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Recent results of charge exchange emission from solar system objects observed with the Japanese Suzaku satellite are reviewed. Suzaku is of great importance to investigate diffuse X-ray emission like the charge exchange from planetary exospheres and comets. The Suzaku studies of Earth's exosphere, Martian exosphere, Jupiter's aurorae, and comets are overviewed.
Computer simulations of processes which control the relative abundances of ions in the trapping regions of geospace are compared with observations from discriminating ion detectors. Energy losses due to Coulomb collisions between ions and exospheric neutrals are considered, along with charge exchange losses and internal charge exchanges. The time evolution of energetic ion fluxes of equatorially mirroring ions under radial diffusion is modelled to include geomagnetic and geoelectric fluctutations. Limits to the validity of diffusion transport theory are discussed, and the simulation is noted to contain provisions for six ionic charge states and the source effect on the radiation belt oxygen ion distributions. Comparisons are made with ion flux data gathered on Explorer 45 and ISEE-1 spacecraft and results indicate that internal charge exchanges cause the radiation belt ion charge state to be independent of source charge rate characteristics, and relative charge state distribution is independent of the radially diffusive transport rate below the charge state redistribution zone.
The amount of solar wind absorbed because of charge exchange processes in the dayside ionosheath of Venus is calculated. The calculations suggest the existence of a lower limiting ionopause altitude, below which all solar wind particles are removed from the flow by charge exchange. The cold, slow ions resulting from this interaction are thought to play an important role in building the magnetic barrier observed just outside the ionopause and in creating the dayside 'mantle' and downstream 'penumbra' regions. The total absorption caused by charge exchange is typically 2-5%, although when the solar wind dynamic pressure is very high, it can reach 16%.
Latest and best measurements of physical quantities involved in complete calculation of the charge exchange lifetime of mirroring magnetospheric ions are coalesced and summarized. It is critical that the charge exchange lifetimes for ions be known as accurately as possible in order to apply the charge exchange mechanism to ion phenomena within the earth's magnetosphere.
Giotto Ion Mass Spectrometer/High Energy Range Spectrometer (IMS/HERS) observations of solar wind ions show charge exchange effects and solar wind compositional changes in the coma of comet Halley. As the comet was approached, the He(++) to proton density ratio increased until about 1 hour before closest approach after which time it decreased. Abrupt increases in this ratio were also observed in the beginning and near the end of the so-called Mystery Region (8.6 - 5.5(10)(exp 5) km from the comet along the spacecraft trajectory). These abrupt increases in the density ratio were well correlated with enhanced fluxes of keV electrons as measured by the Giotto plasma electron spectrometer. The general increase and then decrease of the He(++) to proton density ratio is quantitatively consistent with a combination of the addition of protons of cometary origin to the plasma and loss of plasma through charge exchange of protons and He(++). In general agreement with the solar wind proton and He(++) observations, solar wind oxygen and carbon ions were observed to charge exchange from higher to lower charge states with decreasing distance to the comet. The more abrupt increases in the He(++) to proton and the He(++) to O(6+) density ratios in the mystery region require a change in the solar wind ion composition in this region while the correlation with energetic electrons indicates processes associated with the comet.
Explorer 45 measurements during the recovery phase of a moderate magnetic storm have confirmed that the charge exchange decay mechanism can account for the decay of the storm-time proton ring current. Data from the moderate magnetic storm of 24 February 1972 was selected for study since a symmetrical ring current had developed and effects due to asymmetric ring current losses could be eliminated. It was found that after the initial rapid decay of the proton flux, the equatorially mirroring protons in the energy range 5 to 30 keV decayed throughout the L-value range of 3.5 to 5.0 at the charge exchange decay rate calculated by Liemohn. After several days of decay, the proton fluxes reached a lower limit where an apparent equilibrium was maintained, between weak particle source mechanisms and the loss mechanisms, until fresh protons were injected into the ring current region during substorms. While other proton loss mechanisms may also be operating, the results indicate that charge exchange can entirely account for the storm-time proton ring current decay, and that this mechanism must be considered in all studies involving the loss of proton ring current particles.
We have studied the escape of neutral helium from the terrestrial atmosphere through exothermic charge exchange reactions between He(+) ions and the major atmospheric constituents N2, O2 and O. Elastic collisions with the neutral background particles were treated quantitatively using a recently developed kinetic theory approach. An interhemispheric plasma transport model was employed to provide a global distribution of He(+) ions as a function of altitude, latitude and local solar time and for different levels of solar ionization. Combining these ion densities with neutral densities from an MSIS model and best estimates for the reaction rate coefficients of the charge exchange reactions, we computed the global distribution of the neutral He escape flux. The escape rates show large diurnal and latitudinal variations, while the global average does not vary by more than a factor of three over a solar cycle. We find that this escape mechanism is potentially important for the overall balance of helium in the Earth's atmosphere. However, more accurate values for the reaction rate coefficients of the charge exchange reactions are required to make a definitive assessment of its importance.
Presented evidence shows that charge exchanges between xenon ions and calcium atoms may produce an inversion between 5s or 4d and 4p energy levels of calcium ions. The dependence of measured intensity ratios on power input to the xenon plasma indicates that charge exchange pumping of the 5s and 4d levels predominates over electron collisional pumping of these levels.
Ion thrusters can be used in a variety of primary and auxiliary space-propulsion applications. A thruster produces a charge-exchange plasma which can interact with various systems on the spacecraft. The propagation of the charge-exchange plasma is crucial in determining the interaction of that plasma with the spacecraft. This paper compares experimental measurements with computer model predictions of the propagation of the charge-exchange plasma from a 30 cm mercury ion thruster. The plasma potentials, and ion densities, and directed energies are discussed. Good agreement is found in a region upstream of, and close to, the ion thruster optics. Outside of this region the agreement is reasonable in view of the modeling difficulties.
A theoretical model of charge exchange utilizing reasonable potential energy curves and coupling matrix elements in a two state impact parameter calculation is presented.
Relativistic heavy ion charge-exchange reactions yield fragments (Delta-Z = + 1) whose longitudinal momentum distributions are downshifted by larger values than those associated with the remaining fragments (Delta-Z = 1, -2,...). Kinematics alone cannot account for the observed downshifts; therefore, an additional contribution from collision dynamics must be included. In this work, an optical model description of collision momentum transfer is used to estimate the additional dynamical momentum downshift. Good agreement between theoretical estimates and experimental data is obtained.
Charge-exchange reactions for scattering to the continuum are considered in a high-energy multiple scattering model. Calculations for (p,n) and (He-3,H-3) reactions are made and compared with experimental results for C-12, O-16, and Al-27 targets. Coherent effects are shown to lead to an important role for inelastic multiple scattering terms when light projectiles are considered.
The charge exchange of metastable 2D oxygen ions with N2 in the thermosphere is investigated through analysis of N2 (+) measurements and related data obtained by the Atmosphere Explorer-C satellite. The rate coefficient for the charge exchange process is found to be 5 + or - 1.7 times 10 to the negative 10th power cu cm per sec. A rate coefficient is also developed for atomic oxygen quenching of the metastable 2D oxygen ions.
This document addresses extreme ultraviolet radiation and X-ray emissions from comets, planets and heliospheric gases focusing on the measurement of charge-exchange cross sections and radiative lifetimes. Highly-charged heavy ions present in the solar wind, and their abundance relative to the total oxygen-ion abundance are detailed. The plan for the Jet Propulsion Laboratory high-charge ion facility is outlined detailing its ability to measure absolute collisional excitation cross sections, absolute charge-exchange cross sections, lifetimes of metastable ion levels, and X-ray emission spectra following charge changes.
A model describing the charge exchange plasma and its propagation is discussed, along with a computer code based on the model. The geometry of an idealized spacecraft having an ion thruster is outlined, with attention given to the assumptions used in modeling the ion beam. Also presented is the distribution function describing charge exchange production. The barometric equation is used in relating the variation in plasma potential to the variation in plasma density. The numerical methods and approximations employed in the calculations are discussed, and comparisons are made between the computer simulation and experimental data. An analytical solution of a simple configuration is also used in verifying the model.
The equatorial pitch-angle distributions of ring-current ions observed during a storm recovery phase at L values between 3 and 4 are compared with the pitch-angle distributions predicted by proton charge exchange with neutral hydrogen. Large disagreements are found, and three alternative explanations are explored. (1) A strong proton source acts to mask the effects of charge exchange. It is believed that the required strong continual source with a unique pitch-angle and energy dependence is unrealistic at these low L values. (2) Presently accepted neutral hydrogen density models have densities well over an order of magnitude too large for a storm recovery phase. No evidence is known to support the required large errors in the densities. (3) The ring current at particle energies not exceeding 50 keV was dominated by some ion species other than protons during the storm recovery phase. Such ions must have much longer lifetimes for charge exchange with hydrogen than do protons. This alternative is strongly favored, with He(+) being an attractive candidate.
The use of high voltage solar arrays greatly reduces or eliminates power processing requirements in space electric propulsion systems. This use also requires substantial areas of solar array to be at high positive potential relative to space and most of the spacecraft. The charge exchange plasma conducts electrons from the ion beam to such positive surfaces, and thereby electrically load the high voltage solar array. To evaluate this problem, the charge-exchange plasma generated by an ion beam was investigated experimentally. Based upon the experimental data, a simple model was derived for the charge-exchange plasma. This model is conservative in the sense that both the electron/ion density and the electron current density should be equal to, or less than, the preducted value for all directions in the hemisphere upstream of the ion beam direction. Increasing the distance between a positive potential surface (such as a high voltage solar array) and the thruster is the simplest way to control interactions. Both densities and currents vary as the inverse square of this distance.
Upper-limit charge exchange cross sections are calculated for Hg(+) on Mo and Cs(+) on Al. The cross sections are calculated from the polarization interaction at low ion energies (1 to 500 eV) and by assuming favorable curve crossings with a hard-core reaction radius at higher energies (500 eV to 10 keV). The cross sections for Hg(+) on Mo becomes greater than corresponding Hg Hg(+) resonance values at ion energies below 2 eV, whereas the Cs(+) Al values remain considerably lower than the Cs(+)Cs resonance value at all ion energies. It is also shown that charge exchange of slow Hg(+) with Mo may be important for spacecraft with electron bombardment thrusters.