Ion-ion Recombination Rate Research Articles

Pressurized rf cavities in ionizing beams

A muon collider or Higgs factory requires significant reduction of the six dimensional emittance of the beam prior to acceleration. One method to accomplish this involves building a cooling channel using high pressure gas filled radio frequency cavities. The performance of such a cavity when subjected to an intense particle beam must be investigated before this technology can be validated. To this end, a high pressure gas filled radio frequency (rf) test cell was built and placed in a 400 MeV beam line from the Fermilab linac to study the plasma evolution and its effect on the cavity. Hydrogen, deuterium, helium and nitrogen gases were studied. Additionally, sulfur hexafluoride and dry air were used as dopants to aid in the removal of plasma electrons. Measurements were made using a variety of beam intensities, gas pressures, dopant concentrations, and cavity rf electric fields, both with and without a 3 T external solenoidal magnetic field. Energy dissipation per electron-ion pair, electron-ion recombination rates, ion-ion recombination rates, and electron attachment times to $SF_6$ and $O_2$ were measured.

Investigation of ion–ion-recombination at atmospheric pressure with a pulsed electron gun

For future development of simple miniaturized sensors based on pulsed atmospheric pressure ionization as known from ion mobility spectrometry, we investigated the reaction kinetics of ion-ion-recombination to establish selective ion suppression as an easy to apply separation technique for otherwise non-selective ion detectors. Therefore, the recombination rates of different positive ion species, such as protonated water clusters H(+)(H(2)O)(n) (positive reactant ions), acetone, ammonia and dimethyl-methylphosphonate ions, all recombining with negative oxygen clusters O(2)(-)(H(2)O)(n) (negative reactant ions) in a field-free reaction region, are measured and compared. For all experiments, we use a drift tube ion mobility spectrometer equipped with a non-radioactive electron gun for pulsed atmospheric pressure ionization of the analytes. Both, ionization and recombination times are controlled by the duty cycle and repetition rate of the electron emission from the electron gun. Thus, it is possible to investigate the ion loss caused by ion-ion-recombination depending on the recombination time defined as the time delay between the end of the electron emission and the ion injection into the drift tube. Furthermore, the effect of the initial total ion density in the reaction region on the ion-ion-recombination rate is investigated by varying the density of the emitted electrons.

Charged and total particle formation and growth rates during EUCAARI 2007 campaign in Hyytiälä

Abstract. Despite the fact that frequent aerosol formation has been observed in various locations in the atmosphere, the overall magnitude of the new particle formation as a particle source is still unclear. In order to understand the particle formation and growth processes, we investigate the magnitudes of the particle formation and growth rates at the size where the real atmospheric nucleation and activation occurs. The relative contribution of neutral and charged particles to the new particle formation rate is also studied. The data include particle and ion number size distributions and total particle concentration measurements at a boreal forest site in Hyytiälä, Finland, during the spring 2007 EUCAARI field campaign. The total and charged particle formation rates differed from each other by approximately an order of magnitude. The median formation rates of 2 nm total and charged particles were 0.65 cm−3 s−1 and 0.03 cm−3 s−1, respectively. The median growth rates of particles in size classes 1.3–3, 3–7 and 7–20 nm were 1.9, 3.6 and 4.2 nm h−1, respectively. The calculated ion-ion recombination rates were about the same order of magnitude as the ion-induced formation rates. The results indicate that the ion-induced nucleation involving the ion-ion recombination products, i.e. ion mediated nucleation, contributes approximately 10% to the boreal forest new particle formation events.

Numerical predictions of aerosol charging and electrical conductivity of the lower atmosphere of Mars

The charging of aerosols and the conductivity of the lower, night time atmosphere of Mars are calculated. The charge distribution of aerosols was obtained by the simultaneous solution of the ion‐aerosol charge balance equations. Galactic cosmic rays are the dominant ionizing process in the night time lower atmosphere producing molecular ions and ion clusters. The ion production rates for different solar activities are considered. The ion‐ion recombination rates and the ion‐aerosols attachment coefficients are calculated for altitudes from 0 to 70 km. Both the steady state and time dependent concentration of charged aerosols are calculated. The conductivity produced by ion‐attachment of aerosols was found to decrease by a factor of five yielding a value of about 4 × 10−12 Ohm−1 m−1 close to the surface. The effect on the conductivity of the temperature vs. altitude and the aerosol density are also estimated.

Electron and negative ion densities in C2F6 and CHF3 containing inductively coupled discharges

Electron and negative ion densities have been measured in inductively coupled discharges containing C2F6 and CHF3. Line integrated electron density was determined using a microwave interferometer, negative ion densities were inferred using laser photodetachment spectroscopy, and electron temperature was determined using a Langmuir probe. For the range of induction powers, pressures and bias power investigated, the electron density peaked at 9×1012 cm−2 (line-integrated) or approximately 9×1011 cm−3. The negative ion density peaked at approximately 1.3×1011 cm−3. A maximum in the negative ion density as a function of induction coil power was observed. The maximum is attributed to a power dependent change in the density of one or more of the potential negative ion precursor species since the electron temperature did not depend strongly on power. The variation of photodetachment with laser wavelength indicated that the dominant negative ion was F−. Measurement of the decay of the negative ion density in the afterglow of a pulse modulated discharge was used to determine the ion–ion recombination rate for CF4, C2F6, and CHF3 discharges.

Behavior of Electrons and Negative Ions in a Capacitively-Coupled Radio-Frequency NF 3/Ar Plasma

The behaviors of electrons and negative ions in a low-pressure (100 mTorr) capacitively-coupled radio-frequency (13.56 MHz) NF3/Ar plasma have been studied at a low-power level (2–10 W) using a laser photodetachment technique combined with a microwave cavity resonance method for determining electron density. The wavelength dependent photodetachment measurement indicated that F- is the predominant negative ion species in the plasma. The negative ion density was higher than the electron density by a factor of ∼50 at a NF3 mixing ratio r as low as 1% and the negative-ion/electron density ratio further increased with increasing r mainly because of the decrease in the electron density. The overall change in the negative ion density in the studied range of 1%<r<40% was relatively small (a factor of ∼2). For small r (<∼10%), the negative ion density increased with decreasing r; the change in the electron-attachment and ion-ion recombination rate constants with varying r was investigated to explain the phenomenon.

Ion-ion recombination in a gas discharge.

We present results of a Monte Carlo simulation of the recombination of positive methane ions and negative sulfur hexafluoride ions in an electric discharge at atmospheric pressure. The results of the simulation are directly compared with recent experimental measurements of the ion-ion recombination rate in discharges through gas mixtures of methane and sulfur hexafluoride.

Ion aging effects on the dissociative-attachment instability in CO2 lasers

Onset of the dissociative-attachment instability requires that the rate coefficient for electron detachment (kd) from negative ions be below a critical value. The predominant negative and positive ions in a CO2∶N2∶He gas-discharge plasma are known to change with time. As secondary by-products form and the predominant negative-ion species changes from CO3− to NO2−, a decrease inkd occurs destabilizing the discharge. Since NO2− and NO3− are largely unreactive with respect to associative detachment,kd depends in a sensitive fashion on the concentration of certain minority negative ions (O−, O2−) and neutrals (CO, O, N). The sufficient conditions for the dissociative-attachment instability are much less sensitive to changes in the electron-ion and ion-ion recombination rate coefficients resulting from the ion aging process.

Plasma Shielding Effects on Ionic Recombination

Monte Carlo calculations are presented of the ion-ion recombination rate coefficient for the ${\mathrm{Kr}}^{+}$ + ${\mathrm{F}}^{\ensuremath{-}}$ + Ar reaction. The effect of other ions on the recombination rate is taken into account by use of the Debye screened potential rather than the Coulomb potential. This potential should be valid for ion densities between ${10}^{13}$ and ${10}^{15}$ ${\mathrm{cm}}^{\ensuremath{-}3}$. Results are presented for ion densities in this range and for neutral pressures of 0.5 to 8.0 atm. It is found that screening effects significantly decrease the ion-ion recombination rate.

Calculations of ion-ion recombination rates at high pressures

The classical theory of ion-ion recombination in gases of high density is extended to allow for arbitrary ratios of the masses of the three species involved. Calculations are performed for the recombination of Ar+, Ar+2, Kr+, and Kr+2 ions with F− and of Hg+ and Ar+ with Cl− in an argon gas. The effective two-body rates peak between 2×10−6 and 3×10−6 cm3 sec−1 at pressures above 1 atm.

Ion-ion recombination rates in the earth's atmosphere

The temperature dependence of the binary recombination coefficient, α 2, for the reaction NO ++NO 2 − → products has been obtained over the range 185–530 K. It is found that the corresponding mean cross section σ is described by the power law σ ≅ A · T −0.9 , and that α 2 ≅ B · T −0.4. Data has also been obtained for two cluster ion recombination reactions which indicate that their recombination cross sections are only about 40% larger than for the parent ions at a given temperature, the cross sections for these reactions also apparently increasing with decreasing temperature. In the light of this data and by considering the most probable positive and negative ions existing at various altitudes up to 90km in the atmosphere, the most appropriate ionic recombination coefficients in various altitude ranges are deduced. Thus, between 30 and 90 km, where the recombination process is two-body, the coefficient varies over the narrow range 5–9 × 10 −8 cm 3s −1, while below 30 km the process is predominantly three-body with an effective two-body rate increasing rapidly to a maximum value ≈3 × 10 −6 cm 3s −1 in the troposphere, these deductions being based on published laboratory determinations of three-body recombination coefficients.

Ion-Ion Recombination in Laboratory Air

The ion-ion recombination rate in laboratory air at atmospheric pressure and room temperature has been re-investigated experimentally. Both pulsed and continuous irradiation methods were used. The pulsed source enabled the recombination coefficient to be measured as a function of ion age between ½ msec and ½ sec. It has been shown that the very high initial recombination rates at low ion ages can be satisfactorily explained by the existence of microscopic regions in which the ion density is much higher than the average density over the ionized volume. Decreases in the recombination coefficient which were observed in a few cases at about 50 msec ion age have been attributed to changes in the type of ions involved. Day-to-day variations in the recombination coefficient were ascribed to variations in the minor constituents of the air used. The results of pulsed and continuous methods for recombination coefficient are in quantitative agreement yielding a value of 1·4×10−6 cm3 sec−1 for untreated laboratory air. Although the air used was not necessarily representative of other laboratory environments, this value shows that for much practical work a recombination coefficient considerably lower than that reported in the literature for carefully dried air should be used.