The Electron Beam Instrument (F6) on Freja

The Electron Beam Instrument (F6) onFreja is the first attempt to apply the electron drift technique in a region of large ambient magnetic fields. The paper describes the operational principles, the technical realization, and the difficulties encountered in the derivation of the electric fields.     

Outstanding issues in understanding the dynamics of the inner plasma sheet and ring current during storms and substorms

The paper deals with five selected issues of the dynamical coupling of the near-Earth plasma sheet and magnetosphere, (1) substorm initiation, (2) dipolarization, (3) pressure release of the outer magnetosphere via the auroral energy conversion process, (4) magnetization of the very high beta plasma assembling at the inner edge of the tail, and (5) penetration of energetic particles into the ring current below L 4. One outstanding and strongly debated subject is not discussed here, the origin of the substorm current wedge. The main conclusions (or personal preferences) are: (1) the substorm is initiated by formation of a near-Earth neutral line; (2) dipolarization occurs through magnetic flux transport by the earthward reconnection flow and not by current diffusion; (3) the auroral energy conversion process, the “auroral pressure valve”, contributes substantially to the pressure release during the substorms; (4) high beta ( 10) plasma breaks up into smaller scale blobs under slow magnetization; and (5) deep and prolonged penetration of hot plasma sheet plasma into the middle magnetosphere produces currents and electric fields which lead to the growth of the storm-time ring current.     

Commonalities Between Ionosphere and Chromosphere

Three types of processes, occurring in the weakly ionized plasmas of the Earth’s ionosphere as well as in the solar chromosphere, are being compared with each other. The main objective is to elaborate on the differences introduced primarily by the grossly different magnitudes of the densities, both with respect to the neutral and, even more so, to the plasma constituents. This leads to great differences in the momentum coupling from the plasma to the neutral component and becomes clear when considering the direct electric current component transverse to the magnetic field, called “Pedersen current”; in the ionosphere, which has no quasi-static counterpart in the chromosphere. The three classes of processes are related to the dynamical response of the two plasmas to energy influx from below and from above. In the first two cases, the energy is carried by waves. The third class concerns plasma erosion or ablation in the two respective regions in reaction to the injection of high Poynting and/or energetic particle fluxes.     

Towards a European vision for space exploration: Recommendations of the Space Advisory Group of the European Commission

As a result of increasing public and political interest in ‘space’ (i.e. solar system) exploration at the global scale, the Space Advisory Group of the European Commission has evaluated the situation in Europe with regard to its potential to participate in this ambitious global enterprise. Aspects of science, technology, environment and safety, society, spin-offs and international cooperation were all considered. The group concluded that Europe possesses sufficient key technologies and scientific expertise to play a major role in international space exploration and has recommended that the EU take a central role to ensure the success of future European space exploration, not only to give a clear political signal for the way forward but also to ensure an appropriate financial framework. In this way Europe would embrace the spirit of the European Space Policy and contribute to the knowledge-based society by investing significantly in space-based science and technology, thereby playing a strong role in international space exploration.     

THE ELECTRON DRIFT INSTRUMENT FOR CLUSTER

The Electron Drift Instrument (EDI) measures the drift of a weak beam of test electrons that, when emitted in certain directions, return to the spacecraft after one or more gyrations. This drift is related to the electric field and the gradient in the magnetic field, and these quantities can, by use of different electron energies, be determined separately. As a by-product, the magnetic field strength is also measured. The present paper describes the scientific objectives, the experimental method, and the technical realization of the various elements of the instrument.     

Artifical plasma jet in the ionosphere

The PORCUPINE sounding rocket project provided the opportunity to study the dynamics of an artificially injected plasma beam in the near-Earth space. The structure of the plasma beam, its propagation across the magnetic field as well as the resulting wave phenomena will be discussed.     

The Freja science mission

Freja ^*, a joint Swedish and German scientific satellite launched on october 6 1992, is designed to give high temporal/spatial resolution measurements of auroral plasma characteristics. A high telemetry rate (520 kbits s^–1) and 15 Mbyte distributed on board memories that give on the average 2 Mbits s^–1 for one minute enablesFreja to resolve meso and micro scale phenomena in the 100 m range for particles and 1–10 m range for electric and magnetic fields. The on-board UV imager resolve auroral structures of kilometer size with a time resolution of one image per 6 s. Novel plasma instruments giveFreja the capability to increase the spatial/temporal resolution orders of magnitudes above that achieved on satellites before. The scientific objective ofFreja is to study the interaction between the hot magnetospheric plasma with the topside atmosphere/ionosphere. This interaction leads to a strong energization of magnetospheric and ionospheric plasma and an associated erosion, and loss, of matter from the Terrestrial exosphere.Freja orbits with an altitude of 600–1750 km, thus covering the lower part of the auroral acceleration region. This altitude range hosts processes that heat and energize the ionospheric plasma above the auroral zone, leading to the escape of ionospheric plasma and the formation of large density cavities.     

Cosima – High Resolution Time-of-Flight Secondary Ion Mass Spectrometer for the Analysis of Cometary Dust Particles onboard Rosetta

The ESA mission Rosetta, launched on March 2nd, 2004, carries an instrument suite to the comet 67P/Churyumov-Gerasimenko. The COmetary Secondary Ion Mass Anaylzer – COSIMA – is one of three cometary dust analyzing instruments onboard Rosetta. COSIMA is based on the analytic measurement method of secondary ion mass spectrometry (SIMS). The experiment’s goal is in-situ analysis of the elemental composition (and isotopic composition of key elements) of cometary grains. The chemical characterization will include the main organic components, present homologous and functional groups, as well as the mineralogical and petrographical classification of the inorganic phases. All this analysis is closely related to the chemistry and history of the early solar system. COSIMA covers a mass range from 1 to 3500 amu with a mass resolution m/Δm @ 50% of 2000 at mass 100 amu. Cometary dust is collected on special, metal covered, targets, which are handled by a target manipulation unit. Once exposed to the cometary dust environment, the collected dust grains are located on the target by a microscopic camera. A pulsed primary indium ion beam (among other entities) releases secondary ions from the dust grains. These ions, either positive or negative, are selected and accelerated by electrical fields and travel a well-defined distance through a drift tube and an ion reflector. A microsphere plate with dedicated amplifier is used to detect the ions. The arrival times of the ions are digitized, and the mass spectra of the secondary ions are calculated from these time-of-flight spectra. Through the instrument commissioning, COSIMA took the very first SIMS spectra of the targets in space. COSIMA will be the first instrument applying the SIMS technique in-situ to cometary grain analysis as Rosetta approaches the comet 67P/Churyumov-Gerasimenko, after a long journey of 10 years, in 2014.     

ISEE plasma observations near the subsolar magnetopause

The early ISEE orbits provided the opportunity to study the magnetopause and its environs only a few Earth radii above the subsolar point. Measurements of complete two-dimensional ion and electron distributions every 3 or 12 s, and of three-dimensional distributions every 12 or 48 s by the LASL/MPI instrumentation on both spacecraft allow a detailed study of the plasma properties with unprecedented temporal resolution. This paper presents observations obtained during four successive inbound orbits in November 1977, containing a total of 9 magnetopause crossings, which occurred under widely differing orientations of the external magnetic field. The main findings are: (1) The magnetosheath flow near the magnetopause is characterized by large fluctuations, which often appear to be temporal in nature. (2) Between 0.1 and 0.3R _E outside the magnetopause, the plasma density and pressure often start to gradually decrease as the magnetopause is approached, in conjunction with an increase in magnetic field strength. These observations are in accordance with the formation of a depletion layer due to the compression of magnetic flux tubes. (3) In cases where the magnetopause can be well resolved, it exhibits fluctuations in density, and especially pressure and bulk velocity around average magnetosheath values. The pressure fluctuations are anticorrelated with simultaneous magnetic field pressure changes. (4) In ope case the magnetopause is characterized by substantially displaced electron and proton boundaries and a proton flow direction change from upwards along the magnetopause to a direction tranverse to the geomagnetic field. These features are in agreement with a model of the magnetopause described by Parker. (5) The character of the magnetopause sometimes varies strongly between ISEE-1 and -2 crossings which occur 1 min apart. At times this is clearly the result of highly non-uniform motions. There are also cases where there is very good agreement between the structures observed by the two satellites. (6) In three of the nine crossings no boundary layer was present adjacent to the magnetopause. More remarkably, two of the three occurred while the external magnetic field had a substantial southward component, in clear contradiction to expectations from current reconnection models. (7) The only thick (low-latitude) boundary layer (LLBL) observed was characterized by sharp changes at its inner and outer edges. This profile is difficult to reconcile with local plasma entry by either direct influx or diffusion. (8) During the crossings which showed no boundary layer adjacent to the magnetopause, magnetosheath-like plasma was encountered sometime later. Possible explanations include the sudden formation of a boundary layer at this location right at the time of the encounter, and a crossing of an inclusion of magnetosheath plasma within the magnetosphere. (9) The flow in the LLBL is highly variable, observed directions include flow towards and away from the subsolar point, along the geomagnetic field and across it, tangential and normal to the magnetopause. Some of these features clearly are nonstationary. The scale size over which the flow directions change exceeds the separation distance (several hundred km) of the two spacecraft.