more susceptible to time aliasing effects. Since our analysis is a velocity moments technique it will work within the inner magnetosphere where pickup ions are important and velocity distributions are non-Maxwellian. So, we will present results inside Enceladus' L shell and determine if mass loading is important. In the future we plan to make comparisons with magnetic field observations, use Saturn ionosphere conductivities as presently known and the field aligned currents necessary for the planet to enforce corotation of the rotating plasma.

Sittler, E.↗
NASA NTRS2014

Titan's Plasma Environment : 3D Hybrid Kinetic Modeling of the TA Flyby and Comparison with CAPS-ELS and RPWS LP Observations

In this report we discuss the global plasma environment of the TA flyby from the perspective of 3D hybrid modeling. In our model the background, pickup, and ionospheric ions are considered as particles, whereas the electrons are described as a fluid. In homogeneous photoionization, electron-impact ionization and charge exchange are included in our model. We also take into account the collisions between the ions and neutrals. Our modeling shows that mass loading of the background plasma (H(+), O(+)) by pick up ions H2(+), CH4(+) and N2(+) differs from theT9 encounter simulations when O(+) ions are not introduced into the background plasma. In our hybrid-modeling we use Chamberlain profiles for the atmospheric components. We also include a simple ionosphere model with average mass M=28 amu ions that were generated inside the ionosphere. Titan's interior is considered as a weakly conducting body. Special attention has been paid to comparing the simulated pickup ion density distribution with CAPS-ELS and with RPWS LP observations by the Cassini-Huygens spacecraft along theta trajectory. Our modeling shows an asymmetry of the ion density distribution and the magnetic field, including the formation of Alfven wing-like structures.

induced magnetospheres↗
NASA NTRS2019

Formation of the Potential Jump over the Geomagnetically Quiet Sunlit Polar Cap Region

We consider the formation of a potential drop over the Earth's polar cap during geomagnetically quiet daytime. The observed potential drop is primarily defined by the hydrogen, photoelectron, and polar rain fluxes ratios and depends strongly on the energy distribution of the photoelectron flux. Polar rain is an essential component of the model required for plasma quasineutrality. The potential distribution along the magnetic field line has two regions, with a small, gradual, potential drop of 3 to 4 volts and a potential jump. The value of the potential jump depends on the hydrogen ion to photoelectron flux ratio and is also controlled by polar rain electrons. With quasineutrality required at its upper boundary, the jump only occurs in the presence of polar rain and its location depends on the polar rain flux. Model predictions compare well with FAST (Fast Auroral SnapshoT) observations presented by Kitamura et al.(2012, https://doi.org/10.1029/2011JA017459).

Khazanov, G. V.↗
NASA NTRS2019

Formation of the Potential Jump Over the Geomagnetically Quiet Sunlit Polar Cap Region

We consider the formation of a potential drop over the Earth's polar cap duringgeomagnetically quiet daytime. The observed potential drop is primarily defined by the hydrogen,photoelectron, and polar rain fluxes ratios and depends strongly on the energy distribution of thephotoelectron flux. Polar rain is an essential component of the model required for plasma quasineutrality.The potential distribution along the magnetic field line has two regions, with a small, gradual, potentialdrop of 3–4 V and a potential jump. The value of the potential jump depends on the hydrogen ion tophotoelectron flux ratio and is also controlled by polar rain electrons. With quasineutrality required at itsupper boundary, the jump only occurs in the presence of polar rain and its location depends on the polarrain flux. Model predictions compare well with FAST observations presented by Kitamura et al.(2012, https://doi.org/10.1029/2011JA017459).

Khazanov, George V.↗
NASA NTRS2020

Water Ice Cloud Feedbacks over the North Polar Residual Cap at Moderate Obliquity

Several global climate modeling studies have now shown that water ice clouds can warm the surface 10s of K at moderate obliquities [1,2,3]. Significant greenhouse warming occurs because the predicted clouds are optically thick, the cloud particles are large enough to efficiently interact with infrared radiation, and the clouds either form at or are transported to high altitudes where the atmosphere is cold. Radiativedynamic feedbacks play a critical role in producing the conditions needed for a strong cloud greenhouse. Two feedbacks have been identified: one involves atmospheric warming by clouds aloft at lower latitudes. These clouds are generally associated with the global Hadley circulation. The second feedback involves clouds that form over the North Polar Residual Cap (NPRC) during summer. These clouds are more closely associated with the regional polar circulation. We focus here on the second of these feedbacks with the goal of understanding the details of the interactions between sublimation, cloud formation and transport in the north polar region. We show that these feedbacks strongly control the wetness of the atmosphere and the strength of the cloud greenhouse at moderate obliquity.

Kahre, M. A.↗
NASA NTRS2024

Assessing Coulomb Collision Contributions to Photoelectron Deceleration above Earth’s Polar Caps

NASA’s Endurance rocket mission resolved a subtle energy shift in photoelectrons escaping from Earth’s polar caps, from which the first successful measurement of Earth’s ambipolar electrostatic field was made. Preflight models predicted that coulomb collisions with thermal electrons could add an extra energy shift of up to 1 eV. However, no such additional shift was reported in the initial analysis. Here, we identify a previously unreported effect related to the spacecraft wake, which introduced a systematic +0.25eV energy shift that countered and masked the shift from coulomb collisions. After applying an in-flight calibration for this wake effect, we find a total photopeak energy shift consistent with the combined influence of the ambipolar field and the subtler -0.37eV coulomb shift, predicted by the fully kinetic STET model. Further analysis of these recalibrated measurements yields an ambipolar field estimate in close agreement with the initial analysis.

Glyn A Collinson↗