Total Number Of Ions Research Articles

Intense laser driven collision-less shock and ion acceleration in magnetized plasmas

The generation of strong magnetic field with a laser driven coil has been demonstrated by many experiments. It is applicable to the magnetized fast ignition (MFI), the collision-less shock in the astrophysics and the ion shock acceleration. In this paper, the longitudinal magnetic field effect on the shock wave driven by the radiation pressure of an intense short pulse laser is investigated by theory and simulations. The transition of a laminar shock (electro static shock) to the turbulent shock (electromagnetic shock) occurs, when the external magnetic field is applied in near relativistic cut-off density plasmas. This transition leads to the enhancement of conversion of the laser energy into high energy ions. The enhancement of the conversion efficiency is important for the ion driven fast ignition and the laser driven neutron source. It is found that the total number of ions reflected by the shock increases by six time when the magnetic field is applied.

Markov State Model of Ion Assembling Process.

We study the process of ion assembling in aqueous solution by means of molecular dynamics. In this article, we present a method to study many-particle assembly using the Markov state model formalism. We observed that at NaCl concentration higher than 1.49 mol/kg, the system tends to form a big ionic cluster composed of roughly 70-90% of the total number of ions. Using Markov state models, we estimated the average time needed for the system to make a transition from discorded state to a state with big ionic cluster. Our results suggest that the characteristic time to form an ionic cluster is a negative exponential function of the salt concentration. Moreover, we defined and analyzed three different kinetic states of a single ion particle. These states correspond to a different particle location during nucleation process.

Dependence of silicon ablation regimes on fluence during ultrafast laser irradiation

AbstractModels and experiments were developed to study femtosecond laser ablation of silicon using 800 nm, 40 fs pulses with fluences ranging from 0.5 to 35 J/cm2. At low fluences, ablation was found to occur due to bubble formation and splashing within the melt layer. At higher fluences, it was found that the ablation depth exceeded the melt layer depth due to shockwave ablation. The variation in ion flux and ion velocity was also studied both experimentally and theoretically. It was found that the variation in ion flux is mainly dependent on the variation in the average charge state, with only a small variation in the total number of ions above $\sim \!\!1.5\; \,{\rm J/c}{{\rm m}^2}$. Comparisons between the theoretical and experimental ion flux showed that higher charge state ions received greater portion of the laser energy compared with lower charge state ions.

Computational model of the interaction of a helium atmospheric-pressure jet with a dielectric surface

Using a time-dependent two-dimensional axisymmetric fluid model the interaction of a plasma jet with a dielectric surface has been studied. The model is solved for two consecutive periods of a positive unipolar pulsed waveform. The study concentrates on determining the fluxes of the main oxygen ion species, , and the total accumulated charge on the surface. Approaching the dielectric surface, the streamer head is seen to divert its direction of propagation, spreading out radially approximately 0.2 mm above the dielectric surface. For generated near the streamer head, this leads to a maximum in their flux to the surface which moves radially outwards with the streamer propagation, driven by the applied electric field in pulse on-time. In the off-time, the flux of drops by at least two orders of magnitude. As a result, the total number of ions arriving at the surface over one entire pulse period (fluence) has an annular shape limited by the effective contact area of the streamer on the surface. In contrast ions generated in the pulse on-time do not reach the surface due to the direction of the applied electric field. In the off-time, ions generated at the edges of the deformed streamer are pushed by the accumulated surface charge outwards. As a result, the fluence has an annular structure with its maximum being outside the area of the dielectric surface covered by the plasma channel. Solving for the second pulse period shows small changes in the predicted fluences, with largest difference seen with . We see that increasing the flow rate (by a factor of three) shifts the position of the maximum fluence of outwards, and decreasing the fluence in the second pulse period.

ChemInform Abstract: Formation of Gas‐Phase Peptide Ions and Their Dissociation in MALDI: Insights from Kinetic and Ion Yield Studies

AbstractReview: 130 refs.

Mass spectrometric and charge density studies of organometallic clusters photoionized by gigawatt laser pulses.

Clusters on exposure to nanosecond laser pulses of gigawatt intensity exhibit a variety of photo-chemical processes such as fragmentation, intracluster reaction, ionization, Coulomb explosion, etc. Present article summarizes the experimental results obtained in our laboratory utilizing time-of-flight mass spectrometer which deal with one such aspect of cluster photochemistry related to generation of multiply charged atomic ions upon excessive ionization of cluster constituents (Coulomb explosion) at low intensity laser field (∼109 W/cm2 ). To understand the mechanism of laser-cluster interaction, laser as well as cluster parameters were varied. Mass spectrometric studies were carried out at different laser wavelength as well as varying the nature of cluster constituents, backup pressure, nozzle diameter, etc. In addition, charge density measurements were also preformed to get information about the total number of ions generated upon laser-cluster interaction as a function of laser wavelength. In case of pure molecular clusters, the charge state of atomic ions as well as charge density was observed to enhance with increasing laser wavelength, signifying efficient coupling of the cluster medium with nanosecond laser pulse at longer wavelength. While in case of clusters doped with species having comparatively lower ionization energy, the efficiency of laser-cluster interaction was less, in contrast to studies carried out using femtosecond lasers. Results obtained in the present work have been rationalized on the basis of proposed three-stage cluster ionization mechanism, that is, multiphoton ionization ignited-inverse Bremsstrahlung heating and electron ionization. © 2015 Wiley Periodicals, Inc. Mass Spec Rev. 36:188-212, 2017.

Angular distribution of energetic argon ions emitted by a 90 kJ Filippov-type plasma focus

Characteristics of the energetic argon ions emitted by a 90 kJ Filippov-type plasma focus are studied by employing an array of Faraday cups. The Faraday cups are designed to minimize the secondary electron emission effects on their response. Angular distribution of the ions is measured, and the results indicate a highly anisotropic emission with a dip at the device axis and a local maximum at the angle of 7° with respect to the axis. It has been argued that this kind of anisotropic emission may be related to the surfatron acceleration mechanism and shown that this behavior is independent of the working gas pressure. It has been also demonstrated that this mechanism is responsible for the generation of MeV ions. Measuring the total ion number at different working gas pressures gives an optimum pressure of 0.3 Torr. In addition, the energy spectrum of ions is measured by taking into account of the ambient gas effects on the energy and charge of the ions. The current neutralization effect of electrons trapped in the ion beam as well as the effect of conducting boundaries surrounding the beam, on the detected signals are investigated.

Ionization balance in Titan’s nightside ionosphere

Based on a multi-instrumental Cassini dataset we make model versus observation comparisons of plasma number densities, nP=(nenI)1/2 (ne and nI being the electron number density and total positive ion number density, respectively) and short-lived ion number densities (N+, CH2+, CH3+, CH4+) in the southern hemisphere of Titan’s nightside ionosphere over altitudes ranging from 1100 and 1200km and from 1100 to 1350km, respectively. The nP model assumes photochemical equilibrium, ion–electron pair production driven by magnetospheric electron precipitation and dissociative recombination as the principal plasma neutralization process. The model to derive short-lived-ion number densities assumes photochemical equilibrium for the short-lived ions, primary ion production by electron-impact ionization of N2 and CH4 and removal of the short-lived ions through reactions with CH4. It is shown that the models reasonably reproduce the observations, both with regards to nP and the number densities of the short-lived ions. This is contrasted by the difficulties in accurately reproducing ion and electron number densities in Titan’s sunlit ionosphere.

Field-Induced Spin-State Transition in LaCo1−xMxO3 (M = Al, Ga, Rh, and Ir)

We have investigated the high-field magnetization of lightly doped LaCo1−xMxO3 with M = Al, Ga, Rh, and Ir up to 67 T. The transition field for the field-induced spin-state transition at 4.2 K, which is μ0Hc = 60 T in LaCoO3, increases slightly for M = Al but does not change for M = Ga. On the other hand, the transition field decreases remarkably for M = Rh and Ir. The substitution effect on μ0Hc has been interpreted as arising from the lattice-volume dependence of the excitation energy ΔI of CoI from the low-spin (LS) to high-spin (HS) state. The fraction of CoI is 15% of the total number of Co ions. The remaining Co ions, CoII, are excited from the LS to intermediate-spin (IS) state and contribute to the magnetization at high temperatures above 100 K. We propose the coexistence of the HS and IS states in LaCo1−xMxO3. For M = Rh and Ir, Co species with the magnetic ground state, CoIII, are populated by their substitution. The formation mechanism and spin states of CoIII are discussed in comparison with those of the magnetic Co species in La1−xSrxCoO3.

Hybridizing ultraviolet photodissociation with electron transfer dissociation for intact protein characterization.

We report a hybrid fragmentation method involving electron transfer dissociation (ETD) combined with ultraviolet photodissociation (UVPD) at 193 nm for analysis of intact proteins in an Orbitrap mass spectrometer. Integrating the two fragmentation methods resulted in an increase in the number of identified c- and z-type ions observed when compared to UVPD or ETD alone, as well as generating a more balanced distribution of a/x, b/y, and c/z ion types. Additionally, the method was shown to decrease spectral congestion via fragmentation of multiple (charge-reduced) precursors. This hybrid activation method was facilitated by performing both ETD and UVPD within the higher energy collisional dissociation (HCD) cell of the Orbitrap mass spectrometer, which afforded an increase in the total number of fragment ions in comparison to the analogous MS3 format in which ETD and UVPD were undertaken in separate segments of the mass spectrometer. The feasibility of the hybrid method for characterization of proteins on a liquid chromatography timescale characterization was demonstrated for intact ribosomal proteins.

Quantum corrections to nonlinear ion acoustic wave with Landau damping

Quantum corrections to nonlinear ion acoustic wave with Landau damping have been computed using Wigner equation approach. The dynamical equation governing the time development of nonlinear ion acoustic wave with semiclassical quantum corrections is shown to have the form of higher KdV equation which has higher order nonlinear terms coming from quantum corrections, with the usual classical and quantum corrected Landau damping integral terms. The conservation of total number of ions is shown from the evolution equation. The decay rate of KdV solitary wave amplitude due to the presence of Landau damping terms has been calculated assuming the Landau damping parameter α1=me/mi to be of the same order of the quantum parameter Q=ℏ2/(24m2cs2L2). The amplitude is shown to decay very slowly with time as determined by the quantum factor Q.

A conservative discretization of the Poisson–Nernst–Planck equations on adaptive Cartesian grids

In this paper we present a novel hybrid finite-difference/finite-volume method for the numerical solution of the nonlinear Poisson–Nernst–Planck (PNP) equations on irregular domains. The method is described in two spatial dimensions but can be extended to three dimensional problems as well. The boundary of the irregular domain is represented implicitly via the zero level set of a signed distance function and quadtree data structures are used to systematically generate adaptive grids needed to accurately capture the electric double layer near the boundary. To handle the nonlinearity in the PNP equations efficiently, a semi-implicit time integration method is utilized. An important feature of our method is that total number of ions in the system is conserved by carefully imposing the boundary conditions, by utilizing a conservative discretization of the diffusive and, more importantly, the nonlinear migrative flux term. Several numerical experiments are conducted which illustrate that the presented method is first-order accurate in time and second-order accurate in space. Moreover, these tests explicitly indicate that the algorithm is also conservative. Finally we illustrate the applicability of our method in the study of the charging dynamics of porous supercapacitors.

Formation of gas-phase peptide ions and their dissociation in MALDI: insights from kinetic and ion yield studies.

Insights on mechanisms for the generation of gas-phase peptide ions and their dissociation in matrix-assisted laser desorption ionization (MALDI) gained from the kinetic and ion yield studies are presented. Even though the time-resolved photodissociation technique was initially used to determine the dissociation kinetics of peptide ions and their effective temperature, it was replaced by a simpler method utilizing dissociation yields from in-source decay (ISD) and post-source decay (PSD). The ion yields for a matrix and a peptide were measured by repeatedly irradiating a region on a sample and collecting ion signals until the sample in the region was completely depleted. Matrix- and peptide-derived gas-phase cations were found to be generated by pre-formed ion emission or by ion-pair emission followed by anion loss, but not by laser-induced ionization. The total number of ions, that is, matrix plus peptide, was found to be equal to the number of ions emitted from a pure matrix. A matrix plume was found to cool as it expanded, from around 800-1,000 K to 400-500 K. Dissociation of peptide ions along b/y channels was found to occur statistically, that is, following RRKM behavior. Small critical energy (E0 = 0.6-0.7 eV) and highly negative critical entropy (ΔS(‡) = -30 to -25 eu) suggested that the transition structure was stabilized by multiple intramolecular interactions.

Externally excited planar dust acoustic shock waves in a strongly coupled dusty plasma under microgravity conditions

The formation and dissipation of an externally excited planar dust acoustic shock wave in a three-dimensional uniform dust cloud has been observed under microgravity conditions. The experiment has been performed in the dc gas discharge chamber ‘Plasma Kristall-4’ (Fortov et al 2005 Plasma Phys. Control. Fusion 47 B537) on board the A300 Zero-G airplane. The shock Mach number and compression factor reached 3.5 and 6, correspondingly, with a shock width of about the interparticle distance. Due to the utilization of the polarity-switching dc discharge mode and application of the Rankine–Hugoniot relations, the dust particle electrostatic pressure was determined and the Hugoniot percussive adiabat for the dust subsystem was derived. The obtained data were simulated using thermodynamic properties of highly nonideal Debye–Hückel (Yukawa) systems. Comparison of the experimental and simulated data has demonstrated that the screening length in a dense dusty plasma is not determined by the total ion number density, but rather by those ‘effective’ ions which are not bounded by negatively charged dust grains. Thus, this work presents a new experimental approach for the investigation of the dense dusty plasma clouds.

Thermal Conductivity of Molten Alkali Metal Fluorides (LiF, NaF, KF) and Their Mixtures

The thermal conductivities of molten alkali fluorides (LiF, NaF, and KF) and their mixtures (LiF-NaF, LiF-KF, and NaF-KF binaries and LiF-NaF-KF ternary) are predicted using molecular dynamics simulation with the Green-Kubo method. A polarizable ion model is used to describe the interionic interactions. All the systems except LiF-KF and LiF-NaF-KF mixtures follow a scaling law: it is proportionnal to mA (-1/2)(N/V)(2/3), where mA is the arithmetic average of the ionic species masses in a given melt and N is the total number of ions included in the system volume V. In LiF-KF and LiF-NaF-KF mixtures a significant departure from the scaling law is observed. By examining separately the effects of the cation mass and size asymmetry in LiF-KF mixtures, we show that both of them account for half of the deviation. Finally, we observe that the temperature dependence of the thermal conductivity is very small in these molten fluorides.

Phase behavior of concentrated hydroxypropyl methylcellulose solution in the presence of mono and divalent salt

Thermo reversible sol–gel transitions of hydroxypropylmethylcellulose (HPMC) are critical for many pharmaceutical, cosmetic, and food applications. This study examined the effects of salt (NaCl and CaCl2) on the viscoelastic properties of concentrated low molecular weight HPMC solutions and found that the gelation temperature decreased linearly as a function of salt concentrations, independent of valency of cations and the mole concentration of anions. Thermal analysis showed that the depression of melting temperature can be fitted for both NaCl and CaCl2 as a function of the total number of ions by a single linear curve, which was consistent with the melting point depression of pure water by NaCl and CaCl2, but with a higher linear slope.

Influence of electron evaporative cooling on ultracold plasma expansion

The expansion of ultracold neutral plasmas (UCP) is driven primarily by the thermal pressure of the electron component and is therefore sensitive to the electron temperature. For typical UCP spatial extents, evaporative cooling has a significant influence on the UCP expansion rate at lower densities (less than 108/cm3). We studied the effect of electron evaporation in this density range. Owing to the low density, the effects of three-body recombination were negligible. We modeled the expansion by taking into account the change in electron temperature owing to evaporation as well as adiabatic expansion and found good agreement with our data. We also developed a simple model for initial evaporation over a range of ultracold plasma densities, sizes, and electron temperatures to determine over what parameter range electron evaporation is expected to have a significant effect. We also report on a signal calibration technique, which relates the signal at our detector to the total number of ions and electrons in the ultracold plasma.

Interpreting raw biological mass spectra using isotopic mass‐to‐charge ratio and envelope fingerprinting

Soft ionization, high-resolution mass spectrometry is widely used to characterize large biological molecules, such as proteins. Deconvolution ('deisotoping') of isotopic envelopes (iEs) in biological mass spectra into monoisotopic or average masses is challenging due to low signals and heavily overlapped iEs, resulting in many wrong interpretations. Isotopic envelopes (iEs) are directly used without deisotoping to identify biological molecules. An algorithm, isotopic mass-to-charge ratio (m/z) and envelope fingerprinting (iMEF), was implemented in the ProteinGoggle search engine for top-down intact protein database searching. iMEF combines isotopic m/z fingerprinting (iMF) and isotopic envelop fingerprinting (iEF), where 'Isotopic mass-to-charge ratio' means the m/z value of the most abundant isotopic peak within the iE of a precursor or product ion. iMF is used to 'fish' precursor or product ion candidates from the database, which is pre-built and contains all iE information (precursor and product ions) of all proteoforms of the studied system. iEF identifies matching precursor or product ions. A protein is finally identified with user-specified total number of matching product ions and post-translational modification scores. The working principles of iMEF and ProteinGoggle, and the definition of a set of related parameters and scoring metrics, are illustrated with high-resolution tandem mass spectrometric analysis of a mixture of ubiquitin and the HUMAN histone H4 proteoforms. Ubiquitin was confidently identified from its CID, ETD, and HCD spectra with 57, 91, and 66 matching product ions, respectively; 125 proteoforms were confidently found from the H4 dataset. The locations of PTMs in 54 and 6 isoforms were partially and fully identified. Database search with iMEF bypasses 'deisotoping' avoiding associated errors, and also provides full quality control of matching precursor and product ions and finally protein IDs. Overlapped iEs of different product ions could also be confidently unwrapped in situ. Improvement and addition of more functionalities and utilities of ProteinGoggle are underway.

Quantitative reproducibility of mass spectra in matrix‐assisted laser desorption ionization and unraveling of the mechanism for gas‐phase peptide ion formation

In a previous study on matrix-assisted laser desorption ionization (MALDI) of peptides using α-cyano-4-hydroxycinnamic acid (CHCA) as a matrix, we found that the patterns of single-shot spectra obtained under different experimental conditions became similar upon temperature selection. In this paper, we report that absolute ion abundances are also similar in temperature-selected MALDI spectra, even when laser fluence is varied. The result that has been obtained using CHCA and 2,5-dihydroxybenzoic acid as matrices is in disagreement with the hypothesis of laser-induced ionization of matrix as the mechanism for primary ion formation in MALDI. We also report that the total number of ions in such a spectrum is unaffected by the identity, concentration and number of analytes, i.e. it is the same as that in the spectrum of pure matrix. We propose that the generation of gas-phase ions in MALDI can be explained in terms of two thermal reactions, i.e. the autoprotolysis of matrix molecules and the matrix-to-analyte proton transfer, both of which are in quasi-equilibrium in the early matrix plume.

Kinetic analysis of the energy transport of bursty bulk flows in the plasma sheet

The energy transport of bursty bulk flows (BBFs) is very important to the understanding of substorm energy transport. Previous studies all use the MHD bulk parameters to calculate the energy flux density of BBFs. In this paper, we use the kinetic approach, i.e., ion velocity distribution function, to study the energy transport of an earthward bursty bulk flow observed by Cluster C1 on 30 July 2002. The earthward energy flux density calculated using kinetic approach QKx is obviously larger than that calculated using MHD bulk parameters QMHDx. The mean ratio QKx/QMHDx in the flow velocity range 200–800 km/s is 2.7, implying that the previous energy transport of BBF estimated using MHD approach is much underestimated. The underestimation results from the deviation of ion velocity distribution from ideal Maxwellian distribution. The energy transport of BBF is mainly provided by ions above 10 keV although their number density Nf is much smaller than the total ion number density N. The ratio QKx/QMHDx is basically proportional to the ratio N/Nf. The flow velocity v(E) increases with increasing energy. The ratio Nf/N is perfectly proportional to flow velocity Vx. A double ion component model is proposed to explain the above results. The increase of energy transport capability of BBF is important to understanding substorm energy transport. It is inferred that for a typical substorm, the ratio of the energy transport of BBF to the substorm energy consumption may increase from the previously estimated 5% to 34% or more.