Ion Production Rate Research Articles

Effects of solar variations on the upper atmosphere

Several semi-empirical models of the terrestrial upper atmosphere are presently available. These models take into account solar activity effects by using the solar decimetric flux as an index. Such a procedure is a consequence of the lack of continuous determinations of the solar spectrum directly responsible for the physical structure of the upper atmosphere. Variations of the thermopause temperature are discussed. Using five sets of solar irradiances measured in the ultraviolet and in the extreme ultraviolet, the penetration of solar radiation is analyzed as a function of solar activity. Several examples of absorption profiles and ion production rates are discussed for variable conditions. Various energetic effects are also described. All computations are made for physical conditions above Scheveningen (52.08° N) where the 14th ESLAB symposium was held.

The interaction between plasma and macroparticles in a multi-cathode-spot vacuum arc

The interaction between the interelectrode plasma and macroparticles (droplets) produced by a multitude of cathode spots in a vacuum arc between Cu electrodes is analyzed, using previous experimental measurements of the macroparticle size distribution and erosion rate and a flowing plasma model. The effect of the plasma on the macroparticles is considered by treating the macroparticles as floating probes and calculating the particle, momentum, and energy fluxes to them. It is found that slow macroparticles are significantly deflected form their original trajectories owing to ion bombardment, and that steady-state macroparticle temperatures of 2000–2600 K are obtained from the balance of the energy influx (primarily from ion bombardment) with the evaporative outflux. The effect of the macroparticles on the plasma is considered by calculating the production rate of neutral atoms and ions originating from macroparticle evaporation, by examining the possibility of occlusion of the discharge path by macroparticles, and of cathode-spot formation on detached particles. The calculated neutral density is proportional to J and is in the range 0.02–0.5% of the electron density, depending upon electron temperature and macroparticle velocity. In the 107 A m−2 Cu arc, the calculated neutral density is in the range 1×1017–2.5×1018 m−3. The neutral atoms are eventually ionized and the rate of ion production from the macroparticles can become significant in comparison with that of cathode-spot-produced ions under certain conditions. Occlusion of the discharge path is negligible, and the occurrence of sustained cathode-spot activity on the macroparticles is improbable.

Stellar chromospheres and coronae

view Abstract Citations (28) References (15) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Stellar chromospheres and coronae Athay, R. G. Abstract An attempt is made to provide an updated explanation of the essential structure features of the solar atmosphere based, where possible, on the constraints imposed by the physics of the solar plasma. The chromospheric temperature plateaus are identified with plasma properties determined by the degree of ionization of hydrogen. This is possible because the energy loss is solely by radiation and the nature of the radiation loss changes rather discontinuously as the degree of ionization increases. The ionization conditions are discussed in relation to other stars. In the case of the transition region and the corona, the plasma is essentially fully ionized and, in addition, the role of radiation enters somewhat indirectly. Publication: The Astrophysical Journal Pub Date: November 1981 DOI: 10.1086/159418 Bibcode: 1981ApJ...250..709A Keywords: Chromosphere; Solar Atmosphere; Solar Physics; Solar Wind; Stellar Coronas; Energy Dissipation; Ion Production Rates; Solar Radiation; Solar Temperature; Stellar Models; Stellar Structure; Astrophysics full text sources ADS |

Radio observation of comet Meier /1978f/ in 18-cm OH lines

view Abstract Citations (5) References (17) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Radio observation of comet Meier /1978f/ in 18-cm OH lines Giguere, P. T. ; Huebner, W. F. ; Bania, T. M. Abstract Observations of 18-cm OH spectral lines in comet Meier (1978f) with the 1000-ft. Arecibo telescope show spatial resolution of the OH coma by the 2.9 arcmin beam (=3.7 x 10 to the 5th km). The data agree with predictions of the solar Fraunhofer spectrum-pumping theory of comet OH excitation. On the assumption that the OH parent molecule (e.g., H2O) has a Haser-model scale length of about 1.0 x 10 to the 5th km at heliocentric distance 1 AU, an OH scale length of less than 10 to the 6th km, and probably near 1.0 x 10 to the 5th km is derived. Assuming a recently calculated value of the OH lifetime and the solar radiative pumping model, the results indicate an OH production rate of 10 to the 29th Kayser at heliocentric distance 2 AU. Publication: The Astronomical Journal Pub Date: September 1980 DOI: 10.1086/112797 Bibcode: 1980AJ.....85.1276G Keywords: Comets; Hydroxyl Emission; Line Spectra; Molecular Excitation; Radio Astronomy; Abundance; Astronomical Spectroscopy; Circular Polarization; Hydroxyl Radicals; Ion Production Rates; Normal Density Functions; Radial Velocity; Radiant Flux Density; COMETS; MEIER COMET; RADIO ASTRONOMY; OBSERVATIONS; SPECTRUM; COMAE; MODELS; DATA; PROCEDURE; PRODUCTION RATE; HYDROXYL ION; EMISSIONS; COMPARISONS; DENSITY; ULTRAVIOLET; FLUX; ANALYSIS; WATER; Astronomy; Comets full text sources ADS |

Negative ion production rates in rare gas-halide lasers

This paper reports on dissociative electron attachment in F <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> , NF <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> , Cl <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> , and I <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> . The principle of the method is to produce a short burst of photoelectrons from a photocathode by means of light from an argon-fluoride laser. Subsequently, by studying the motion of electrons and negative ions in a constant electric field ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E</tex> ) region, information is obtained about drift velocities and effective attachment cross sections. Helium, argon, and nitrogen were used as buffer gases. Of particular interest is a very strong temperature dependence of the attachment coefficient in I <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> . Measurements were taken from 35 to 110°C, covering an <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E/N</tex> range of 1-50 Townsend. An explanation based on vibrational excitation is presented.

Ion production and effective loss rate in the mesosphere and lower thermosphere during the Western European Winter Anomaly Campaign 1975/76

As part of a campaign to study the middle latitude ionosphere during winter anomaly conditions, rocket ‘salvoes’ were launched from ‘El Arenosillo’, Spain, on 4 and 21 January 1976. On each of these days the rocket instrumentation measured solar X-ray and H-Lyman-α intensities, energetic particle precipitation, and also the height distribution of the minor constituents NO and O 2( 1Δ g) . On this basis the ion production q( h) in the height range 50–120 km was estimated. The main contribution to q( h) were X-rays (above 90 km), H-Lyman-α (70–90 km), ionization of O 2( 1Δ g (80–90 km), particles, and galactic cosmic rays (below 70 km). Combining the ion production with simultaneously measured values of electron density N ϵ ( h) an estimate of the effective electron loss rate ψ(h) = q N ϵ 2 was obtained. On both days, ψ( h) showed a characteristic rapid decrease from values about 10 −11–10 −10 m 3s −1 below 78 km to values in the range 2 × 10 −13–3 × 10 −12m 3s −1 above this height.

Particle ionization rates from total solar eclipse rocket ion composition results in the South Atlantic Geomagnetic Anomaly

Results available on ion composition and electron densities from the rocket measurements carried out during the total solar eclipse of November 12, 1966, at Cassino, Brazil, are subjected to a detailed numerical analysis using the presently known ion chemistry models for the D and E regions. Solutions of the continuity equations applicable to the individual ionic species are carried out under equilibrium conditions to determine the ion production rates that can best represent the rocket measurements of the ion composition and electron density carried out to represent the full sun conditions. The ion production rates so derived are then inserted in a set of time dependent solutions of the continuity equations to predict the ion density height distribution during the eclipse corresponding to the available rocket measurements. A comparison between the calculated results and the observations during the totality is then made to determine the residual ion production rates in the lower ionosphere, from which the part that cannot be accounted for by solar radiation is attributed to the precipitation of high‐energy particles in the South Atlantic geomagnetic anomaly. The results are discussed in the light of the previous estimates of the ion production rates based on the nighttime occurrence of blanketing type Es in the anomaly region.

Relative yields of ground-state and excited-state ions of Zn, Cd and Hg in thermal-energy charge-transfer reactions of He+ions

The production rates of zinc, cadmium and mercury ions in their ground states, relative to those leading to excited-state formation, in thermal-energy charge-transfer collisions with He+ ions have been measured in a flowing afterglow. In the cases of cadmium and mercury cross sections for ground-state production are very small compared to those for excited-ion production. Although a full analysis of the zinc system cannot yet be carried out, it is likely that a similar result will hold. The results have been explained in terms of pre-emption of the molecular curve crossings in the Landau-Zener model. From this evidence the authors conclude that the present power limitations of the helium-metal-vapour laser are not determined by atomic processes of this type.

Effects of charge exchange involving H and H + in the upper atmosphere

It is argued that there is a terrestrial loss of hydrogen as ions which includes the polar wind but extends effectively down to a latitude in the range 45–50° invariant. In daytime and for much of the night-time the flux is close to the limiting value for H + flow through the topside ionosphere. It is argued that the flux decreases rapidly with increasing solar activity, following the decrease in neutral hydrogen concentration. It has been found that as solar activity increases the Jeans escape flux increases, and the charge exchange escape flux increases until moderate solar activity levels are reached. As solar activity increases from moderate to high levels, the charge exchange escape may decrease again. A new budget for terrestrial hydrogen loss over the solar cycle is given. The global flux of hydrogen ions outward from the ionosphere is comparable with estimates of the plasma sheet loss rates, and this flux, together with some solar wind plasma, is an attractive source for the plasma sheet. The energetic neutrals produced from the charge exchange of ring current ions with thermal-energy neutrals in the exosphere produce the optical emission of the equatorial aurora, which can be related to ion production rates near and above the E-region. The ionization production is adequate to explain the enhancements in ion production observed during magnetic storms at Arecibo.

Negative glow and positive column discharges for helium/metal-vapour lasers-a comparison

The comparative abilities of the negative glow and positive column regions of one and the same helium/zinc discharge to tolerate an increasing density of the metal vapour have been investigated. Spatially resolved profiles of sidelight emission from particular upper laser levels of Zn II were recorded over a wide range of discharge conditions. Evidence that the helium ion production rate can be maintained in the negative glow at pressures of zinc vapour as high as 0.05-0.5 Torr is the undiminished intensity of Zn II levels known to be populated by heavy-body collision processes. The same transitions, excited in the positive column, show a rapid decline in their intensity at zinc vapour pressures above 0.005 Torr. The difference in behaviour is ascribed to the existence, independent of metal vapour density, of a significant tail of high energy electrons in the negative glow electron energy distribution. The factors which determine the optimum partial pressure in the two cases are compared.

Optimum operating conditions for a laser uranium enrichment plant

Operating conditions of the laser uranium enrichment plant to obtain cheaper enriched uranium are optimised by using the standard optimisation procedure. A simple kinetic model is given to obtain the ion production rate as a function of the laser energy density, ultraviolet light energy density, atomic density and depth and height of the reaction region. The unit cost of enriched uranium is chosen as a value function instead of the unit cost of the separative work. The construction cost is expressed by means of an exponential function to take the scale merit into account. Two numerical results are given. In case 1, the laser power and efficiency are subject to the restraints determined by the present technical levels and in case 2, they are free. The unit cost of the enriched uranium is higher than those of the gaseous diffusion and gas centrifuge methods by a factor of 2 ∼ 11. Results indicate that laser uranium enrichment is probably competitive with the other uranium enrichment methods, provided that the laser efficiency is improved by up to 1% and the laser lifetime is extended several times.

Cost analyses of uranium enrichment by laser isotope separation process

The probability of the selective two-step photoionisation of 235U atoms by laser and ultraviolet radiations is estimated from the rate equations for uranium atoms with two isotopes with three levels. The population of 235U ions is obtained by linearising the rate equations. We have calculated the ion production rates for three cases in which the laser and ultraviolet powers are changed while the atom density is kept constant. The power consumption and the capital investment required for the large-scale laser enrichment plant conceptionally designed based upon the above results, and consequently the unit cost of separative work, are estimated. It is concluded that the laser isotope separation process could be competitive with the conventional gaseous diffusion and gas centrifugal methods.

Solar corpuscular emission and neutral chemistry in the Earth's middle atmosphere

The neutral chemistry initiated in the upper stratosphere and mesosphere by solar proton bombardment can significantly alter the concentrations of several minor constituents at high latitudes. Production rates of ions and neutral species due to two large proton events are computed, and their effect on the chemistry of the middle atmosphere is investigated with a time dependent numerical model. The production of odd hydrogen in the mesosphere which results from ion chemistry can reduce the daytime ozone concentration to 75% of its normal value over a limited range of altitude. The diurnal variation of O3 is greatly altered during the particle precipitation. Proton events which cause large ionization and dissociation rates in the upper stratosphere create large amounts of nitric oxide which have a long lifetime before conversion to N2 at these levels. Horizontal transport of this NO to middle latitudes may influence upper stratospheric ozone concentrations on a global scale.

Resonance shifts in the multiphoton ionization of cesium atoms

This work reports the multiphoton ionization of cesium atoms, via resonance with the $6F$ level, by interaction with a single transverse and longitudinal mode neodymium-glass laser beam. At a low rate of ion production, when the laser frequency is tuned through resonance, the laser intensity necessary to create a constant number of ions passes through a minimum, as expected, for a three-photon energy equal to the unperturbed $6S\ensuremath{\rightarrow}6F$ transition energy. But for a higher ionization rate, involving larger laser intensities, a departure from expectation is observed which is interpreted as a consequence of an energy shift of the transition. The level shifts are demonstrated in another way by their strong effect on the experimental order of nonlinearity of the interaction, ${K}_{\mathrm{expt}}$. A sharp variation of ${K}_{\mathrm{expt}}$ is observed when the energy shift of the $6S\ensuremath{\rightarrow}6F$ transition exactly compensates the wavelength detuning of the laser. The latter method gives shift values which are found to be independent of the large variations of the interaction volume under conditions of resonance. Both methods give a linear dependence of the shifts on the laser intensity. Identification of these shifts with energy shifts of the $6S\ensuremath{\rightarrow}6F$ transition is subject to theoretical reservations and needs further experimentation.

Neutral helium emission in Wolf-Rayet envelopes

view Abstract Citations (11) References (12) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Neutral helium emission in Wolf-Rayet envelopes. Oegerle, W. R. ; van Blerkom, D. Abstract A non-LTE analysis of neutral helium emission is performed for Wolf-Rayet stars. The statistical equilibrium equations are derived and simplified by using the escape-probability method. Using a thirty-six-bound-level model helium atom, the relative intensities of allowed transitions are calculated for various helium abundances at electron temperatures of 10,000 and 20,000 K and are compared with observations of MR 119. Publication: The Astrophysical Journal Pub Date: May 1976 DOI: 10.1086/154365 Bibcode: 1976ApJ...206..150O Keywords: Emission Spectra; Helium Atoms; Hot Stars; Radiative Recombination; Stellar Envelopes; Wolf-Rayet Stars; Abundance; Atomic Excitations; Collision Rates; Electron Energy; Equilibrium Equations; Ion Production Rates; Photoionization; Astrophysics full text sources ADS |

Polarization effects in resonant two-photon ionization of caesium

An experiment is reported on two-step photoionization of Cs via the 6P3/2 intermediate state using circularly polarized radiation from a GaAs laser for the first step (8521 AA) and from an Ar-ion laser for the second step. Values for the ratio of ion production rates for right- and left-handed circular polarization in the second step and for the spin polarization of the photoelectrons are presented. The measurements are interpreted on the basis of a calculation which takes into account the hyperfine splitting of the levels involved in the first transition. A description in terms of fine-structure splitting of the 6P state is shown to be totally inadequate, even when allowing for possibly large spin-orbit effects in the continuum. The process is evaluated as a possible source of a spin-polarized electron beam.

On the ionization and excitation of H2O/+/ in comet Kohoutek /1973f/

view Abstract Citations (23) References (79) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS On the ionization and excitation of H2O+ in comet Kohoutek (1973f). Wyckoff, S. ; Wehinger, P. A. Abstract Intensities have been measured for the H20 + A2A1 k2B1 bands in tail spectra of comet Kohoutek within a region of approximately 10 km of the nucleus. Accurate H20 photodecomposition rates have been calculated and H20 ionization rates for solar-wind interactions (electron impact and charge exchange) and gas-phase reactions estimated. The computed lifetime against photodecomposition for cometary H20 molecules at 1 AU is 25 hours. It was Tound that solar La and the solar ultraviolet flux in the region 1450 to 1860 A contribute equally and essentially control the photodissociation of H20 molecules; while the solar Lyman continuum determines the photoionization rate. Excitation rates and relative band intensities for H20 + ions were computed for the processes H20(k1A1) + +( ) + e and H20+(k2B1) + hv H20+(A2A1). The dominant excitation mechanism was shown to be resonance fluorescence. A dominant ionization process could not be determined. Column densities for H20 + ions in the tail at projected nuclear distances, p 10 km, were found to be 1010+1 to 1011+1 for heliocentric distances in the range 0.5. to 0.9 AU; while an upper limit for the H20+ column density on the sunward side of the coma, p > 5 x 10 km, was estimated to be <% 10 +1cm -2 Subject headings: atomic processes - comets - molecular processes Publication: The Astrophysical Journal Pub Date: March 1976 DOI: 10.1086/154210 Bibcode: 1976ApJ...204..616W Keywords: Comet Tails; Kohoutek Comet; Molecular Excitation; Molecular Spectra; Photoionization; Water Vapor; Electron Impact; Fluorescence; Gas Density; Ion Production Rates; Ionization Cross Sections; Photodecomposition; Photodissociation; Solar Wind; Astrophysics full text sources ADS |

Multiple ionization by low-energy cosmic rays and the abundance of highly ionized interstellar atoms

view Abstract Citations (2) References (19) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Multiple ionization by low-energy cosmic rays and the abundance of high ionized interstellar atoms. Watson, W. D. Abstract Calculations are presented and employed in conjunction with available experimental data to estimate cross sections for multiple ionization of atoms by low-energy (MeV/nucleon) cosmic rays. The efficiency of multiple ionization increases rapidly with the charge of the cosmic ray, so that heavier (Z at least 6) nuclei are the dominant contributors for cosmic-ray compositions deduced from higher-energy cosmic rays. Multiple ionization dominates in the production of certain highly ionized atoms by cosmic rays under typical interstellar conditions. N v is considered explicitly, and its production rate by low-energy cosmic rays is estimated to be enhanced by a factor of about 5 to 100. For a low-energy cosmic-ray flux of the proposed intensity for heating and ionizing the interstellar gas, the predicted abundance for N v will be near or above the observed limit if previous calculations are otherwise correct. Publication: The Astrophysical Journal Pub Date: February 1976 DOI: 10.1086/154149 Bibcode: 1976ApJ...204...47W Keywords: Abundance; Atomic Excitations; Cosmic Rays; Gas Ionization; Interstellar Gas; Ion Production Rates; Ionization Cross Sections; Particle Interactions; Radiant Heating; Astrophysics full text sources ADS |

Observations of Comet Kohoutek (1973f) with a Ground-Based Fabry-Perot Spectrometer

Between 1973 December 1 and 1974 February 2, optical emission lines from the gas cloud surrounding comet Kohoutek were observed using a double Fabry-Perot etalon spectrometer at Kitt Peak National Observatory. The spectrometer had a resolving power of 40,000, corresponding to a velocity resolution of about 7.5 km sec-1. With this resolution it was possible to use the cometearth relative velocity to resolve faint cometary Hα λ6563, [01] λ6300 and other emission lines from geocoronal and airglow emissions and to study the cometary line profiles in order to obtain information about the composition, effective temperatures, outflow velocities, and production rates of atoms and ions in the cometary envelope.

A determination ofFregion effective recombination coefficients from the Echo 2 Sounding Rocket Plasma Wave and Particle Measurements

The effective dissociative recombination coefficient is calculated at 140- and 225-km altitude by using the Echo 2 rocket flight data. The density of ambient electrons in the immediate vicinity of the rocket payload was measured by the detection of plasma frequency emissions produced by the injection of 40-keV electrons from the accelerator carried aboard the rocket. Electrostatic analyzers measured the directional intensity of the weak auroral precipitation producing the ionization. Under the assumption of equilibrium conditions the value of α obtained at 140 km was between 1.3 × 10−7 and 1.7 × 10−7 cm³ s−1, depending on the pitch angle distribution of the precipitated auroral electrons used in the calculation of the ion production rate. The recombination coefficient obtained at 225 km varied from 1.2 to 6.2 × 10−9 cm³ s−1. The 140-km values compare favorably with laboratory data and are consistent with previous satellite and rocket measurements. The 225-km values are much less certain in that the data suggest that transport of ionization cannot be ignored at this altitude. Both the 140-km and the 225-km values could be low, due to lack of knowledge of the local spectrum below 0.9 keV.