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At least 361 records · Page 20

Space plasma physics results from Spacelab 1

The Spacelab 1 payload carried several instrument systems which together investigated a number of space plasma phenomena. These experiments used the Space Shuttle Orbiter as a platform for making controlled particle-beam, plasma and neutral gas inputs to the ionosphere and magnetosphere and for observing the outputs produced. Spacelab 1 space-plasma investigations included the Space Experiments with Particle Accelerators (SEPAC), Phenomena Induced by Charged Particle Beams (PICPAB), Atmospheric Emissions Photometric Imaging (AEPI) and the Low Energy Electron Spectrometer and Magnetometer. Among the major phenomena investigated both singly and jointly by these experiments are vehicle charging and neutralization, beam-plasma and wave-particle interactions, anomalous ionization phenomena produced by neutral-gas and plasma injections and several phenomena induced by modulated particle beam injections.

Burch, J. L.↗

Various Ambiguities in Re-constructing Laser Pulse Parameters

We think that mode lock laser pulses are generated by the summation process that take place between the monochromatic EM filed frequencies as if they interact with each other as shown in equation 1. In reality, the pulse generation is a collaborative interaction process between EM fields and various material medium. When we carry out the actual mode lock analysis, we do take into account of interpaly between all the temporal dynamics of the cavity gain medium, cavity round trip time and the response time of the intra cavity element (saturable absorber, Kerr medium, etc.). that really enforces the locking of the phase of the cavity spontaneous emissions. On a conceptual level, this simplistic representation of the mode locking by Eq.1 ignores all these critical physical processes. When we try to analyze a pulsed field, again we start by representing it very much like this equation, even though we can only detect the square modulus of this complex field and loose a lot of phase related information to the detectors quantum whims and their time constants. The key parameters for a light pulse are as follows. Foremost is the (i) carrier frequency, which cannot be described or imagined without its state of undulation expressed as its (ii) phase. Next is our imagined time finite (iii) carrier envelope that provides the temporal boundary of the field amplitude strength of the undulating E-field. The final parameter is the (iv) state of polarization or the unique plane along which the strength of the E-field gradient undulates. None of these filed characteristics are made self-evident to us by the fields themselves. We do not see light. Light does not see light. Light beams pass through each other without altering each others energy distribution unless there are interacting material molecules (dipoles) within the physical volume of superposition of the beams. In contrast, we can sense the material particles. Material particles sense each other and they cannot pass through each other without interacting with (scattering from) each other. Thus the interpretation of the superposition phenomenon of multiple fields on detectors should not be lumped under the mysterious "wave-particle duality" philosophy. The phenomenon of superposition can be understood better when we focus on the actual process experienced by the detecting dipoles when allowed by QM rules, they respond to and sum all the induced stimulations due to all the superposed fields followed by the proportionate energy absorption giving rise to the fringes we observe. We will present various experimental results to illustrate our arguments. Our position is that such detector behavior driven interpretations rather than the generally implied field-field interaction driven explanations, will help us better understand the ultimate nature of light and hence invent better and newer devices and instruments.

Roychoudhuri, Chandrasekhar↗

Quantifying Energy Conversion in Higher-Order Phase Space Density Moments in Plasmas

Weakly collisional and collisionless plasmas are typically far from local thermodynamic equilibrium (LTE), and understanding energy conversion in such systems is a forefront research problem. The standard approach is to investigate changes in internal (thermal) energy and density, but this omits energy conversion that changes any higher-order moments of the phase space density. In this Letter, we calculate from first principles the energy conversion associated with all higher moments of the phase space density for systems not in LTE. Particle-in-cell simulations of collisionless magnetic reconnection reveal that energy conversion associated with higher-order moments can be locally significant. Furthermore, the results may be useful in numerous plasma settings, such as reconnection, turbulence, shocks, and wave-particle interactions in heliospheric, planetary, and astrophysical plasmas.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

Current-driven plasma acceleration versus current-driven energy dissipation. III - Anomalous transport

In the present paper the linear stability description and weak turbulence theory are used to develop a second order description of wave-particle transport and anomalous dissipation. The goal is to arrive at anomalous transport coefficients that can be readily included in fluid flow codes. In particular, expressions are derived for the heating rates of ions and electrons by the unstable waves and for the electron-wave momentum exchange rate that controls the anomalous resistivity effect. Comparative calculations were undertaken assuming four different saturation models: ion trapping, electron trapping, ion resonance broadening, and thermodynamic bound. A foremost finding is the importance of the role of electron Hall parameter in scaling the level of anomalous dissipation for the parameter range of the MPD thruster plasma. Polynomial expressions of the relevant transport coefficients cast solely in terms of macroscopic parameters are also obtained for inclusion in plasma fluid codes for the self-consistent numerical simulation of real thruster flows including microturbulent effects.

Choueiri, Edgar Y.↗

Outer Radiation Belt Dropout Dynamics Following the Arrival of Two Interplanetary Coronal Mass Ejections

Magnetopause shadowing and wave-particle interactions are recognized as the two primary mechanisms for losses of electrons from the outer radiation belt. We investigate these mechanisms, sing satellite observations both in interplanetary space and within the magnetosphere and particle drift modeling. Two interplanetary shocks sheaths impinged upon the magnetopause causing a relativistic electron flux dropout. The magnetic cloud (C) and interplanetary structure sunward of the MC had primarily northward magnetic field, perhaps leading to a concomitant lack of substorm activity and a 10 day long quiescent period. The arrival of two shocks caused an unusual electron flux dropout. Test-particle simulations have shown 2 to 5 MeV energy, equatorially mirroring electrons with initial values of L 5.5can be lost to the magnetosheath via magnetopause shadowing alone. For electron losses at lower L-shells, coherent chorus wave-driven pitch angle scattering and ULF wave-driven radial transport have been shownto be viable mechanisms.

Alves, L. R.↗

Transverse ion acceleration by localized lower hybrid waves in the topside auroral ionosphere

Up to now, observations had been unable to show conclusively a one-to-one correspondence between perpendicular ion acceleration and a particular type of plasma wave within the O(+) source region below 2000 km. In this paper we demonstrate that intense (100-300 mV/m) lower hybrid waves are responsible for transversely accelerating H(+) and O(+) ions to characteristic energies of up to 6 eV. This wave-particle interaction takes place in thin filamentary density cavities oriented along geomagnetic field lines. The measurements we discuss were conducted in the nightside auroral zone at latitudes between 500 km and 1100 km. Our results are consistent with theories of lower hybrid wave condensation and collapse.

Vago, J. L.↗

Approximate two-body generating Hamiltonian for the particle-hole Pfaffian wave function

We present two two-body Hamiltonians that approximate the exact particle-hole Pfaffian wave function with their ground states for all the system sizes where this wave function has been numerically constructed to date. The approximate wave functions have high overlap with the original and reproduce well the low-lying entanglement spectrum and structure factor. The approximate generating Hamiltonians are obtained by an optimization procedure where three to four pseudopotentials are varied in the neighbourhood of second Landau level Coulomb interaction or of a noninteracting model. They belong to a finite region in the variational space of Hamiltonians where each point approximately generates the particle-hole Pfaffian. Here we diagonalize the identified Hamiltonians for up to 20 electrons and find that for them the particle-hole Pfaffian shift appears energetically more favorable. The possibility to interpret the data in terms of composite fermions is discussed.

36 MATERIALS SCIENCE↗

Satellite and ground-based observations of a red arc.

Simultaneous observations carried out during the red-arc period of Aug. 8-9, 1970 at Richland, Washington and by the Ogo 6 satellite are examined in the light of the present-day theoretical knowledge. The observed formation of the arc at the electron temperature peak and density trough supports the thermal-conduction theory of red-arc formation. The lack of dc electric fields in the red-arc region rules out these fields as an excitation mechanism. Particle precipitation as a direct source of red-line emission can also be ruled out by the observations presented. The formation of the arc in the plasmapause region and the detection of low-frequency ac fields are consistent with a theory that predicts wave-particle interaction at the plasmapause as a mechanism for supplying thermal energy to the plasmasphere electrons.

Nagy, A. F.↗

Pitch-angle diffusion by whistler mode waves near the Io plasma torus

As Voyager 1 traversed the inner radiation belt of Jupiter, wave-particle interactions involving energetic electrons and whistler mode turbulence were strongly affected by the presence of the Io plasma torus. Within the high density torus the resonant electron energy was low and the associated high index of refraction yielded high B-to-E ratios for the wave fields, leading to very strong pitch-angle scattering. It is shown that significant spatial and temporal variations in plasma conditions produced large fluctuations in local scattering times, and the problems associated with the evaluation of precipitation lifetime are discussed.

Scarf, F. L.↗

Simultaneous Observation of Two Isolated Proton Auroras at Subauroral Latitudes by a Highly Sensitive All-Sky Camera and Van Allen Probes

Isolated proton auroras (IPAs) appearing at subauroral latitudes are generated by energetic protons precipitating from the magnetosphere through interaction with electromagnetic ion cyclotron (EMIC) waves. An IPA thus indicates the spatial scale and temporal variation of wave-particle interactions in the magnetosphere. In this study, a unique event of simultaneous ground and magnetospheric satellite observations of two IPAs were conducted on March 16, 2015, using an all-sky imager at Athabasca, Canada and Van Allen Probes. The Van Allen Probes observed two isolated EMIC waves with frequencies of ~1 and 0.4 Hz at L ≈ 5.0 when the satellite footprint crossed over the two IPAs. This suggests that the IPAs were caused by localized EMIC waves. Proton flux at 5–20 keV increased locally when the EMIC waves appeared. Electron flux at energies below ~500 eV also increased. Temperature anisotropy of the energetic protons was estimated at 1.5–2.5 over a wide L-value range of 3.0–5.2. Electron density gradually decreased from L = 3.5 to 5.4, suggesting that the EMIC wave at L ≈ 5.0 was located in the gradual plasmapause. From these observations, we conclude that the localized IPAs and associated EMIC waves took place because of localized enhancement of energetic proton flux and plasma density structure near the plasmapause. Furthermore, the magnetic field observed by the satellite showed small variation during the wave observation, indicating that the IPAs were accompanied by the weak field-aligned current.

59 BASIC BIOLOGICAL SCIENCES↗

Kinetic plasma processes occurring in the outer plasmasphere

One area of data analysis work that was begun under this contract is the fitting of the perpendicular velocity distributions of equatorially trapped ions with a Kappa function. This type of characterization of the trapped ions will be very useful for comparison with velocity distributions produced by the model. A second area of data analysis is to study data from consecutive passes when DE 1's apogee was near the magnetic equator and the spacecraft was often skimming along nearly the same L shell. In 1982 three such periods occurred in May, June, and July. For these consecutive events we have Kp histories, density measurements from a number of sources (Whistler data, DE SFR, ISEE SFR) and consecutive samples of ion pitch angle distributions along field lines. It is clear from this data how the pitch angle distributions evolve during a flux tube refilling event. Our modeling of the flow of plasma along closed field lines is following two basic tracks. The first is a study of the basic refilling process without the effect of wave-particle heating near the equator or the effect of large or abrupt field-aligned electric potential drops. This model includes the effects of Coulomb self-collisions and collisions with the O+ ions in the topside ionosphere. The second track is a study of the effects of wave produced pitch-angle scattering and perpendicular heating occurring near the magnetic equator, in connection with the development of large potential drops that result from electron heating and the development of density gradients.

Wilson, Gordon R.↗

Direct observations in the dusk hours of the characteristics of the storm-time ring current particles during the beginning of magnetic storms

The characteristic features of the initial enhancement of the storm-time ring current particles in the evening hours are consistent with flow patterns resulting from a combination of inward convection, gradient drift, and corotation which carries plasma sheet protons into low L-values near midnight and the higher energy proton component into the plasmasphere and through the evening hours. Data from four magnetic storms during the early life of Explorer 45, when the local time of apogee was in the afternoon and evening hours, show that protons with lower magnetic moments penetrate deeper into the magnetosphere until a low limit, determined by the corotation and gradient drift forces, is reached. Such particle motions produce the stable energy dependent inner boundary of the ring current protons inside the plasmapause in the dusk sector and also provide the mechanism for energy injection into the ring current region. From the analyses of the pitch angle distributions it is evident that charge exchange and wave particle interactions are not the dominant causes of this inner boundary.

Smith, P. H.↗

Generation of plasma waves by thick-target electron beams, and the expected radiation signature

The production of plasma waves by a nonthermal beam of high-energy electrons injected into a background thermal plasma was investigated. The coupled kinetic equations for nonthermal electrons were solved, and the level of the plasma waves produced by the bump-on-tail instability arising as a result of the Coulomb collisions of nonthermal electrons with background plasma was estimated. In addition, the radiation signatures of these waves were examined. It is shown that the wave-particle interactions have a significant effect on the overall distribution of the electrons and that it is unlikely that such effects can be discerned in the observed bremsstrahlung or synchrotron radiation of the nonthermal electrons. However, a significant fraction of the energy lost by the beam is transferred to plasma waves and is then dissipated by the thermal plasma.

Hamilton, Russell J.↗

Superthermal Electron Magnetosphere-Ionosphere Coupling in the Diffuse Aurora in the Presence of ECH Waves

There are two main theories for the origin of the diffuse auroral electron precipitation: first, pitch angle scattering by electrostatic electron cyclotron harmonic (ECH) waves, and second, by whistler mode waves. Precipitating electrons initially injected from the plasma sheet to the loss cone via wave-particle interaction processes degrade in the atmosphere toward lower energies and produce secondary electrons via impact ionization of the neutral atmosphere. These secondary electrons can escape back to the magnetosphere, become trapped on closed magnetic field lines, and deposit their energy back to the inner magnetosphere. ECH and whistler mode waves can also move electrons in the opposite direction, from the loss cone into the trap zone, if the source of such electrons exists in conjugate ionospheres located at the same field lines as the trapped magnetospheric electron population. Such a situation exists in the simulation scenario of superthermal electron energy interplay in the region of diffuse aurora presented and discussed by Khazanov et al. (2014) and will be quantified in this paper by taking into account the interaction of secondary electrons with ECH waves.

Coupling↗

Lower hybrid heating of ionospheric ions due to ion ring distributions in cusp

The stability of H(+) and H(++) ring distributions which have been observed downflowing into the cusp on the DE and S3-3 satellites is examined in the context of the feedback of those instabilities on plasma of ionospheric origin consisting of (H(+) and O(+). Lower hybrid waves are excited by the ring distributions in three distinct phases of wave-particle interaction: linear growth, trapping, and quasi-linear diffusion.The latter phase accounts for most particle heating. Including background O(+) and/or a He(++) ring introduces new modes not present in a pure H(+) plasma which play an important role in heating heavier ions. O(+) is heated significantly more by a He(++) ring than a H(+) ring of comparable energy density. It is suggested that lower hybrid waves generated by downflowing ion ring distributions play a role in energizing ion conics in the cusp.

Roth, I.↗

Sources and acceleration of energetic particles in planetary magnetospheres

Energetic particles in the magnetospheres of the solar system originate from various different sources, such as the solar wind, the planetary ionospheres as well as the moons and rings of the planetary systems. Important acceleration sites are the auroral regions, the magnetotail, and the equatorial regions of the magnetospheres where electric fields, wave-particle interactions, and magnetic pumping are among the major acceleration mechanisms proposed. Over the last decade mass- and charge-sensitive particle spectrometers on satellites and space probes have collected a wealth of information about the relative contribution of the various particle sources and the major acceleration processes to the energetic particle populations. Emphasis will be put on recent studies of the source populations and the acceleration processes in the Earth's auroral zones and magnetotail. Furthermore, the Jovian system with the largest magnetosphere and its unique mixture of particle sources with strong contributions from moons will be highlighted in some results from Ulysses.

Moebius, Eberhard↗

Quantum-metric-induced quantum Hall conductance inversion and reentrant transition in fractional Chern insulators

The quantum metric of single-particle wave functions in topological flat bands plays a crucial role in determining the stability of fractional Chern insulating (FCI) states. Here, we unravel that the quantum metric causes the many-body Chern number of the FCI states to deviate sharply from the expected value associated with partial filling of the single-particle topological flat band. Furthermore, the variation of the quantum metric in momentum space induces band dispersion through interactions, affecting the stability of the FCI states. This causes a reentrant transition into the Fermi liquid from the FCI phase as the interaction strength increases. Published by the American Physical Society 2024

Wu, Ang-Kun (ORCID:0000000270181674)↗

Wave propagation in the magnetosphere of Jupiter

A systematic procedure is developed for identifying the spatial regimes of various modes of wave propagation in the Jupiter magnetosphere that may be encountered by flyby missions. The Clemmow-Mullaly-Allis (CMA) diagram of plasma physics is utilized to identify the frequency regimes in which different modes of propagation occur in the magnetoplasma. The Gledhill model and the Ioannidis and Brice model of the magnetoplasma are summarized, and configuration-space CMA diagrams are constructed for each model for frequencies from 10 Hz to 1 MHz. The distinctive propagation features, the radio noise regimes, and the wave-particle interactions are discussed. It is concluded that the concentration of plasma in the equatorial plane makes this region of vital importance for radio observations with flyby missions. Local radio noise around the electron cyclotron frequency will probably differ appreciably from its terrestrial counterpart due to the lack of field-line guidance. Hydromagnetic wave properties at frequencies near the ion cyclotron frequency and below will probably be similar to the terrestrial case.

Liemohn, H. B.↗