Resonant Charge Exchange Research Articles

C− generation by charge exchange with non-metallic gas for positive ion mass spectrometry

Carbon positive ion mass spectrometry technology(C-PIMS) is a new type of mass spectrometry technology using the opposite charge exchange process of accelerator mass spectrometry (AMS). There is a plan at Peking University to build 14C-PIMS with the study of a compact 2.45 GHz ECR ion source for C2+ production and a charge exchange cell (CXC) for C2+ to C− conversion. In this paper, the profile of carbon ion source and CXC is introduced and the generation of C− ions is investigated. In experiment, five non-metallic gas targets are tested. 19 μA@90 keV C− beam is obtained from C2+ using the ethylene target. It is found that gas targets with low first ionization energy favor the generation of C−. In addition, the charge exchange efficiency at different beam energies (25 keV–90 keV) is investigated. In terms of theory, the mechanisms of resonant and non-resonant charge exchange processes are introduced to analyze the experimental results. Moreover, the charge exchange from C+ to C− is studied and the feasibility of C+-PIMS is discussed since 2.45 GHz ECR ion source produce more C+ ions. It is found that 139 μA@45 keV C− beam can be obtained from C+ using the methane target.

Studies of Dynamics of Neutral Component of Current Sheet Plasma, Based on Spectral Broadening of Helium Line He I 5876 Å

Spectroscopy methods were used for studying the dynamics of neutral plasma component in current sheets formed in two-dimensional (2D) and three-dimensional (3D) magnetic configurations during discharge in helium. It has been ascertained that when the current sheet is formed in the 2D magnetic field, flows of fast suprathermal helium atoms appear in it, which are directed along the current sheet width (the largest of the sheet transverse dimensions). It is shown that helium atoms can acquire the directed energy Wx due to the resonance charge exchange of accelerated ions in the current sheet plasma. The energy of directed motion of helium atoms can reach Wx ≈ (480 ± 120) eV, which is ~20 times higher than the temperature of helium atoms Ta ≈ (20 ± 2) eV at the same times. During the current sheet formation in the 3D magnetic configuration, fast helium atoms were not observed.

Azimuthal ion movement in HiPIMS plasmas—part I: velocity distribution function

Magnetron sputtering discharges feature complex magnetic field configurations to confine the electrons close to the cathode surface. This magnetic field configuration gives rise to a strong electron drift in azimuthal direction, with typical drift velocities on the order of 100 km s−1. In high power impulse magnetron sputtering plasmas, the ions have also been observed to follow the movement of electrons with velocities of a few km s−1, despite being not magnetized. In this work, we report on measurements of the azimuthal ion velocity using spatially resolved optical emission spectroscopy, allowing for a more direct measurement compared to experiments performed using mass spectrometry. The azimuthal ion velocities increase with target distance, peaking at about 1.55 km s−1 for argon ions and 1.25 km s−1 for titanium ions. Titanium neutrals are also found to follow the azimuthal ion movement which is explained with resonant charge exchange collisions. The experiments are then compared to a simple test-particle simulation of the titanium ion movement, yielding good agreement to the experiments when only considering the momentum transfer from electrons to ions via Coulomb collisions as the only source of acceleration in azimuthal direction. Based on these results, we propose this momentum transfer as the primary source for ion acceleration in azimuthal direction.

Theoretical study of resonant charge exchange between H−ion and adsorbate-covered metal surface Cu(111)/Cu(110) with adsorbates Li+/Na+

The influence of the surface type on resonant charge exchange between H−ion with a metal surfaces Cu(111) and Cu(110) covered by adsorbate Li+/Na+has been studied. A model static problem was considered. For modeling, athree-dimensional realization of the wave-packet propagation method was used. The Cu(110) andCu(111) surfaces were described by a pseudopotential, derived from a density functional theory (DFT).An occupation of H− ion, an electron density dynamics and an ion level width were analyzed. As aresult, we obtained that an electron oscillates more in case of the surface Cu(111). Furthermore, the resonant charge exchange is more efficient for Cu(111) surface.

Scattering cross sections and collision integrals for N(4S)–N+(3P) and N(4S)–N+(1D) interactions

Collisions between nitrogen (N) and nitrogen ion (N+) are fundamental phenomena in the Earth and planetary atmospheres. In this work, we carried out a theoretical study of collision data for N(4S)–N+(3P) and N(4S)–N+(1D) interactions, including scattering cross sections and collision integrals. Potential energy curves of N2+ are obtained using the state-of-the-art ab initio method and then used to provide the input for calculations of resonant charge exchange and elastic cross sections. The inelastic (corresponding to the resonant charge exchange process), elastic, and total collision integrals for N(4S)–N+(3P) and N(4S)–N+(1D) interactions are computed at 500 − 50 000 K. An analysis of the collision integrals shows that the elastic collision process should not be neglected for odd-order collision interactions at low temperatures and still makes a small contribution at high temperatures. Note that this is the first time that the cross sections and collision integrals for the N(4S)–N+(1D) interaction are calculated using ab initio potential energy points. The obtained cross sections and collision integrals are essential to model the transport properties of the related plasmas.

Collision integral of nitrogen and oxygen and application to artificially triggered lightning

The collision integrals for N, N+, N++, N2, O, O+, O++ and O2 were calculated by using the Sonine polynomial expansion based on Chapman theory. The calculations of collision integral have some dependent relationship on the electron temperature. Since resonant charge exchange exists between singly ionized ions and their parent neutral atoms, this requires a special consideration of inelastic collisions in calculating some neutral–ion interactions. Furthermore, the electron temperature, electron density and particle composition of the artificially triggered lightning were diagnosed. And the diffusion coefficient and electrical conductivity of the artificially triggered lightning were also determined.

Influence of single adsorbed atoms on charge exchange during ion-surface collisions

Partial and final projectile charge states are theoretically analyzed after ${\mathrm{Li}}^{+}$ ions frontally collide with a single-layer graphene surface with potassium atoms adsorbed on it, in the very low deposition limit where the adsorbed atoms negligibly interact with each other. We applied a model based on first principles that accounts for all the details of the surface and is used to describe the resonant charge exchange processes occurring in binary collisions between the projectile and the adsorbate, and between the projectile and the C atoms of the graphene surface located in the surroundings of the adsorption site. Completely different neutral fraction dependences with the outgoing velocity are found for the projectiles scattered by the adsorbate and by carbon atoms located far from the adsorbed atom. In addition, an important influence of the adsorbate is perceived in the neutralization of projectiles colliding with the first and second set of carbon atoms nearest to the adsorption site. For C atoms located at middle-range distances (\ensuremath{\sim}6.7 \AA{}), the final charge state of the projectile is not affected by the adsorbate presence, even when an effective interaction between the projectile and the K adsorbed atom is revealed via appreciable projectile level widths.

Monte Carlo model for ion mobility and diffusion for characteristic electric fields in nanodosimetry

The quantification of the effects of space radiation for manned spaceflight can be approximated by nanodosimetric measurements. For the development of nanodosimetric detectors, a Monte Carlo model for ion mobility and diffusion for characteristic electric fields is presented.This model can be used to describe the interactions of ions in their parent gas based solely on commonly known input parameters, such as the ionization potential, kinetic diameter, molar mass, and polarizability of the gas. A model for approximating the resonant charge exchange cross section has been proposed, requiring only the ionization energy and mass of the parent gas as input parameters. The method proposed in this work was tested against experimental drift velocity data for a wide range of gases (helium, neon, nitrogen, argon, krypton, carbon monoxide, carbon dioxide, oxygen, propane). The transverse diffusion coefficients were compared to experimental values for helium, nitrogen, neon, argon, and propane gas.With the Monte Carlo code and resonant charge exchange cross section approximation model presented in this work, it is now possible to calculate an estimate of the drift velocities, transverse diffusion, and thus the ion mobility of ions in their parent gas. This is essential for further nanodosimetric detector development, as those parameters are often not well known for the gas mixtures used in nanodosimetry.

Collision course; high-precision mass-independent and mass-dependent calcium isotope measurements using the prototype collision cell MC-ICPMS/MS, Proteus

This paper reports measurements of mass-independent and mass-dependent Ca isotope variations using the prototype collision cell MC-ICPMS/MS, Proteus. Helium and hydrogen gases are introduced into the collision cell and the well characterised resonant charge exchange and proton transfer reactions between Ar+ ions and H2 molecules results in almost complete removal of the 40Ar+ ions allowing the measurement of the 40Ca isotope by MC-ICPMS without resorting to ‘cold’ plasma.A range of reference materials have been characterised for both their mass-independent and mass-dependent Ca isotope compositions relative to the international reference material NIST SRM 915a. Notably, the radiogenic 40Ca/44Ca isotope ratio (internally normalised to 42Ca/44Ca) can be accurately measured with typical reproducibility better than 40 ppm (pooled 2 SD) for a single measurement using 12 μg of Ca. Reference materials USGS GSP‐2 and CRPG FKN have notably radiogenic 40Ca/44Ca, with values of 434 ± 7 and 5513 ± 17 ppm respectively relative to NIST SRM 915a (pooled 2 SE, n = 35 and 5 respectively). In contrast, multiple repeat measurements of mantle derived reference materials BIR, BHVO-2, BCR-2 and JP-1 yield values that are slightly unradiogenic (mean − 23 ± 5 ppm, pooled 2 SE, n = 71) relative to NIST SRM 915a, bone ash and seawater reference materials, likely reflecting crustal components in the latter. Coupled measurements of the minor 48Ca and 43Ca isotopes give 48Ca/44Ca and 43Ca/44Ca (internally normalised to 42Ca/44Ca) with typical reproducibilities of ± 40 and ± 16 ppm respectively (pooled 2 SD) for single (24 μg Ca) analyses. Multiple repeats yield mean values for terrestrial reference materials that are within their pooled 2 SE uncertainties of SRM 915a, to precisions of ± 15 and ± 6 ppm respectively. Measurements of mass-dependent Ca isotope variations (δ44/40Ca) have been made using a 42Ca-43Ca double spike isotope tracer together with measurements of 40Ca and 44Ca and have typical reproducibilities of ± 0.035 ‰ (pooled 2 SD) for single (12 μg) analyses. Measured δ44/40Ca values for reference materials are within uncertainty of previously reported values. Moreover, given that the double spike inversion uses the same isotopes as the mass independent determinations of 40Ca/44Ca and 43Ca/44Ca, our documentation of the absence of anomalies at a precision of better than 20 ppm in a range of low K/Ca terrestrial reference materials implies that the accuracy of our δ44/40Ca analyses is at this level of uncertainty.

Homonuclear ion-atom collisions: Application toLi+−Li

We present a theoretical framework for homonuclear, ground-state ion-atom collisions wherein the indistinguishability of direct elastic and resonant charge exchange (RCE) scattering channels is discussed. The discussion in terms of the total cross section(${\ensuremath{\sigma}}_{\text{tot}}$) is motivated and derived. The standard cross-section expressions for direct elastic(${\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\sigma}}}_{\text{el}}$) and RCE (${\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\sigma}}}_{\text{ce}}$) channels are obtained as high-energy approximations to ${\ensuremath{\sigma}}_{\text{tot}}$. We show that the total cross section resolves the inconsistency, at low energies, between the diffusion cross section (${\ensuremath{\sigma}}_{D}$) and the high-energy approximation to the total cross section (${\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\sigma}}}_{\text{tot}}$). The validity of the equivalence relation between the ${\ensuremath{\sigma}}_{D}$ and $2\ifmmode\times\else\texttimes\fi{}{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\sigma}}}_{\text{ce}}$ is also discussed. The differences which result in cross sections which are frequently used in the description of ion-atom collision is illustrated with specific calculations for an ${\mathrm{Li}}^{+}\ensuremath{-}\mathrm{Li}$ system. The use of ${\ensuremath{\sigma}}_{\text{tot}}$ is advocated as a correct and consistent way to represent cross sections.

On the stability of tangential discontinuity in the interaction of solar wind and cometary atmospheres

ABSTRACT In 2004, European Space Agency launched the spacecraft Rosetta. After almost 10-yr flight it arrived at the Churyumova–Gerasimenko comet. Rosetta was orbiting about the comet for some time observing its environment. One of the most interesting observations obtained during this mission was multiple disappearance of magnetic field. It was suggested that this phenomenon is related to the instability of cometopause, which is a tangential discontinuity separating the solar wind flow from the plasma component of the flow from a comet. In this article, we aim to study this instability. We numerically calculated the stationary state with the account of charge exchange on water molecules and resonant charge exchange. Then, we solved the non-stationary problem using the stationary state as the initial condition. We also studied the stability of the cometopause analytically in the short-wavelength approximation where we substituted the curved cometopause by a tangent plane. Both the numerical and analytical results show that the velocity jump at the cometopause is too weak to overtake the stabilizing effect of the magnetic field and cause the Kelvin–Helmholtz instability. We conclude that the main course of the cometopause instability is the charge exchange, and the instability is similar to the Rayleigh–Taylor instability that occurs in a gravitational field.

Distinctive Features of Charge Exchange Involving the Second Flavor of Hydrogen Atoms—The Candidates for Dark Matter

The second flavor of hydrogen atoms (SFHA) refers to the kind of hydrogen atoms that have only the states of the zero orbital angular momentum (the S-states), both in the discrete and continuous spectra. They were first discovered theoretically in one of my earlier papers, where a proof of their existence was also provided by analyzing atomic experiments concerning the high-energy tail of the linear momentum distribution in the ground state of hydrogen atoms. From a theoretical point of view, the discovery was based on the standard Dirac equation for hydrogen atoms without changing the existing physical laws. Recently, the existence of the SFHA was seemingly also confirmed by two types of astrophysical observations: the allowance for the SFHA explained the puzzling results concerning both the anomalous absorption of the redshifted 21 cm spectral line from the early Universe, and the observations by the Dark Energy Survey (DES) team where it was found that the distribution of dark matter in the Universe is noticeably smoother than predictions employing Einstein’s relativity. In the present review, we exhibit results from two recent papers where attention was brought to a visible difference in the cross-sections of the resonant charge exchange for collisions of the SFHA with incoming protons, compared to collisions of the usual hydrogen atoms with incoming protons. It was shown that, after taking into account the SFHA, there is a better agreement with the corresponding experimental cross-section. Coupled with the previous evidence of the existence of the SFHA, deduced from the analysis of the other kind of atomic experiments, and evidenced by two different kinds of astrophysical observations, this strengthens the standing of the SFHA as the most probable candidate for all or a part of dark matter.

Isotope selective three-step photoionization of 176Yb

Atomic vapor laser isotope separation of 176 Y b has been investigated through the density matrix analysis of laser–atom interactions in a three-step photoionization process. For the first time, to our knowledge, the method has been applied for both odd and even isotopes of Yb. The effects of peak power densities of the lasers, bandwidth of the excitation lasers, angular divergence, and number density of the atoms on the degree of enrichment have been studied. Peak power densities of the first, second, and third excitation lasers of 20, 20, and 40 , 000 W / c m 2 , respectively, and full angle divergence of the atomic beam of 120° were found to be optimum for the isotope separation of 176 Y b . The effects of resonant charge exchange collisions and atomic number densities on the degree of enrichment and production rates have also been studied. It has also been observed that the atomic number densities in the laser–atom interaction region should be limited to 1 × 1 0 12 a t o m s / c m 3 to obtain ∼ 90 % degree of enrichment of the 176 Y b isotope. At higher number densities of 1 × 1 0 13 a t o m s / c m 3 , the degree of enrichment decreases to 43.9%. The optimum range of bandwidths of excitation lasers is found be 90–120 MHz. At optimum conditions, the computed production rate of 22 mg/h is in good agreement with the previously reported value of 20 mg/h.

Classical Description of Resonant Charge Exchange Involving the Second Flavor of Hydrogen Atoms

We studied the consequences of the existence of the second flavor of hydrogen atoms (SFHA)—the existence proven by atomic experiments and evidenced by astrophysical observations—on the resonant charge exchange. We found analytically that there is indeed an important difference in the corresponding cross-sections for the SFHA compared to the usual hydrogen atoms. This difference could serve as an additional tool for distinguishing between the two kinds of hydrogen atoms in future experiments/observations. We also show that the SFHA does not exhibit any Stark effect—whether in a uniform or a non-uniform electric field—in any order of the perturbation theory.

Numerical research on ion extraction with resonant charge exchange process

The electric ion extraction, which plays an important role in productivity and abundance of product, is a critical step in laser isotope separation (LIS) technology. Several collision processes happen during the electric ion extraction, such as resonant and non-resonant charge exchange between ion and atom, the secondary ionization process and the ion-electron recombination. The resonant charge exchange process between target isotope ions and no-target background atoms is one of the major reasons of product contamination. As a result, the study of ion extraction with the consideration of resonant charge exchange process is essential. However, the resonant charge exchange process in ion extraction has not received enough attention. Besides, contradictory findings have been deduced in published studies. Therefore, it is necessary to clarify the effect of resonant charge exchange process in the electric ion extraction. In this article, the particle-in-cell (PIC) method and preprocessing hybrid-PIC method are adopted in both one- and two-dimensional numerical simulation. The preprocessing hybrid-PIC method is a calculation scheme by which accurate results can be obtained with less computational consumption. In this calculation scheme, the PIC method and hybrid-PIC method are used sequentially in different stages of ion extraction process. One-dimensional parallel type simulation cases are carried out under the circumstances of different initial plasma densities, applied voltages and background atom densities. The results show that the resonant charge exchange process happens in both shield layer and sheath layer. The ionic resonant charge exchange proportion in shield layer and sheath layer are related to the ion extraction time and average travel length in background vapor, respectively. Besides, they are proportional to the resonant charge exchange cross section and background atom density. And an empirical formula for deriving the resonant charge exchange ratio roughly is proposed. Two-dimensional simulations are carried out in four electrode configurations: parallel type, alternately biased parallel type, Π-type, and M-type. The extraction mechanisms are discussed and compared with each other. The simulation results show that M-type electrode configuration has the minimum resonant charge exchange ratio and extraction time among the configurations above. The results and conclusions provide an important reference for designing the LIS device.

REDISTRIBUTION OF SPUTTERED MATERIAL IN A PLANE IONPLASMA SYSTEM WITH AN ABNORMAL GLOW DISCHARGE

The redistribution of the flow of sputtered material of a target (cathode) between the collector and the target in a plane-parallel electrode system with an anomalous glow discharge is analyzed in the kinetic approximation. Sputtering is the result of bombardment of the target by gas ions accelerated in the near-cathode space charge layer and by fast neutral atoms formed as a result of resonant ion charge exchange. Sputtered atoms partially return to the target due to collisions with gas molecules. The formulas were obtained, which were confirmed in the experiment that makes it possible to correctly estimate the ratio of the sputtered material flows deposited on the collector and the target. The results of the work are used to calculate the parameters of the processes of coating deposition and ion cleaning of the target under conditions of the anomalous glow discharge.

Developments for pulsed antihydrogen production towards direct gravitational measurement on antimatter

A main scientific goal of the experiment is the direct measurement of the Earth’s local gravitational acceleration g on antihydrogen. The Weak Equivalence Principle is a foundation of General Relativity. It has been extensively tested with ordinary matter but very little is known about the gravitational interaction between matter and antimatter. Antihydrogen is produced in via resonant charge-exchange reaction between cold Rydberg-excited positronium and cooled down antiprotons. The achievements for the development of a pulsed cold antihydrogen source are presented. Large number of antiprotons, necessary for a significant production rate of antihydrogen, are captured, accumulated, compressed and cooled over an extended period of time. Positronium (Ps) is formed through e+-Ps conversion in a silica porous target at 10 K temperature in a reflection geometry inside the main apparatus. The so-formed Ps cloud is then laser-excited to Rydberg levels, for the first time in a 1 T magnetic field. Consequently, a detailed characterization of the Ps source for antihydrogen production in magnetic field needed to be performed. Several detection techniques are extensively used to monitor antiproton and positron manipulations in the formation process of antihydrogen inside the main apparatus. Positronium detection techniques underwent extensive improvements in sensitivity during the last antiproton run. At the same time, major efforts to improve integrate and commission the detectors sensitive to antihydrogen production took place.

Resonant Charge Exchange in an Electrostatic Field

The effect of an electrostatic field existing, for example, in plasma on the resonant charge exchange at collision velocities significantly lower than the charge exchange electron velocity is estimated using the small-radius potential model. It is established that the application of a field with a sufficient magnitude leads to a decrease in the charge exchange cross section. For example, in the case of the H– + H → H + H– reaction, a field of ∼107 V/cm decreases the charge exchange cross section by an order of magnitude.

Collisional cooling of trapped ions with cold atoms: results and insights

We present a series of recent experimental and numerical results which allow us to propose and explain the mechanisms for collisional cooling of a trapped ion by sequential binary collisions with atoms. Our experiments in hybrid atom-ion traps study the cooling of ions when the reservoir of the coolant atoms is spatially localized at the centre of the ion trap. Under these conditions the widely and long held expectation that for the ion to collisionally cool, the atom must be of lighter mass (i.e. mI > mA ) is overturned. Instead we show ion cooling for mI ⩽ mA in addition to mI > mA , and explain why earlier work establishing mass ratios does not apply to the experiments in hybrid traps. Further, for cooling of an ion A+ by the parent atom A, the mechanism of resonant charge exchange (RCE) allows for extremely efficient cooling of the ion A+. This mechanism is demonstrated by comparing the cooling rate of an ion with a localized ensemble of its parent atoms and with a lighter atomic species, where in the latter case the RCE mechanism does not exist. The difference in measured cooling rates for a given number density of the atoms and the theoretically calculated difference between elastic and RCE cross sections are used to show that the cooling efficiency per collision with RCE is much greater than the cooling by elastic collision. We conclude with some perspectives and prospects of future experiments.

Резонансная перезарядка в электростатическом поле

The estimation of the electrostatic field influence that exits, e.g., in plasma, on resonant charge exchange under collision velocities substantially less than that of an active electron is made in the frame of the zero range potential model. It is determined that the electric field of sufficient value leads to decreasing the charge exchange cross section. For example, the field about 10^7V/cm decreases the cross section on an order of magnitude.