The Time-of-Flight Energy,Angle, Mass Spectrograph (Teams) Experiment for Fast

The Time-of-flight Energy Angle Mass Spectrograph (TEAMS) is being flown on the FAST Small Explorer mission to measure the 3-dimensional distribution function of the major ion species present in the lower magnetosphere. The instrument is similar to time-of-flight plasma analyzer systems that have been designed and planned for flight as CODIF (COmposition and DIstribution Function analyzer) on the four European Space Agency Cluster-II spacecraft and, as ESIC (Equator-S Ion Composition instrument) on Equator-S. This instrument allows the 3-dimensional distribution functions of individual ion species to be determined within spin period (2.5 s). Two-dimensional distributions are measured in 80 ms. These capabilities are crucial for the study of selective energization processes in the auroral regions of the magnetosphere. The design, operational characteristics, and test and calibration results for this instrument are presented. The sensor consists of a toroidal top-hat electrostatic analyzer with instantaneous acceptance of ions over 360° in polar angle. After post-acceleration of the incoming ions by up to 25 kV, a time-of-flight mass spectrograph discriminates the individual species. It has been demonstrated through calibration that the instrument can easily separate H⁺, He²⁺, He⁺, O⁺ and, for energies after post-acceleration of > 20 keV, even O₂ ⁺ molecules. On-board mass discrimination and the internal accumulation of several distinct data quantities combined with the spacecraft's flexible telemetry formatting allow for instrument data rates from 7.8 kb s^–1 to 315 kb s^–1 to be telemetered to ground through the FAST centralized Instrument Data Processor.     

The Extreme Ultraviolet Imager Investigation for the IMAGE Mission

The Extreme Ultraviolet Imager (EUV) of the IMAGE Mission will study the distribution of He⁺ in Earth's plasmasphere by detecting its resonantly-scattered emission at 30.4 nm. It will record the structure and dynamics of the cold plasma in Earth's plasmasphere on a global scale. The 30.4-nm feature is relatively easy to measure because it is the brightest ion emission from the plasmasphere, it is spectrally isolated, and the background at that wavelength is negligible. Measurements are easy to interpret because the plasmaspheric He⁺ emission is optically thin, so its brightness is directly proportional to the He⁺ column abundance. Effective imaging of the plasmaspheric He⁺ requires global `snapshots in which the high apogee and the wide field of view of EUV provide in a single exposure a map of the entire plasmasphere. EUV consists of three identical sensor heads, each having a field of view 30° in diameter. These sensors are tilted relative to one another to cover a fan-shaped field of 84°×30°, which is swept across the plasmasphere by the spin of the satellite. EUVs spatial resolution is 0.6° or 0.1 R _E in the equatorial plane seen from apogee. The sensitivity is 1.9 count s^–1 Rayleigh^–1, sufficient to map the position of the plasmapause with a time resolution of 10 min.     

Heavy ions in the magnetosphere

For purposes of this review heavy ions include all species of ions having a mass per unit charge of 2 AMU or greater. The discussion is limited primarily to ions in the energy range between 100 eV and 100 keV. Prior to the discovery in 1972 of large fluxes of energetic O⁺ ions precipitating into the auroral zone during geomagnetic storms, the only reported magnetosphere ion species observed in this energy range were helium and hydrogen. More recently O⁺ and He⁺ have been identified as significant components of the storm time ring current, suggesting that an ionosphere source may be involved in the generation of the fluxes responsible for this current. Mass spectrometer measurements on board the S3-3 satellite have shown that ionospheric ions in the auroral zone are frequently accelerated upward along geomagnetic field lines to several keV energy in the altitude region from 5000 km to greater than 8000 km. These observations also show evidence for acceleration perpendicular to the magnetic field and thus cannot be explained by a parallel electric field alone. This auroral acceleration region is most likely the source for the magnetospheric heavy ions of ionospheric origin, but further acceleration would probably be required to bring them to characteristic ring current energies. Recent observations from the GEOS-1 spacecraft combined with earlier results suggest comparable contributions to the hot magnetopheric plasma from the solar wind and the ionosphere.Proceedings of the Symposium on Solar Terrestrial Physics held in Innsbruck, May–June 1978.     

Observations of substorm-associated particle-flux variations at 6⩽L⩽8 with GEOS-1

Measurements made with the charged particle spectrometer of the Max-Planck-Institut für Aeronomie onboard GEOS-1 were used to investigate the behaviour of energetic electrons and ions in the dusk sector of the magnetosphere. During substorms the integral ion flux ( 24 KeV) increased whereas the integral electron flux ( 20 KeV) first decreased and later on also increased. The dependences of these flux variations on pitch-angle and particle energy are described and discussed in terms of particle drift in the geomagnetic and geoelectric fields and adiabatic energy variations. The results also provide some information on the source region of the drifting particles.     

Electron density and temperature,as measured by the mutual impedance experiment on board GEOS-1

The mutual impedance experiment on GEOS-1 provides an original diagnostic of the thermal electron population. The electron density N _e, and temperature T _e, are derived from the plasma frequency and Debye length, the values of which determine the shape of the frequency dependent mutual impedance curves. The existing limits of the method are pointed out. They may be instrumental or arise from a lack of theoretical development, for instance when the steady magnetic field or the drift velocity of the plasma cannot be neglected. Nevertheless, first geophysical results have been derived, using measurements obtained on the dayside of the equatorial magnetosphere where most of the data enter within the above limits. In particular, we have drawn a map of the dayside magnetosphere, in terms of densities, Debye lengths, temperatures, at geocentric distances of 4 to 7 Earth radii. The conventional shape of the plasmasphere is recognized, but the temperatures obtained are lower than expected (2 eV at apogee, outside the plasmasphere). The influence of the magnetic activity on apogee measurements is reported: N _e values and A _m indices are shown to be correlated, but it is not the case for T _e and A _m. Finally, detailed T _e and N _e profiles are shown, and the presence of a plasmapause boundary is discussed.     

Voyager energetic particle observations at interplanetary shocks and upstream of planetary bow shocks: 1977–1990

The Voyager 1 and 2 spacecraft include instrumentation that makes comprehensive ion (E 28 keV) and electron (E 22 keV) measurements in several energy channels with good temporal, energy, and compositional resolution. Data collected over the past decade (1977–1988), including observations upstream and downstream of four planetary bow shocks (Earth, Jupiter, Saturn, Uranus) and numerous interplanetary shocks to 30 AU, are reviewed and analyzed in the context of the Fermi and shock drift acceleration (SDA) models. Principal findings upstream of planetary bow shocks include the simultaneous presence of ions and electrons, detection of tracer ions characteristic of the parent magnetosphere (O, S, O⁺), power-law energy spectra extending to 5 MeV, and large (up to 100:1) anisotropies. Results from interplanetary shocks include observation of acceleration to the highest energies ever seen in a shock ( 22 MeV for protons, 220 MeV for oxygen), the saturation in energy gain to 300 keV at quasi-parallel shocks, the observation of shock-accelerated relativistic electrons, and separation of high-energy (upstream) from low-energy (downstream) populations to within 1 particle gyroradius in a near-perpendicular shock. The overall results suggest that ions and electrons observed upstream of planetary bow shocks have their source inside the parent magnetosphere, with first order Fermi acceleration playing a secondary role at best. Further, that quasi-perpendicular interplanetary shocks accelerate ions and electrons most efficiently to high energies through the shock-drift process. These findings suggest that great care must be exercised in the application of concepts developed for heliosphere shocks to cosmic ray acceleration through shocks at supernova remnants.     

The plasma instrumentation for the Galileo Mission

The plasma instrumentation (PLS) for the Galileo Mission comprises a nested set of four spherical-plate electrostatic analyzers and three miniature, magnetic mass spectrometers. The three-dimensional velocity distributions of positive ions and electrons, separately, are determined for the energy-per-unit charge (E/Q) range of 0.9 V to 52 kV. A large fraction of the 4-steradian solid angle for charged particle velocity vectors is sampled by means of the fan-shaped field-of-view of 160°, multiple sensors, and the rotation of the spacecraft spinning section. The fields-of-view of the three mass spectrometers are respectively directed perpendicular and nearly parallel and anti-parallel to the spin axis of the spacecraft. These mass spectrometers are used to identify the composition of the positive ion plasmas, e.g., H⁺, O⁺, Na⁺, and S⁺, in the Jovian magnetosphere. The energy range of these three mass spectrometers is dependent upon the species. The maximum temporal resolutions of the instrument for determining the energy (E/Q) spectra of charged particles and mass (M/Q) composition of positive ion plasmas are 0.5 s. Three-dimensional velocity distributions of electrons and positive ions require a minimum sampling time of 20 s, which is slightly longer than the spacecraft rotation period. The two instrument microprocessors provide the capability of inflight implementation of operational modes by ground-command that are tailored for specific plasma regimes, e.g., magnetosheath, plasma sheet, cold and hot tori, and satellite wakes, and that can be improved upon as acquired knowledge increases during the tour of the Jovian magnetosphere. Because the instrument is specifically designed for measurements in the environs of Jupiter with the advantages of previous surveys with the Voyager spacecraft, first determinations of many plasma phenomena can be expected. These observational objectives include field-aligned currents, three-dimensional ion bulk flows, pickup ions from the Galilean satellites, the spatial distribution of plasmas throughout most of the magnetosphere and including the magnetotail, and ion and electron flows to and from the Jovian ionosphere.     

A three-dimensional plasma and energetic particle investigation for the wind spacecraft

This instrument is designed to make measurements of the full three-dimensional distribution of suprathermal electrons and ions from solar wind plasma to low energy cosmic rays, with high sensitivity, wide dynamic range, good energy and angular resolution, and high time resolution. The primary scientific goals are to explore the suprathermal particle population between the solar wind and low energy cosmic rays, to study particle accleration and transport and wave-particle interactions, and to monitor particle input to and output from the Earth's magnetosphere.Three arrays, each consisting of a pair of double-ended semi-conductor telescopes each with two or three closely sandwiched passivated ion implanted silicon detectors, measure electrons and ions above 20 keV. One side of each telescope is covered with a thin foil which absorbs ions below 400 keV, while on the other side the incoming <400 keV electrons are swept away by a magnet so electrons and ions are cleanly separated. Higher energy electrons (up to 1 MeV) and ions (up to 11 MeV) are identified by the two double-ended telescopes which have a third detector. The telescopes provide energy resolution of E/E0.3 and angular resolution of 22.5°×36°, and full 4 steradian coverage in one spin (3 s).Top-hat symmetrical spherical section electrostatic analyzers with microchannel plate detectors are used to measure ions and electrons from 3 eV to 30 keV. All these analyzers have either 180° or 360° fields of view in a plane, E/E0.2, and angular resolution varying from 5.6° (near the ecliptic) to 22.5°. Full 4 steradian coverage can be obtained in one-half or one spin. A large and a small geometric factor analyzer measure ions over the wide flux range from quiet-time suprathermal levels to intense solar wind fluxes. Similarly two analyzers are used to cover the wide range of electron fluxes. Moments of the electron and ion distributions are computed on board.In addition, a Fast Particle Correlator combines electron data from the high sensitivity electron analyzer with plasma wave data from the WAVE experiment (Bougeretet al., in this volume) to study wave-particle interactions on fast time scales. The large geometric factor electron analyzer has electrostatic deflectors to steer the field of view and follow the magnetic field to enhance the correlation measurements.     

Solar wind charge states measured by ULYSSES/SWICS in the south polar hole

The Ulysses mission now has an extensive data base covering several passes of the south polar coronal hole as the spacecraft proceeds to higher latitudes. Using composition measurements from the SWICS experiment on the Ulysses spacecraft, we have obtained charge state distributions, and hence inferred coronal ionization temperatures, for several solar wind species. In particular, we present an overview of Oxygen ionization temperature measurements, based on the O⁷⁺/O⁶⁺ ratio, for the period January 1993 until April 1994 (23°S to 61°S heliographic latitude), and detailed Oxygen, Silicon and Iron charge state distributions of the south polar hole during a two month period of nearly continuous hole coverage, Dec 1993–Jan 1994 (45°S to 52°S heliographic latitude).     

The plasma mantle: Composition and other characteristics observed by means of the PROGNOZ-7 satellite

A brief summary of the main results of magnetospheric ion composition measurements in general is first presented. PROGNOZ-7 measurements in the nightside plasma mantle are then described and analyzed. Some of the results are the following: In the nightside mantle not too far from midnight the properties of the mantle are sometimes consistent with the open magnetosphere model. However during most magnetic storm situations O⁺ ions appear in the mantle in large proportions and with high energies. The acceleration process affecting the ions has been found in several cases to give equal amounts of energy to all ions independent of mass. Along the flanks of the magnetosphere the flow of the plasma is often low or absent. The O⁺ content is high (up to 20%) and the energy spectrum of both ions and electrons may be very hot, even up to the level of the ring current plasma in the keV range.The O⁺ content in the plasma mantle is positively correlated with the magnetospheric activity level. The mantle, however, does not appear to be the dominating source for the storm time ring current. Direct acceleration of ionospheric ions onto the closed field lines of the plasma sheet and ring current is most likely the main source. The magnetopause on the nightside and along the flanks of the magnetosphere appears to be a fairly solid boundary for mantle ions of ionospheric origin. This is especially evident during periods with high geomagnetic activity, when the mantle is associated with fairly strong fluxes of O⁺ ions.An interesting observation in most of the mantle passages during geomagnetically disturbed periods is the occurrence of intense, magnetosheath like, regions deep inside the mantle. In some cases these regions with strong antisunward flow and with predominant magnetosheath ion composition was observed in the innermost part of the mantle, i.e. marking a boundary region between the lobe and the mantle. These magnetosheath penetration events are usually associated with strong fluxes of accelerated ionospheric ions in nearby parts of the mantle. Evanescent penetration regions with much reduced flow properties are frequently observed in the flank mantle.     

Observations of ion cyclotron waves near synchronous orbit and on the ground

Ion cyclotron waves (hereafter ICW's) generated in the magnetosphere by the ion cyclotron instability of 10–100 keV protons are now known to be the origin of short-period (0.1–5 Hz) electromagnetic field oscillations observed by synchronous spacecraft and on the earth's surface. Observations of the various wave characteristics, including spectral and polarization properties that lead to the identification of generation and propagation mechanisms and regions in the magnetosphere are described with reference to ATS-6, GEOS and ground-based wave data and interpreted using cold plasma propagation theory. The presence of heavy ions (O⁺, He⁺) dramatically modifies ICW magnetospheric propagation characteristics giving rise to spectral slots and polarization reversals. These properties may be used in plasma diagnostics. Finally satellite-ground correlations and techniques for determining the magnetospheric source position of ICW's not seen at synchronous orbit but observed on the ground as structured Pc1 pulsations are considered.     

The Jovian magnetodisk

Magnetic field measurements made by the vector helium magnetometers on board Pioneers-10 and 11 reveal the existence of a current sheet (thickness 2R _J) carrying an eastward current. Self-consistent studies of the current sheet show that the magnitude of the current is of the order of 10⁺² Am⁺¹ and that the current is carried by a hot (T>1 keV) plasma, the density of which varies between 1 cm⁺³ at 30R _J to 10⁺² cm⁺³ at 80R _J. The current sheet is warped azimuthally and parallel to the magnetic dipole equator.The existence of an azimuthal field component indicates a poloidal plasma flow transporting some 10²⁹ ions per second from Jupiter into the outer magnetosphere. It is shown that, if the outer magnetosphere is in a steady state, this plasma must be transported outward within the current sheet by a diffusion process which is faster than the one responsible for particle transport in the inner magnetosphere but slower than Bohm diffusion. It is suggested that the diffusion is due to the observed mhd turbulence in the current sheet. Such a model requires the existence of open field lines along which particles can escape freely into interplanetary space.Proceedings of the Symposium on Solar Terrestrial Physics held in Innsbruck, May–June 1978.     

A New Mechanism of Coronal Heating

The interaction between network magnetic fields and emerging intranetwork fields may lead to magnetic reconnection and microflares, which generate fast shocks with an Alfvén Mach number M _A<2. Protons and less abundant ions in the solar corona are then heated and accelerated by fast shocks. Our study of shock heating shows that (a) the nearly nondeflection of ion motion across the shock ramp leads to a large perpendicular thermal velocity (v _th), which is an increasing function of the mass/charge ratio; (b) the heating by subcritical shocks with 1.1 M_A 1.5 leads to a large temperature anisotropy with T/T 50 for O⁵⁺ ions and a mild anisotropy with T_/T 1.2 for protons; (c) the large perpendicular thermal velocity of He⁺⁺ and O⁵⁺ ions can be converted to the radial outflow velocity (u) in the divergent coronal field lines; and (d) the heating and acceleration by shocks with 1.1 M_A 1.5 can lead to u(O⁵⁺) v _th(O⁵⁺) 460 km s^–1 for O⁵⁺ ions, u(He⁺⁺) v _th(He⁺⁺) 360 km s^–1 for He⁺⁺ ions, and u(H⁺) v _th(H⁺) 240 km s^–1 for protons at r=3–4 R . Our results can explain recent SOHO observations of the heating and acceleration of protons and heavier ions in the solar corona.     

The Analyzer of Space Plasmas and Energetic Atoms (ASPERA-3) for the Mars Express Mission

The general scientific objective of the ASPERA-3 experiment is to study the solar wind – atmosphere interaction and to characterize the plasma and neutral gas environment with within the space near Mars through the use of energetic neutral atom (ENA) imaging and measuring local ion and electron plasma. The ASPERA-3 instrument comprises four sensors: two ENA sensors, one electron spectrometer, and one ion spectrometer. The Neutral Particle Imager (NPI) provides measurements of the integral ENA flux (0.1–60 keV) with no mass and energy resolution, but high angular resolution. The measurement principle is based on registering products (secondary ions, sputtered neutrals, reflected neutrals) of the ENA interaction with a graphite-coated surface. The Neutral Particle Detector (NPD) provides measurements of the ENA flux, resolving velocity (the hydrogen energy range is 0.1–10 keV) and mass (H and O) with a coarse angular resolution. The measurement principle is based on the surface reflection technique. The Electron Spectrometer (ELS) is a standard top-hat electrostatic analyzer in a very compact design which covers the energy range 0.01–20 keV. These three sensors are located on a scanning platform which provides scanning through 180^∘ of rotation. The instrument also contains an ion mass analyzer (IMA). Mechanically IMA is a separate unit connected by a cable to the ASPERA-3 main unit. IMA provides ion measurements in the energy range 0.01–36 keV/charge for the main ion components H⁺, He⁺⁺, He⁺, O⁺, and the group of molecular ions 20–80 amu/q. ASPERA-3 also includes its own DC/DC converters and digital processing unit (DPU).     

Plasmaspheric Density Structures and Dynamics: Properties Observed by the CLUSTER and IMAGE Missions

Plasmaspheric density structures have been studied since the discovery of the plasmasphere in the late 1950s. But the advent of the Cluster and Image missions in 2000 has added substantially to our knowledge of density structures, thanks to the new capabilities of those missions: global imaging with Image and four-point in situ measurements with Cluster. The study of plasma sources and losses has given new results on refilling rates and erosion processes. Two-dimensional density images of the plasmasphere have been obtained. The spatial gradient of plasmaspheric density has been computed. The ratios between H⁺, He⁺ and O⁺ have been deduced from different ion measurements. Plasmaspheric plumes have been studied in detail with new tools, which provide information on their morphology, dynamics and occurrence. Density structures at smaller scales have been revealed with those missions, structures that could not be clearly distinguished before the global images from Image and the four-point measurements by Cluster became available. New terms have been given to these structures, like “shoulders”, “channels”, “fingers” and “crenulations”. This paper reviews the most relevant new results about the plasmaspheric plasma obtained since the start of the Cluster and Image missions.     

Observations of the interplanetary plasma

Observations bearing on the nature and properties of the interplanetary plasma are reviewed, and consideration is given to possible fruitful directions for further work. The observations are classified according as they involve traditional (comet tail, optical, geomagnetic, cosmic ray), radio (solar noise, radar, radio-source scattering and scintillation, space-probe transmission) or direct (space-probe) measurements. A fairly complete set of references up to September 1967 is given for the cases of comet tail, radar, radio-source scattering and scintillation, and space-probe measurements.An important development concerns observations of the composition of the solar wind. High-resolution measurements of the positive ion energy per charge spectra have been made using the Vela-3 satellites (Bame et al., 1968). Ionic components other than H⁺ and He⁺⁺ have been detected, notably the various ions of oxygen, O⁺⁵, O⁺⁶, O⁺⁷, (Hundhausen et al., 1968). A promising technique for unambiguously distinguishing H⁺ and He⁺⁺ ions, based on velocity as well as energy per unit charge, has been flown successfully on the satellite IMP-F by Ogilvie and Williamson (1968).This research was supported by the Advanced Research Projects Agency (Project DEFENDER) and was monitored by the U.S. Army Research Office — Durham under Contract DA-31-124-ARO-D-257.     

Electric gaps in pulsar magnetospheres

Two contrasting models of the magnetosphere are studied: a classical, quasi-mhd model, in which it is the componentE that accelerates electrons to relativistic energies; and a model with e⁺-e^– production, in which the componentE is locally crucial, both in an acceleration domain near the star and in a dissipation domain beyond the light-cylinder.     

Extreme Ultraviolet Imager Observations of the Structure and Dynamics of the Plasmasphere

The IMAGE Extreme Ultraviolet Imager (EUV) provides our first global images of the plasmasphere by imaging the distribution of He⁺ in its 30.4-nm resonance line. The images reveal the details of a highly structured and dynamic entity. Comparing EUV images and selected in-situ observations has helped to validate the remote sensing measurements. The brightness in the EUV images is heavily weighted by the He⁺ density near the plane of the magnetic equator, but two lines of evidence emphasize that the features seen by EUV extend far from the equator, and in at least some cases reach the ionosphere. Certain features and behaviors, including shoulders, channels, notches, and plasma erosion events, appear frequently in the EUV images. These are keys to understanding the ways that electric fields in the inner magnetosphere affect the large and meso-scale distribution of plasma, and their study can elucidate the mechanisms by which the solar wind and interplanetary magnetic field couple to the inner magnetosphere.     

EXOSAT observations of the bright X-ray source GX9+1

We present the results of the spectral and timing analysis of an observation of GX9+1/4U1758-205 performed with the Medium Energy Experiment aboard EXOSAT. During our observation the source flux varied irregularly in time scales from minutes to hours. No periodic emission in the period range from 16 msec to 2000 sec was found with an upper limit of around 1% (3 ) for the pulsed fraction. The hardness ratio shows a correlated change with the flux intensity (Sco X-1 behaviour). The spectrum could be fitted by a double component model, a black body component (kT=1.16–1.26 keV) together with a thermal bremsstrahlung law (kT=13–15keV). The black-body temperature-black-body flux relation follows a Stefan Boltzmann law with R_BB=15.3 km^*D/10 kpc. No iron line was detected. The upper limit for the line equivalent width of a 6.7 keV iron emission line is 40 eV (1). The X-ray spectral behaviour of GX9+1 indicates, that this source belongs to the class of Low-Mass X-ray Binaries (LMXB).     

The Galileo Energetic Particles Detector

Amongst its complement of particles and fields instruments, the Galileo spacecraft carries an Energetic Particles Detector (EPD) designed to measure the characteristics of particle populations important in determining the size, shape, and dynamics of the Jovian magnetosphere. To do this the EPD provides 4 angular coverage and spectral measurements for Z 1 ions from 20 keV to 55 MeV, for electrons from 15 keV to > 11 MeV, and for the elemental species helium through iron from approximately 10 keV nucl^-1 to 15 MeV nucl^-1. Two bi-directional telescopes, mounted on a stepping platform, employ magnetic deflection, energy loss versus energy, and time-of-flight techniques to provide 64 rate channels and pulse height analysis of priority selected events. The EPD data system provides a large number of possible operational modes from which a small number will be selected to optimize data collection during the many encounter and cruise phases of the mission. The EPD employs a number of safeing algorithms that are to be used in the event that its self-checking procedures indicate a problem. The EPD has demonstrated its operational flexibility throughout the long evolution of the Galileo program by readily accommodating a variety of secondary mission objectives occasioned by the changing mission profile, such as the Venus flyby and the Earth 1 and 2 encounters. To date the EPD performance in flight has been nominal. In this paper we describe the instrument and its operation.