Optimization of radial diffusion coefficients for the proton radiation belt during the CRRES era

Proton flux measurements from the Proton Telescope instrument aboard the CRRES satellite are revisited, and used to drive a radial diffusion model of the inner proton belt at 1.1 ≤ L ≤ 1.65. Our model utilises a physics‐based evaluation of the cosmic ray albedo neutron decay (CRAND) source, and coulomb collisional loss is driven by a drift averaged density model combining results from the International Reference Ionosphere, NRLMSIS‐00 atmosphere and Radio Plasma Imager plasmasphere models, parameterised by solar activity and season. We drive our model using time‐averaged data at L = 1.65 to calculate steady state profiles of equatorial phase space density, and optimise our choice of radial diffusion coefficients based on four defining parameters to minimise the difference between model and data. This is first performed for a quiet period when the belt can be assumed to represent steady state. Additionally, we investigate fitting steady state solutions to time averages taken during active periods where the data exhibits limited deviation from steady state, demonstrated by CRRES measurements following the 24th March 1991 storm. We also discuss a way to make the optimisation process more reliable by excluding periods of variability in plasmaspheric density from any time average. Lastly, we compare our resultant diffusion coefficients to those derived via a similar process in previous work, and diffusion coefficients derived for electrons from ground and in situ observations. We find that higher diffusion coefficients are derived compared with previous work, and suggest more work is required to derive proton diffusion coefficients for different geomagnetic activity levels

D 3. 3 Final performance results and consolidated view on the most promising multi -node/multi -antenna transmission technologies

This document provides the most recent updates on the technical contributions and research challenges focused in WP3. Each Technology Component (TeC) has been evaluated under possible uniform assessment framework of WP3 which is based on the simulation guidelines of WP6. The performance assessment is supported by the simulation results which are in their mature and stable state. An update on the Most Promising Technology Approaches (MPTAs) and their associated TeCs is the main focus of this document. Based on the input of all the TeCs in WP3, a consolidated view of WP3 on the role of multinode/multi-antenna transmission technologies in 5G systems has also been provided. This consolidated view is further supported in this document by the presentation of the impact of MPTAs on METIS scenarios and the addressed METIS goals.Aziz, D.; Baracca, P.; De Carvalho, E.; Fantini, R.; Rajatheva, N.; Popovski, P.; Sørensen, JH.... (2015). D 3. 3 Final performance results and consolidated view on the most promising multi -node/multi -antenna transmission technologies. http://hdl.handle.net/10251/7675

D3.2 First performance results for multi -node/multi -antenna transmission technologies

This deliverable describes the current results of the multi-node/multi-antenna technologies investigated within METIS and analyses the interactions within and outside Work Package 3. Furthermore, it identifies the most promising technologies based on the current state of obtained results. This document provides a brief overview of the results in its first part. The second part, namely the Appendix, further details the results, describes the simulation alignment efforts conducted in the Work Package and the interaction of the Test Cases. The results described here show that the investigations conducted in Work Package 3 are maturing resulting in valuable innovative solutions for future 5G systems.Fantini. R.; Santos, A.; De Carvalho, E.; Rajatheva, N.; Popovski, P.; Baracca, P.; Aziz, D.... (2014). D3.2 First performance results for multi -node/multi -antenna transmission technologies. http://hdl.handle.net/10251/7675

Modélisation du phénomène de diffusion radiale au sein des ceintures de radiation terrestres par technique de changement d’échelle

This study falls within the field of the Earth’s radiation belt dynamics. It consists of modeling the radial diffusion process based on a spatiotemporal resolution higher than the resolution at which radiation belt dynamics are described in terms of a diffusion equation. The approach has been organized in three parts. First, we described radial diffusion theoretically, highlighting the main drivers of the phenomenon and giving a ready-made formula of the radial diffusion coefficients. Then, based on this formula, we aimed to quantify the radial diffusion coefficients. In order to reach this goal, we developed analytical and numerical procedures, and then, observational procedures. Finally, we discussed the results and the pros and cons of each method. This study highlights the central role of asymmetric variations of the electromagnetic fields and induced electric fields in the driving of the intensity of the radial diffusion process. It provides tracks for numerical and experimental quantification of these two drivers. It also provides tools for a critical review of the literature. It paves the way for a more accurate determination of radial diffusion coefficients based on a more precise description of the electromagnetic environment and its variations.Cette étude s’inscrit dans le domaine de la description de la dynamique des ceintures de radiation terrestres. Elle consiste à modéliser le phénomène de diffusion radiale en travaillant avec une résolution spatio-temporelle plus fine que celle utilisée pour décrire la dynamique des ceintures par le biais d’une équation de diffusion. La démarche s’est organisée en trois temps. Tout d’abord, l’objectif a été d’étudier le phénomène de diffusion radiale d’un point de vue théorique afin de mettre en lumière les principaux pilotes du processus et d’expliciter une formulation des coefficients de diffusion radiale. Une fois l’expression de ces coefficients établie, l’objectif a ensuite été de les quantifier. Pour cela, nous avons développé des protocoles analytiques et numériques puis des protocoles expérimentaux. Nous avons discuté les résultats obtenus ainsi que les atouts et les limites de ces protocoles. Cette étude met en évidence le rôle central de l’asymétrie des variations du champ électromagnétique et des champs électriques induits dans le processus de diffusion radiale. Elle propose des pistes pour la quantification numérique et expérimentale de ces deux pilotes. Elle apporte également un regard critique sur les travaux de la littérature. Elle ouvre la voie pour une nouvelle quantification des coefficients de diffusion basée sur une modélisation adéquate de la dynamique de l’environnement électromagnétique

Direct Observation of Radiation-Belt Electron Acceleration from Electron-Volt Energies to Megavolts by Nonlinear Whistlers

International audienceThe mechanisms for accelerating electrons from thermal to relativistic energies in the terrestrial magnetosphere, on the sun, and in many astrophysical environments have never been verified. We present the first direct observation of two processes that, in a chain, cause this acceleration in Earth's outer radiation belt. The two processes are parallel acceleration from electron-volt to kilovolt energies by parallel electric fields in time-domain structures (TDS), after which the parallel electron velocity becomes sufficiently large for Doppler-shifted upper band whistler frequencies to be in resonance with the electron gyration frequency, even though the electron energies are kilovolts and not hundreds of kilovolts. The electrons are then accelerated by the whistler perpendicular electric field to relativistic energies in several resonant interactions. TDS are packets of electric field spikes, each spike having duration of a few hundred microseconds and containing a local parallel electric field. The TDS of interest resulted from nonlinearity of the parallel electric field component in oblique whistlers and consisted of ∼0.1 msec pulses superposed on the whistler waveform with each such spike containing a net parallel potential the order of 50 V. Local magnetic field compression from remote activity provided the free energy to drive the two processes. The expected temporal correlations between the compressed magnetic field, the nonlinear whistlers with their parallel electric field spikes, the electron flux and the electron pitch angle distributions were all observed. Rapid acceleration of electrons up to relativistic energies occurs in different plasma configuration on all scales from the laboratory to astrophysics. The Van Allen radiation belts around Earth contain such relativistic electrons that are trapped in Earth's magnetic field. Because of intrinsic interest in the acceleration mechanism, because these electrons may be prototypical of relativistic electron acceleration in other environments, and because they present a danger to space travelers and spacecraft, it is important to understand their origin and acceleration. Two possible sources of these electrons that have been discussed are injections into the local environment of electrons that were energized by moving earthward from the tail into a stronger magnetic field while conserving their first two adiabatic invariants [1], and local acceleration in the region of the satellite measurements. While both mechanisms occur, the local acceleration mechanism has been shown to be more important, at least for major, rapid, relativistic flux increases [2–4]. Simulations of rela-tivistic electron acceleration via the whistler mode resonance have produced relativistic electrons from seed populations of hundreds of keV electrons [5,6]. This work has left open the question of the source of such seed populations. Meanwhile, observations have been made in Earth's radiation belts of parallel (to the local magnetic field) electric fields in the form of packets of spikes, each spike having a duration the order of 100 msec, and each packet containing hundreds of such spikes [7]. These spikes, dubbed time-domain structures, have at least five different forms that satisfy the above description and they have been suggested as the mechanism for producing the ∼100 keV electrons that are the seed population for whistler wave acceleration to highly relativistic energies [7]. This suggestion has not been verified by detailed comparison of particles and fields before the studies described in this Letter that show, for the first time, both that low energy electrons can be accelerated up to keV energies by the parallel electric fields in time-domain structures and that such keV electrons can be further accelerated to relativistic energies via the whistler mode resonance even though their initial energies are significantly less than ∼100 keV. The data in this Letter were collected on May 2, 2013 on Van Allen probe B (VAP-B) by the electric field experiment [8], the magnetic field experiment [9], and the Energetic particle, Composition, and Thermal plasma (RBSP-ECT) Suite experiments [10–12]. The spacecraft was at a magnetic latitude of 2°, a magnetic local time of midnight, and a geocentric radial distance of 5.8 Earth radii during these measurements. Figure 1 illustrates three components of the electric and magnetic fields in the background-magnetic-field-aligned coordinate system during a 20 msec interval in which two packets of nonlinear whistlers were observed. Panels 1(a) and 1(b) give the two perpendicular (to the background magneti

Saturn's Inner Magnetospheric Convection in the View of Zebra Stripe Patterns in Energetic Electron Spectra

Banded structures observed in energetic particle spectrograms in the Earth's inner radiation belt and slot region, that is, “zebra stripes,” have been resolved in the Saturnian magnetosphere with Cassini. This study implements a large-scale statistical analysis of Saturnian zebra stripe properties in association with the noon-to-midnight electric field of the inner magnetosphere to which the stripes' origin was recently established. Cassini has detected zebra stripes extending between L-shells (L) of 5–9 for more than half of the orbits that crossed inward of L = 9. The amplitude of the stripes is 15 - 20% on average above the background differential energy flux, and their age is estimated to be 20–60 hr. The regular observation of zebra stripes suggests that their regeneration and the corresponding electric field enhancements develop over timescales comparable to their estimated lifetime (days), revealing that internal processes contribute to the electric field dynamics, in addition to a solar wind-induced variability indicated by previous investigations. The flux-enhanced stripes are traced back to the dayside, preferentially from postnoon, indicating an electric field orientation from postnoon to postmidnight. Our results further suggest that the electric field's offset from the noon-midnight line is subject to both L-shell and temporal dependencies, confirming the previous inferred variability

Time domain structures: What and where they are,what they do, and how they are made

International audienceTime domain structures (TDS) (electrostatic or electromagnetic electron holes, solitary waves,double layers, etc.) are ≥1ms pulses having significant parallel (to the background magnetic field) electricfields. They are abundant through space and occur in packets of hundreds in the outer Van Allen radiationbelts where they produce magnetic-field-aligned electron pitch angle distributions at energies up to ahundred keV. TDS can provide the seed electrons that are later accelerated to relativistic energies by whistlersand they also produce field-aligned electrons that may be responsible for some types of auroras. Thesefield-aligned electron distributions result from at least three processes. The first process is parallel accelerationby Landau trapping in the TDS parallel electric field. The second process is Fermi acceleration due toreflection of electrons by the TDS. The third process is an effective and rapid pitch angle scattering resultingfrom electron interactions with the perpendicular and parallel electric and magnetic fields of many TDS.TDS are created by current-driven and beam-related instabilities and by whistler-related processes such asparametric decay of whistlers and nonlinear evolution from oblique whistlers. New results on the temporalrelationship of TDS and particle injections, types of field-aligned electron pitch angle distributions producedby TDS, the mechanisms for generation of field-aligned distributions by TDS, the maximum energies offield-aligned electrons created by TDS in the absence of whistler mode waves, TDS generation by obliquewhistlers and three-wave-parametric decay, and the correlation between TDS and auroral particle precipitation,are presented