Total Ion Population Research Articles

On the ionospheric source region of cold ion outflow

Recent studies have shown that low energy ions constitute a significant part of the total ion population in the Earth's magnetosphere. In this study, we have used a comprehensive data set with measurements of cold (total energy less than 70 eV) ion velocity and density to determine their source. This data set is derived from Cluster satellite measurements combined with solar wind and interplanetary magnetic field measurements and geomagnetic indices. By using the guiding center equation of motion, we were able to calculate the trajectories and thus determine the source region of the cold ions. Our results show that the polar cap region is the primary source for cold ions. We also found that the expansion and contraction of the polar cap as a consequence of changes in solar wind parameters were correlated with the source region size and intensity of the cold ion outflow. Elevated outflow fluxes near the nightside auroral zone and the dayside cusps during disturbed conditions suggest that energy and particle precipitation from the magnetosphere or directly from the solar wind can enhance the outflow of cold ions from the ionosphere.

How to write a paper for Rapid Communications in Mass Spectrometry

How to write a paper for <i>Rapid Communications in Mass Spectrometry</i>

Calibration Function for the Orbitrap FTMS Accounting for the Space Charge Effect

Ion storage in an electrostatic trap has been implemented with the introduction of the Orbitrap Fourier transform mass spectrometer (FTMS), which demonstrates performance similar to high-field ion cyclotron resonance MS. High mass spectral characteristics resulted in rapid acceptance of the Orbitrap FTMS for Life Sciences applications. The basics of Orbitrap operation are well documented; however, like in any ion trap MS technology, its performance is limited by interactions between the ion clouds. These interactions result in ion cloud couplings, systematic errors in measured masses, interference between ion clouds of different size yet with close m/z ratios, etc. In this work, we have characterized the space-charge effect on the measured frequency for the Orbitrap FTMS, looking for the possibility to achieve sub-ppm levels of mass measurement accuracy (MMA) for peptides in a wide range of total ion population. As a result of this characterization, we proposed an m/z calibration law for the Orbitrap FTMS that accounts for the total ion population present in the trap during a data acquisition event. Using this law, we were able to achieve a zero-space charge MMA limit of 80 ppb for the commercial Orbitrap FTMS system and sub-ppm level of MMA over a wide range of total ion populations with the automatic gain control values varying from 10 to 10(7).

Utilizing Artificial Neural Networks in MATLAB to Achieve Parts-Per-Billion Mass Measurement Accuracy with a Fourier Transform Ion Cyclotron Resonance Mass Spectrometer

Fourier transform ion cyclotron resonance mass spectrometry has the ability to realize exceptional mass measurement accuracy (MMA); MMA is one of the most significant attributes of mass spectrometric measurements as it affords extraordinary molecular specificity. However, due to space-charge effects, the achievable MMA significantly depends on the total number of ions trapped in the ICR cell for a particular measurement, as well as relative ion abundance of a given species. Artificial neural network calibration in conjunction with automatic gain control (AGC) is utilized in these experiments to formally account for the differences in total ion population in the ICR cell between the external calibration spectra and experimental spectra. In addition, artificial neural network calibration is used to account for both differences in total ion population in the ICR cell as well as relative ion abundance of a given species, which also affords mean MMA values at the parts-per-billion level.

Observations of molecular oxygen ions in Saturn's inner magnetosphere

We present an analysis of molecular oxygen ion (O2+) abundance in Saturn's inner magnetosphere based on observations made with the Cassini Plasma Spectrometer (CAPS). Using data summed over 23 orbits, we resolve and isolate O2+ counts from the tail of the water group ion mass distribution (W+ [O+, OH+, H2O+, H3O+]) and from background sources. O2+ was initially estimated at ∼1–2% of the total ion population in the inner magnetosphere based on CAPS data from the Saturn orbital insertion pass. Through refined analysis techniques, we have found O2+ to account for just above 0.3% of all W+ ions at L = 4.5, with only minor fluctuations in relative density out to L = 7.5 − 8.0. Beyond L = 7.5, the relative O2+/W+ abundance exhibits a statistically significant increase through L = 10.5, which may indicate a neutral O2 source in the vicinity of Rhea.

Parts-per-billion mass measurement accuracy achieved through the combination of multiple linear regression and automatic gain control in a Fourier transform ion cyclotron resonance mass spectrometer.

Fourier transform ion cyclotron resonance mass spectrometry has the ability to achieve unprecedented mass measurement accuracy (MMA); MMA is one of the most significant attributes of mass spectrometric measurements as it affords extraordinary molecular specificity. However, due to space-charge effects, the achievable MMA significantly depends on the total number of ions trapped in the ion cyclotron resonance (ICR) cell for a particular measurement. Even through the use of automatic gain control (AGC), the total ion population is not constant between spectra. Multiple linear regression calibration in conjunction with AGC is utilized in these experiments to formally account for the differences in total ion population in the ICR cell between the external calibration spectra and experimental spectra. This ability allows for the extension of dynamic range of the instrument and for the mean MMA values to remain less than 1 part-per-million (ppm). In addition, multiple linear regression calibration is used to account for both differences in total ion population in the ICR cell as well as relative ion abundance of a given species, which also affords mean MMA values at the parts-per-billion (ppb) level.

Auroral ion composition during large magnetic storms

Ion-composition measurements from the suprathermal mass spectrometer (SMS) on AKEBONO (EXOS-D) during large magnetic storms (minimum Dst &lt; −50 nT) reveal substantial changes in the mass composition of the auroral ionosphere. At quiet times, H+ and O+ ions dominate the high-altitude (&gt; 1000 km) polar (Λ &gt; 70°) ionosphere, and the minor-ion species (He+, N+, and O++) typically constitute about 10% of the total ion population: N+/O+ ≈ 0.05–0.1 and O++/O+ ≈ 0.1–0.2. During magnetic storms, the relative abundance of minor ions increase substantially, and N+ becomes a significant, at times dominant, component. During the main phase of large storms, the N+/O+ ratio reaches peak values of unity in the dayside. Likewise, the peak O++/O+ ratio reaches 0.4–0.5 at storm time. In addition, molecular [Formula: see text] and NO+ ions are occasionally present, and constitute ~5% of the total ion flux. The observed ions typically have energies of 5–20 eV/q, and are moving upward along the field line. They are believed to originate from the topside ionosphere. The increased abundance of N+ ions during large magnetic storms is believed to be a direct result of the increase in molecular nitrogen density in the F-region and topside ionosphere due to thermospheric heating in the presence of prolonged auroral activity. This implies that N+ ions may possibly be the dominant plasma component in the magnetosphere during very large magnetic storms.

Some features of RF excited fully ionized low pressure argon plasma

Using less than 1 kW of rf (≈10 MHz) power resonantly coupled into a 5 cm diameter, 40 cm long argon magnetoplasma, electron densities greater than 10 13 cm −3 and energies of about 3 eV have been achieved at pressures of a few mTorr. The discharge appears to be in coronal equilibrium at low pressures with up to half the total ion population estimated to be doubly ionized.

Multiple equilibria and poloidal rotation instabilities in tokamak plasmas

In tokamak plasma with substantial impurity (nzZ2≫ni), convective inertia effects lead to strong nonuniformity of both nz and the electrostatic potential on a magnetic surface. These effects make the response of the total ion population to poloidal rotation (V̄ϑ) highly nonlinear, introducing the possibility of multiple equilibria. The equations are applied to the central sawtooth region of the plasma where the gradients nj′, Tj′ are small. Above a critical electron temperature (Tc1) the equilibrium with low V̄ϑ is lost, leading to an m = 0, n = 0 poloidal rotation instability. The properties of this mode match the sawtooth disruptions and Tc1 accurately predicts the central electron temperature. The cause of sawtooth disruptions in low impurity plasmas is discussed.

A quantitative examination of the LTE condition in the effluent of an atmospheric pressure argon plasma jet

A sensitive and relatively unambiguous experimental test for local thermodynamic equilibrium (LTE) has been carried out 3 mm from the orifice of an unconfined atmospheric-pressure argon plasma jet with a front electrode L/D ratio of about 3. It was assumed only that the plasma consisted of the four species, argon atoms, metastable argon atoms, electrons, and argon ions, in intimate mixture. The Kramers-Unsöld relation normalized by in situ use of an Olsen arc (a device taken to be in thermodynamic equilibrium) was used to determined from the continuum radiance coefficient the pointwise electron and hence argon ion concentration. The concentration of 19·22 eV excited argon ions was determined by absolute intensity measurement of the 4806·90 Å line. The ratio of the concentration of these excited emitters to the measured total ion population was used in the appropriate Boltzmann equation to obtain a unique and sensitively determined ion-excitation temperature parameter, T α. To demonstrate LTE, it remains only to show that the absolute populations of argon ions and of metastables, calculated by the well-known principles of statistical mechanics for temperature T α, are in agreement with those observed. Ion populations were determined as described above, and metastable populations inferred from those for the 1·78 eV excited metastable state which gives rise to the 6965·43 Å line. Finally, the ion excitation temperature profile was extrapolated in a reasonable way to the edge of the jet, and the theoretical heat flow was computed for a proportional velocity profile. Satisfactory agreement with measured heat flux was obtained.