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NASA NTRS2000

Using Model-Based Reasoning for Autonomous Instrument Operation

Multiprobe missions are an important part of NASA's future: Cluster, Magnetospheric Multi Scale, Global Electrodynamics and Magnetospheric Constellation are representatives from the Sun-Earth Connections Theme. To make such missions robust, reliable, and affordable, ideally the many spacecraft of a constellation must be at least as easy to operate as one spacecraft is today. To support this need for scalability, science instrumentation must become increasingly easy to operate, even as this same instrumentation becomes more capable and advanced. Communication and control resources will be at a premium for future instruments. Many missions will be out of contact with ground operators for extended periods either to reduce operations cost or because of orbits that limit communication to weekly perigee transits. Autonomous capability is necessary if such missions are to effectively achieve their operational objectives. An autonomous system is one that acts given its situation in a mission appropriate manner without external direction to achieve mission goals. To achieve this capability autonomy must be built into the system through judicious design or through a built-in intelligence that recognizes system state and manages system response. To recognize desired or undesired system states, the system must have an implicit or explicit understanding of its expected states given its history and self observations. The systems we are concerned with, science instruments, can have stringent requirements for system state knowledge in addition to requirements driven by health and safety concerns. Without accurate knowledge of the system state, the usefulness of the science instrument may be severely limited. At the same time, health and safety concerns often lead to overly conservative instrument operations further reducing the effectiveness of the instrument. These requirements, coupled with overall mission requirements including lack of communication opportunities and tolerance of environmental hazards, frame the problem of constructing autonomous science instruments. we are developing a model of the Low Energy Neutral Atom instrument (LENA) that is currently flying on board the Imager for Magnetosphere-to-Aurora Global Exploration (IMAGE) spacecraft. LENA is a particle detector that uses high voltage electrostatic optics and time-of-flight mass spectrometry to image neutral atom emissions from the denser regions of the Earth's magnetosphere. As with most spacecraft borne science instruments, phenomena in addition to neutral atoms are detected by LENA. Solar radiation and energetic particles from Earth's radiation belts are of particular concern because they may help generate currents that may compromise LENA's long term performance. An explicit model of the instrument response has been constructed and is currently in use on board IMAGE to dynamically adapt LENA to the presence or absence of energetic background radiations. The components of LENA are common in space science instrumentation, and lessons learned by modelling this system may be applied to other instruments. This work demonstrates that a model-based approach can be used to enhance science instrument effectiveness. Our future work involves the extension of these methods to cover more aspects of LENA operation and the generalization to other space science instrumentation.

Johnson, Mike↗
NASA NTRS2003

Modeling Variability of Plasma Conditions in the Io Torus

Telescopic observations an in situ measurements of the Io plasma torus show the density, temperature and composition to vary over time, sometimes up to a factor of 2. While previous models of the physical and chemical processes in the Io plasma torus have reasonably modeled the conditions of the Voyager 1 era, their authors have not addressed the observed variability nor explored the sensitivity of torus conditions to input parameters. In this paper we present a homogeneous torus model parameterized by five variables (transport timescale, neutral source strength, ratio of oxygen sulfur to atoms in the source, fraction of superthermal electrons, temperature of these hot electrons). The model incorporates the most recent data for ionization, recombination, charge exchange and radiative energy losses for the major torus species (S, S(sup +), S(sup ++), S(sup +++), O, O(sup +), O(sup ++). We solve equations of conservation of mass and energy to find equilibrium conditions for a set of input parameters. We compare model plasma conditions with those observed by Voyager 1 Voyager 2, and Cassini. Furthermore, we explore the sensitivity of torus conditions to each parameter. We find that (1) torus conditions are distinctly different for the Voyager 1, Voyager 2 and Cassini eras, (2) unique torus input parameters for any given era are poorly constrained given the wide range of solution space that is consistent with the range of observed torus conditions, (3) ion composition is highly sensitive to the specification of a non-thermal electron distribution, (4) neutral O/S source ratio is highly variable with model values ranging between 1.7 for Cassini to 4.0 for Voyager 1 conditions, (5) transport times range between 23 days for Voyager 2 to 50 days for Voyager 1 and Cassini, (6) neutral source strengths range between 7 to 30 x 10(sup -4) cm (sup -3) s(sup -1) which corresponds to a net production of 0.4 to 1.3 tons/s for a torus volume of 1.4 x 10(sup 31) cm(sup 3), or 38 R(sub j)(sup 3).

Delamere, P. A.↗
NASA NTRS1994

The ionization of the diffuse ionized gas

The diffuse ionized gas (DIG), responsible for producing the faint but pervasive H(sub alpha), requires 15% of the power of all Galactic O stars for its ionization. No other source of ionization seems practical. The spectrum is strong in low stages of ionization (N II, SII), weak in (O III), and very weak in (O I) lambda 6300, at least in one well-observed direction, all significantly different from denser H II regions. We give low-density, low-excitation photoionization models that explain the observed spectrum. The lambda 6300 observation eliminates the simplest models for the DIG (Mathis 1986), in which neutral H extends beyond the edge of the very dilute stellar radiation field. Our present models include two components. One, representing the edges of interstellar H I clouds, extends to the point where H becomes neutral. In the second, the fraction of H(sup o) is not allowed to exceed 0.05 to 0.1. Both have very low values of the ionization parameter, or ratio of the number densities of ionizing photons to electrons. The ionization parameter required by our models is shown to be compatible with observed values of photon and electron densities in the diffuse interstellar medium. Interstellar dust is not important in either model. Predictions of the model are that the Galaxy is leaking about 4% of the ionizing radiation of at least the local O stars into the intergalactic medium, that (O II) lambda 3727 approximately equals 1.1 H(sub alpha), and that He(sup +)/H (sup +)) approximately equals 0.6 He/H. A major difficul ty of this picture is having ionizing radiation propagate from the ionizing stars in the plane of the Galaxy to the DIG. We suggest, as do Miller & Cox (1993), that the ionizing radiation from O stars produces holes or tunnels in the distribution of neutral H as seen from their positions, while we see a sky covered with H I sheets or filaments because we are not near a source of ionizing radiation. With our models, several interfaces between ionized and neutral gas are allowed before the observational limit on lambda 6300 is exceeded. Another difficulty is the gas-phase N(S(sup +))/N(H(sup o)) ratio toward the high-latitude star HD 93521 (Spitzer & Fitzpatrick 1993). We require (S/H) to be somewhat lower than solar, either because of depletion onto grains or a Galactic abundance gradient, so that the S(sup +) can be produced in each of separate H(sup o) and H(sup +) regions.

Domgorgen, H.↗
NASA NTRS1998

Profile Evolution Simulation in Etching Systems Using Level Set Methods

Semiconductor device profiles are determined by the characteristics of both etching and deposition processes. In particular, a highly anisotropic etch is required to achieve vertical sidewalls. However, etching is comprised of both anisotropic and isotropic components, due to ion and neutral fluxes, respectively. In Ar/Cl2 plasmas, for example, neutral chlorine reacts with the Si surfaces to form silicon chlorides. These compounds are then removed by the impinging ion fluxes. Hence the directionality of the ions (and thus the ion angular distribution function, or IAD), as well as the relative fluxes of neutrals and ions determines the amount of undercutting. One method of modeling device profile evolution is to simulate the moving solid-gas interface between the semiconductor and the plasma as a string of nodes. The velocity of each node is calculated and then the nodes are advanced accordingly. Although this technique appears to be relatively straightforward, extensive looping schemes are required at the profile corners. An alternate method is to use level set theory, which involves embedding the location of the interface in a field variable. The normal speed is calculated at each mesh point, and the field variable is updated. The profile comers are more accurately modeled as the need for looping algorithms is eliminated. The model we have developed is a 2-D Level Set Profile Evolution Simulation (LSPES). The LSPES calculates etch rates of a substrate in low pressure plasmas due to the incident ion and neutral fluxes. For a Si substrate in an Ar/C12 gas mixture, for example, the predictions of the LSPES are identical to those from a string evolution model for high neutral fluxes and two different ion angular distributions.(2) In the figure shown, the relative neutral to ion flux in the bulk plasma is 100 to 1. For a moderately isotropic ion angular distribution function as shown in the cases in the left hand column, both the LSPES (top row) and rude's string method (bottom row) predict tapered profiles. The LSPES uses an AD with a FWHM = 13.5 degrees, and rude's model uses a ratio of sheath voltage to ion temperature of 50. The more anisotropic IADs produce profiles with more vertical sidewalls and a wider bottom surface, as shown in the right hand column. Here, the LSPES has an AD with a FWHM = 2 degrees, and rude's model uses a ratio of 500 of sheath voltage to ion temperature. The agreement between the LSPES and rude's model is excellent in both cases. We will present etching profiles generated by the LSPES, including calculations of the re-emitted fluxes of both neutrals and ions off of the profile walls. In addition, we will show the effect of geometric structures (overhangs, etc.) on the etching profiles. Other physical aspects, such as surface diffusion, will also be included in the model.

Hwang, Helen H.↗
NASA NTRS1991

The Marshall Engineering Thermosphere model atmosphere Statistical Analysis Mode (MET-SAM)

The minimum, mean, and maximum exospheric temperature on the globe were calculated for every three hour period from 1947 through 1989 using the algorithms in the Marshall Engineering Thermosphere (MET) model and the appropriate solar activity input parameters. Cumulative percent frequency (CPF) distributions were then calculated for each of these temperatures at five levels of solar activity as defined by the 13-month smoothed values of the 10.7-cm solar radio noise flux. Next, the 50, 95, 97.7, and 100 percentile temperature values in each of these five levels of solar activity were curve fit as a function of the 13-month smoothed 10.7-cm flux. The resulting algorithms are used to compute the exospheric temperature in the MET model instead of the technique developed by Jacchia in his 1970 model. These temperatures are then used to enter tables to determine the total mass density and/or the atomic oxygen number density for application to engineering problems. Users can specify the risk level they are willing to accept in the results of analyses that require neutral atmosphere parameters inputs. The model eliminates the guess work in how to combine the solar activity input parameters to insure that the results provide answers at the proper risk levels.

Smith, Robert E.↗
NASA NTRS1994

A model of Triton's role in Neptune's magnetosphere

Escape of neutral hydrogen (H) and nitrogen (N) from Triton's maintains a large neutral cloud, called the Triton torus, in Neptune's magnetosphere. We have developed the first detailed Monte Carlo simulation model of the Triton torus that includes the collisionality, the complex geometry, the injection of two neutral species from Triton (H and N), and the combined effects of photoionization, electron impact ionization, and charge exchange. Ionization in Neptune's plasma sheet was modeled using Voyager plasma observations. Collisions cause both the H and N neutral clouds to become more radially extended, both toward Neptune and out beyond the magnetopause, as well as more extended in latitude, when compared with collisionless models. Moreover, collisions of H with the much more massive N greatly enhance the collisional ejection of H from the system and into Neptune's atmosphere. This effect decreases the probability of H ionization within the magnetosphere relative to that for N, and furthermore causes model results for two-species injection from Triton to differ significantly from those for H injection alone. For a hydrogen escape rate from Triton of 5 x 10(exp 25)/s, as given by photo-chemical models of Triton's upper atmosphere, a nitrogen escape rate of 5 x 10(exp 24)/s gives proton and N(+) sources of 5.6 x 10(exp 24)/s and 3.3 x 10(exp 24)/s, respectively, whose ratio is close to the observed ratio of protons to heavies. A nitrogen escape rate of 2 x 10(exp 25)/s, yields an N(+) source more than twice that of protons, inconsistent with the Voyager data.

Decker, R. B.↗
NASA NTRS2004

Effects of Kinetic Processes in Shaping Io's Global Plasma Environment: A 3D Hybrid Model

The global dynamics of the ionized and neutral components in the environment of Io plays an important role in the interaction of Jupiter's corotating magnetospheric plasma with Io. The stationary simulation of this problem was done in the MHD and the electrodynamics approaches. One of the main significant results from the simplified two-fluid model simulations was a production of the structure of the double-peak in the magnetic field signature of the I0 flyby that could not be explained by standard MHD models. In this paper, we develop a method of kinetic ion simulation. This method employs the fluid description for electrons and neutrals whereas for ions multilevel, drift-kinetic and particle, approaches are used. We also take into account charge-exchange and photoionization processes. Our model provides much more accurate description for ion dynamics and allows us to take into account the realistic anisotropic ion distribution that cannot be done in fluid simulations. The first results of such simulation of the dynamics of ions in the Io's environment are discussed in this paper.

Lipatov, Alexander S.↗
NASA NTRS2024

The Global Mapping of Electron Precipitation and Ionospheric Conductance From Whistler-Mode Chorus Waves

Auroral precipitation is the second major energy source after solar irradiation that ionizes the Earth’s upper atmosphere. Diffuse electron aurora caused by wave-particle interaction in the inner magnetosphere (L < 8) takes over 60% of total auroral energy flux, strongly contributing to the ionospheric conductance and thus to the ionosphere-thermosphere dynamics. This paper quantifies the impact of chorus waves on the diffuse aurora and the ionospheric conductance during quiet, medium, and strong geomagnetic activities, parameterized by AE <100, 100 < AE < 300, and AE > 300, respectively. Using chorus wave statistics and inner-magnetosphere plasma conditions from Timed History Events and Macroscale Interactions during Substorms (THEMIS) observations, we directly derive the energy spectrum of diffuse electron precipitation under quasi-linear theory. We then calculate the height-integrated conductance from the wave-driven aurora spectrum using the electron impact ionization model of Fang et al. (Geophys. Res. Lett., 2010, 37) and the MSIS atmosphere model. By utilizing Fang’s ionization model, the US Naval Research Laboratory Mass Spectrometer and Incoherent Scattar Radar (NRLMSISE-00) model from 2000s for the neutral atmosphere components, and the University of California, Los Angeles (UCLA) Full Diffusion Code, we improve upon the standard generalization of Maxwellian diffuse electron precipitation patterns and their resulting ionosphere conductance. Our study of global auroral precipitation and ionospheric conductance from chorus wave statistics is the first statistical model of its kind. We show that the total electron flux and conductance pattern from our results agree with those of Ovation Prime model over the pre-midnight to post-dawn sector as geomagnetic activity increases. Our study examines the relative contributions of upper band chorus (UBC) and lower band chorus wave (LBC) driven conductance in the ionosphere. We found LBC waves drove diffuse electron precipitation significantly more than UBC waves, however it is possible that THEMIS data may have underestimated the upper chorus band wave observations for magnetic latitudes below 65 degrees. ° .

diffuse auroral precipitation↗
NASA NTRS1988

Constraints on the neutral hydrogen corona at Uranus from its interaction with magnetospheric plasma

Models of collisional reactions between the hot (several keV) protons and neutral atomic hydrogen corona observed at Uranus by Voyager 2 are compared with observations in order to deduce constraints on the coronal density. An upper limit is found for n sub H (5R sub U) of several tens of H/cu cm on the sunward side of Uranus and several H/cu cm on the dark side. The possibility that the hot plasma population might arise from photoionization and electron impact ionization of coronal and interstellar medium hydrogen in the magnetotail, followed by pickup and energization while convecting toward Uranus, is examined and rejected.

Herbert, Floyd↗
NASA NTRS2008

Tungsten and Barium Transport in the Internal Plasma of Hollow Cathodes

The effect of tungsten erosion, transport and redeposition on the operation of dispenser hollow cathodes was investigated in detailed examinations of the discharge cathode inserts from an 8200 hour and a 30,352 hour ion engine wear test. Erosion and subsequent re-deposition of tungsten in the electron emission zone at the downstream end of the insert reduces the porosity of the tungsten matrix, preventing the flow of barium from the interior. This inhibits the interfacial reactions of the barium-calcium-aluminate impregnant with the tungsten in the pores. A numerical model of barium transport in the internal xenon discharge plasma shows that the barium required to reduce the work function in the emission zone can be supplied from upstream through the gas phase. Barium that flows out of the pores of the tungsten insert is rapidly ionized in the xenon discharge and pushedback to the emitter surface by the electric field and drag from the xenon ion flow. Thisbarium ion flux is sufficient to maintain a barium surface coverage at the downstream endgreater than 0.6, even if local barium production at that point is inhibited by tungsten deposits. The model also shows that the neutral barium pressure exceeds the equilibrium vapor pressure of the impregnant decomposition reaction over much of the insert length,so the reactions are suppressed. Only a small region upstream of the zone blocked by tungsten deposits is active and supplies the required barium. These results indicate that hollowcathode failure models based on barium depletion rates in vacuum dispenser cathodes are very conservative.

Hollow cathodes↗
NASA NTRS2009

Barium Depletion in Hollow Cathode Emitters

The effect of tungsten erosion, transport and redeposition on the operation of dispenser hollow cathodes was investigated in detailed examinations of the discharge cathode inserts from an 8200 hour and a 30,352 hour ion engine wear test. Erosion and subsequent re-deposition of tungsten in the electron emission zone at the downstream end of the insert reduces the porosity of the tungsten matrix, preventing the ow of barium from the interior. This inhibits the interfacial reactions of the barium-calcium-aluminate impregnant with the tungsten in the pores. A numerical model of barium transport in the internal xenon discharge plasma shows that the barium required to reduce the work function in the emission zone can be supplied from upstream through the gas phase. Barium that flows out of the pores of the tungsten insert is rapidly ionized in the xenon discharge and pushed back to the emitter surface by the electric field and drag from the xenon ion flow. This barium ion flux is sufficient to maintain a barium surface coverage at the downstream end greater than 0.6, even if local barium production at that point is inhibited by tungsten deposits. The model also shows that the neutral barium pressure exceeds the equilibrium vapor pressure of the impregnant decomposition reaction over much of the insert length, so the reactions are suppressed. Only a small region upstream of the zone blocked by tungsten deposits is active and supplies the required barium. These results indicate that hollow cathode failure models based on barium depletion rates in vacuum dispenser cathodes are very conservative.

plasma discharges↗
NASA NTRS1999

Large Eddy Simulation of Aircraft Wake Vortices in a Homogeneous Atmospheric Turbulence: Vortex Decay and Descent

The effects of ambient turbulence on decay and descent of aircraft wake vortices are studied using a validated, three-dimensional: large-eddy simulation model. Numerical simulations are performed in order to isolate the effect of ambient turbulence on the wake vortex decay rate within a neutrally-stratified atmosphere. Simulations are conducted for a range of turbulence intensities, by injecting wake vortex pairs into an approximately homogeneous and isotropic turbulence field. The decay rate of the vortex circulation increases clearly with increasing ambient turbulence level, which is consistent with field observations. Based on the results from the numerical simulations, simple decay models are proposed as functions of dimensionless ambient turbulence intensity (eta) and dimensionless time (T) for the circulation averaged over a range of radial distances. With good agreement with the numerical results, a Gaussian type of vortex decay model is proposed for weak turbulence: while an exponential type of Tortex decay model can be applied for strong turbulence. A relationship for the vortex descent based on above vortex decay model is also proposed. Although the proposed models are based on simulations assuming neutral stratification, the model predictions are compared to Lidar vortex measurements observed during stable, neutral, and unstable atmospheric conditions. In the neutral and unstable atmosphere, the model predictions appear to be in reasonable agreement with the observational data, while in the stably-stratified atmosphere, they largely underestimate the observed circulation decay with consistent overestimation of the observed vortex descent. The underestimation of vortex decay during stably-stratified conditions suggests that stratification has an important influence on vortex decay when ambient levels of turbulence are weak.

Han, Jongil↗
NASA NTRS1975

Implications of observed charge states of low-energy solar cosmic rays

Recent measurements of the charge states of low-energy (about 100 keV/nucleon) solar cosmic rays at 1 AU are discussed. The measurements are consistent with models involving charge equilibrium with neutral matter at the sun only if the particles lose about 90% of their energy owing to adiabatic deceleration in the solar wind. Such an energy loss is shown to be possible only if the diffusion coefficient for 1-MeV/nucleon particles is smaller than 100 quintillion sq cm per sec. The implications of these results for models of solar-cosmic-ray acceleration are discussed.

Jokipii, J. R.↗
NASA NTRS1991

Data analysis and interpretation related to space system/environment interactions at LEO altitude

Several studies made on the interaction of active systems with the LEO space environment experienced from orbital or suborbital platforms are covered. The issue of high voltage space interaction is covered by theoretical modeling studies of the interaction of charged solar cell arrays with the ionospheric plasma. The theoretical studies were complemented by experimental measurements made in a vacuum chamber. The other active system studied was the emission of effluent from a space platform. In one study the emission of plasma into the LEO environment was studied by using initially a 2-D model, and then extending this model to 3-D to correctly take account of plasma motion parallel to the geomagnetic field. The other effluent studies related to the releases of neutral gas from an orbiting platform. One model which was extended and used determined the density, velocity, and energy of both an effluent gas and the ambient upper atmospheric gases over a large volume around the platform. This model was adapted to study both ambient and contaminant distributions around smaller objects in the orbital frame of reference with scale sizes of 1 m. The other effluent studies related to the interaction of the released neutral gas with the ambient ionospheric plasma. An electrostatic model was used to help understand anomalously high plasma densities measured at times in the vicinity of the space shuttle orbiter.

Raitt, W. John↗
NASA NTRS1975

Phase and amplitude relationships of wave structure observed in the lower thermosphere

Data from the Atmosphere Explorer-C satellite clearly exhibit wavelike variations in neutral composition, ion density, and electron temperature, which appear to be a general feature of the atmosphere. The neutral constituents do not exhibit uniform wave characteristics since the density variations of argon are approximately twice those of molecular nitrogen and helium structure has about one-half the amplitude of the N2 variation. The waves evident in the ion density are nearly in phase with the heavy neutrals, while the electron-temperature variations are predominantly out of phase with those in the ion density. A simple model is suggested to explain the neutral composition results, wherein the enhancements in the major gas densities are in phase with the vertical component of the perturbation velocity of the gas. The vertical velocity modifies the composition by transporting parcels of air to higher or lower regions where the composition is different. The phase relationship between density and velocity implies phase velocities (assuming that these are gravitational waves) of the order of 500 meters per sec.

Reber, C. A.↗
NASA NTRS1984

The global distribution of thermospheric odd nitrogen for solstice conditions during solar cycle minimum

A two-dimensional model of odd nitrogen in the thermosphere and upper mesosphere is described. The global distributions of nitric oxide and atomic nitrogen are calculated for the solstice period for quiet and moderate magnetic activity during the solar minimum period. The effect of thermospheric transport by winds is investigated along with the importance of particle-induced ionization in the auroral zones. The results are compared with rocket and satellite measurements, and the sensitivity of the model to eddy diffusion and neutral winds is investigated. Downward fluxes of NO into the mesosphere are given, and their importance for stratospheric ozone is discussed. The results show that the summer-to-winter pole meridional circulation transports both NO and N(S-4) across the solar terminator into the polar night region where there is a downward vertical transport toward the mesosphere. The model shows that odd nitrogen densities at high winter latitudes are entirely controlled by particle precipitation and transport processes.

Gerard, J.-C.↗
NASA NTRS2024

Storm-Time Variability of Terrestrial Hydrogen Exosphere: Kinetic Simulation Results

Recent studies of TWINS Lyman-α observations have reported an increase in geocoronal column brightness during geomagnetic storms, indicating enhanced exospheric hydrogen atom density (NH). This suggests a complex role of exospheric neutrals in determining storm-time magnetosphere dynamics and their energy release through charge-exchange processes. We developed a Model for Analyzing Terrestrial Exosphere (MATE) to investigate storm-time exospheric behaviors and their physical drivers. MATE traces test hydrogen atoms backward in time from locations in the exosphere to a nominal exobase altitude of 500 km, employing Newtonian mechanics with gravitational force. The model then calculates the phase-space densities (PSDs) of test hydrogen atoms at the exobase using the Maxwellian distribution with physics-based exobase conditions from the TIMEGCM upper atmosphere model. MATE maps PSDs at the exobase to the exosphere using Liouville’s Theorem under collisionless assumptions and derives NH by integrating the PSDs across velocity space. We conducted MATE simulation before, during, and after a minor geomagnetic storm from 12 to 18 June 2008, and compared the model results with NH estimates from the TWINS geocorona data. MATE reproduces storm-time density enhancements soon after the minimum Dst is reached, matching well with a general trend of TWINS NH estimates. The results suggest that upper atmospheric heating during a geomagnetic storm increases the number of ballistic and escaping hydrogen atoms entering the exosphere from the exobase, thereby boosting NH. However, the magnitude of modeled NH mismatches the TWINS NH estimates. The potential mechanisms of this density discrepancy include the physics excluded in the MATE model — such as neutralneutral collisions, neutral-plasma charge exchange, solar radiation pressure, and photoionization — as well as the higher exobase hydrogen density of TIMEGCM compared to typical empirical values, which will be addressed in future.

Hyunju K Connor↗
NASA NTRS2006

Effects of Kinetic Processes in Shaping Io's Global Plasma Environment: A 3D Hybrid Model

The global dynamics of the ionized and neutral gases in the environment of Io plays an important role in the interaction of Jupiter s corotating magnetospheric plasma with Io. Stationary simulations of this problem have already been done using the magnetohydrodynamics (MHD) and the electrodynamics approaches. One of the major results of recent simplified two-fluid model simulations [Saur, J., Neubauer, F.M., Strobel, D.F., Summers, M.E., 2002. J. Geophys. Res. 107 (SMP5), 1-18] was the production of the structure of the double-peak in the magnetic field signature of the Io flyby. These could not be explained before by standard MHD models. In this paper, we present a hybrid simulation for Io with kinetic ions and fluid electrons. This method employs a fluid description for electrons and neutrals, whereas for ions a particle approach is used. We also take into account charge-exchange and photoionization processes and solve self-consistently for electric and magnetic fields. Our model may provide a much more accurate description for the ion dynamics than previous approaches and allows us to account for the realistic anisotropic ion velocity distribution that cannot be done in fluid simulations with isotropic temperatures. The first results of such a simulation of the dynamics of ions in Io s environment are discussed in this paper. Comparison with the Galileo IO flyby results shows that this approach provides an accurate physical basis for the interaction and can therefore naturally reproduce all the observed salient features.

Lipatov, Alexander S.↗