Calculated Ionization Rate Research Articles

Mesospheric ozone depletion during the Solar Proton Event of July 13, 1982 Part II. Comparison between theory and measurements

The solar proton event of July 13, 1982 was the largest to date in the current solar cycle. Proton fluxes observed by the NOAA‐6 satellite have been used to calculate ionization rates during the event, which have been found to be almost as large as those of the August, 1972 event near 70 km, but much smaller at lower altitudes. This ionization leads to the production of odd hydrogen radicals (H+OH+HO2) which catalytically destroy odd oxygen in the mesosphere and stratosphere. A one‐dimensional time‐dependent model has been used to calculate the percentage change in ozone resulting from this event. The calculated ozone depletion is compared to that observed by the Solar Mesosphere Explorer (SME) satellite.

Auroral plasma lines: A first comparison of theory and experiment

In this preliminary report on low‐energy (0.3 to 3 eV) secondary electrons in the auroral E layer (90 to 150 km), we compare intensities of plasma lines observed with the Chatanika radar to theoretical predictions obtained from a detailed numerical model. The model calculations are initiated with a flux of energetic auroral primary electrons which enter the atmosphere and lose energy to electrons, ions, and neutrals through a combination of elastic and inelastic collisions. This flux is chosen in order that the total calculated ionization rate matches one that is deduced from the radar measurements. From these same calculations the steady state secondary electron flux is deduced as a function of altitude, energy, and pitch angle. This flux is used to calculate plasma line intensities which are then compared with observed intensities. Initial comparisons suggest that the plasma line theory, when applied to low altitudes, must include the effect of electron‐neutral collisions. When this is done, the good agreement obtained between theory and experiment indicates the promise of this approach for the study of low‐energy auroral electrons.

Non-Maxwellian velocity distribution functions associated with steep temperature gradients in the solar transition region

Non-Maxwellian electron velocity distribution functions, previously computed for Dupree's model of the solar transition region are used to calculate ionization rates for ions of carbon, nitrogen, and oxygen. Ionization equilibrium populations for these ions are then computed and compared with similar calculations assuming Maxwellian distribution functions for the electrons. The results show that the ion populations change (compared to the values computed with a Maxwellian) in some cases by several orders of magnitude depending on the ion and its temperature of formation.

Nighttime ionization by energetic particles at Wallops Island in the altitude region 120 to 200 km

Five Nike Apache rockets, each including an energetic particle spectrometer and an electron density‐electron temperature experiment, have been launched from Wallops Island (L = 2.6) near midnight under varying geomagnetic conditions. On the most recent of these (5 January 1978) an additional spectrometer with a broom magnet, and a 391.4 nm photometer were flown. The data from this flight indicate that the energetic particle flux consists predominantly of protons, neutral hydrogen and possibly other energetic nuclei. The energy spectrum becomes much softer and the flux more intense with increasing Kp for 10<E<100 keV. The pitch angle distribution at 180 km is asymmetrical with a peak at 90° indicating that the majority of particles are near their mirroring altitude. Ionization rates are calculated based on the measured energy spectrum and mirror height distribution. The resulting ionization rate profile is found to be nearly constant with altitude in the region 120 to 200 km. The measured energetic particle flux and calculated ionization rate from the five flights are found to vary with magnetic activity (based on the Kp and Dst indexes) in the same way as the independently derived ionization rates deduced from the electron density profile.

Laser heating and ionization of magnetically confined plasmas in the presence of strong uv and x radiation

A simple one-dimensional model has been developed to describe the propagation of laser radiation into an underdense magnetically confined moderate-Z plasma. A time-dependent Coronal atomic physics code is used to calculate ionization rates and radiative losses. Radiation losses during the ionization process dominate the energy balance and set an intensity-dependent threshold laser fluence for stripping ions such as neon down to a He-like configuration. Attainment of the He-like configuration is marked by a very large reduction in the soft radiation rate plus a sharp increase in the plasma temperature and laser absorption length. This is manifested by the onset of an exponentially increasing K-shell x-radiation rate which has been observed in a small laser-heated neon theta pinch.

Derivation of ionization equations for the simulation of auroral effects

Equations are derived for calculating ionization rates for three basic types of electron energy spectrum distributions. These can be combined to model observed auroral electron energy distributions, in order to simulate auroral effects and effects due to electron precipitation, Calculated auroral 5577 A0/3914 A0 intensity ratios, using the ionization rates obtained by means of the derived equations, at the altitudes of 120, 160 and 200 km, show good agreement with observations.

Atmospheric helium and geomagnetic field reversals

The problem of the earth's helium budget is examined in the light of recent work on the interaction of the solar wind with nonmagnetic planets. It is proposed that the dominant mode of helium (4He) loss is ion pumping by the solar wind during geomagnetic field reversals, when the earth's magnetic field is very small. The interaction of the solar wind with the earth's upper atmosphere during such a period is found to involve the formation of a bow shock. The penetration altitude of the shock-heated solar plasma is calculated to be about 700 km, and ionization rates above this level are estimated for a cascade ionization (electron avalanche) process to average 109 ions cm−2 sec−1. The calculated ionization rates and the capacity of the solar wind to remove ionized helium (4He) from the upper atmosphere during geomagnetic dipole reversals are sufficient to yield a secular equilibrium over geologic time scales. The upward transport of helium from the lower atmosphere under these conditions is found to be adequate to sustain the proposed loss rate. The implications of the differential ion pumping for other constituents are outlined for the earth's atmosphere. A pumping rate for Venus is inferred, which is sufficient to remove the hydrogen associated with about 30 atm of water from the upper Cytherian atmosphere during geologic time. The terrestrial ³He budget is strongly affected both by this mechanism and by enhanced production by cosmic rays during the depression of the geomagnetic field before and after a reversal.

The effect of errors in rate constants on non-equilibrium shock layer electron density calculations

In a study of non-equilibrum ionization in shock layers, the chemical system (1) O 2 + X ⇌ O + O + X (2) O + N 2 ⇌ N + NO (3) O + NO ⇌ N + O 2 (4) N + O ⇌ NO + + e was adopted as the simplest system which could reasonably be used in calculation of ionization rates and times. Use of the rates of the individual reactions permitted the calculations of the electron density and other concentrations in the plasma sheath as functions of time. Important quantities in such calculations are the reaction rate constants which, together with the concentrations, determine the actual rates. Values of these constants are greatly in doubt. A programme was set up to determine the effect of inaccuracies in these values. Each pair of rate constants was changed individually and the effect on each concentration-time curve was noted. Large effects were found. In one typical case, a change of one order of magnitude in the rate constant of the O 2 dissociation changed the electron density after about two msec by a factor of about 200. Changes of other rate constants by an order of magnitude changed the overall rate of ionization by lesser, but still serious, factors. It is therefore concluded that non-equilibrium electron density calculations are extremely dependent on the values of the rate constants and precise values are needed.

Ionization Times of Impurities in Hydrogen Plasmas

The problem discussed is the calculation of the time it takes for impurity atoms and ions to become ionized in the hydrogen plasma produced in pulsed thermonuclear machines. Classical ionization cross sections are used to calculate ionization rates and the effect of radiative recombination is included. The importance of taking into account the time dependence of the state of ionization is illustrated by an example where the energy radiated by an impurity of carbon is estimated. The time for impurity ions to reach the steady state is compared with the duration of the discharge for a number of operating thermonuclear machines and it is found that the latter times are too short for the steady state to be established. The assumption of the steady state is shown to be acceptable for a power producing D-D reactor.

Theory of Electron Multiplication in Silicon and Germanium

Using methods similar to those employed to treat the gas discharge, a theory is developed to explain the multiplication of electrons (and holes) in Si and Ge junctions. The calculations take into account the effects of electron-phonon and pair-producing collisions on the distribution function. In Si, the only element for which complete measurements have been made, the calculated ionization rate versus field curve is in agreement with experiment if one assumes a mean free path of 200A for interactions between electrons and optical phonons.

Probe Studies of Energy Distributions and Radial Potential Variations in a Low Pressure Mercury Arc

Probe measurements were made in the plasma of a low pressure mercury arc. The electron-energy distributions showed depletions from a Maxwellian distribution in the high energy range. Coupling effects between adjacent probes were investigated and were found to be quite small but in the proper direction to agree with the Langmuir-Tonks theory. Drift-current distortion of the random electron-energy distributions was measured with a bidirectional probe and compared with theory. A multisection probe extending from tube axis to tube wall allowed a determination of radial potential and density variations. Results over a pressure range from 3.4 microns to 35 microns showed good agreement with the ambipolar diffusion theory based on cumulative ionization. A direct calculation of ionization rate in the plasma was made from the ionization probability for a one-step ionizing process; comparison of this calculation with the observed ionization rate at 1.7 microns indicated that at that pressure the ionization is half direct, half cumulative. For higher arc pressures cumulative ionization evidently predominates.