Charge Exchange Processes Research Articles

New Interacting Boson Fermion-Fermion Model results

We present a new application of the Interacting Boson Model (IBM) and its extensions for describing double charge exchange reactions. The study of double charge exchange reactions induced by heavy ions involving candidate nuclei for neutrinoless double beta decay is a complex task carried out by the NUMEN collaboration. This investigation faces the intricacies of complex oddodd intermediate nuclei in sequential double charge exchange processes. We will offer a comprehensive description of heavy odd-odd nuclei using the Interacting Boson Fermion-Fermion Model (IBFFM). Additionally, we will outline the methodology for describing transfer operators within this framework. Finally, we will explore the potential applications of our results for describing double charge exchange reactions.

Experimental measurement of state selective double electron capture in collision between 1.4–20 keV/u Ar<sup>8+</sup> with He

Electron capture in the collision of highly charged ions with atoms and molecules is a fundamental process related to the electron transition between bound states belonging to two atomic-centers. The X-ray emission after electron capture is important for X-ray astrophysical modeling, fusion plasma diagnostics, and ion irradiated biophysics. In the past few decades, momentum-imaging cold-target recoil ion momentum spectroscopy has been a significantly developed technique and widely used to measure the quantum state-selective population in electron capture processes. Based on the cold target recoil ion momentum spectroscopy installed on the 150 kV highly charged ion platform in Fudan University, Shanghai City, China, the state-selectivity of double electron capture in the bombardment of 1.4–20 keV/u Ar<sup>8+</sup> on He is measured, and the relative cross sections of the 3l3l<i>'</i> to 3l7l<i>'</i> double excited states are obtained. It is found that with the increase of collision energy, more quantum state-selectivity channels are open in the double electron capture (DEC) of Ar<sup>8+</sup>-He collision. It is also found that the relative cross section of the quantum state population is strongly dependent on the collision energy of the projectile ion. The present measurements not only enrich the state-selective cross-sectional library and collision dynamics of highly charged ion charge exchange processes, but also provide experimental benchmarks for existing theoretical calculations.

Self-consistent multi-component simulation of plasma turbulence and neutrals in detached conditions

Simulations of high-density deuterium plasmas in a lower single-null magnetic configuration based on a TCV discharge are presented. We evolve the dynamics of three charged species (electrons, D+ and D2+ ), interacting with two neutrals species ( D and D2 ) through ionization, charge-exchange, recombination and molecular dissociation processes. The plasma is modelled by using the drift-reduced fluid Braginskii equations, while the neutral dynamics is described by a kinetic model. To control the divertor conditions, a D2 puffing is used and the effect of increasing the puffing strength is investigated. The increase in fuelling leads to an increase of density in the scrape-off layer and a decrease of the plasma temperature. At the same time, the particle and heat fluxes to the divertor target decrease and the detachment of the inner target is observed. The analysis of particle and transport balance in the divertor volume shows that the decrease of the particle flux is caused by a decrease of the local neutral ionization together with a decrease of the parallel velocity, caused by the lower plasma temperature and the increase in momentum losses. The relative importance of the different collision terms is assessed, showing the crucial role of molecular interactions, as they are responsible for increasing the atomic neutral density and temperature, since most of the D neutrals are produced by molecular activated recombination and D2 dissociation. The presence of strong electric fields in high-density plasmas is also shown, revealing the role of the E × B drift in setting the asymmetry between the divertor targets. Simulation results are in agreement with experimental observations of increased density decay length, attributed to a decrease of parallel transport, together with an increase of plasma blob size and radial velocity.

Nonclassical Mechanism of Metal-Enhanced Photoluminescence of Quantum Dots.

Metal-enhanced photoluminescence is able to provide a robust signal even from a single emitter and is promising in applications in biosensors and optoelectronic devices. However, its realization with semiconductor nanocrystals (e.g., quantum dots, QDs) is not always straightforward due to the hidden and not fully described interactions between plasmonic nanoparticles and an emitter. Here, we demonstrate nonclassical enhancement (i.e., not a conventional electromagnetic mechanism) of the QD photoluminescence at nonplasmonic conditions and correlate it with the charge exchange processes in the system, particularly with high efficiency of the hot-hole generation in gold nanoparticles and the possibility of their transfer to QDs. The hole injection returns a QD from a charged nonemitting state caused by hole trapping by surface and/or interfacial traps into an uncharged emitting state, which leads to an increased photoluminescence intensity. These results open new insights into metal-enhanced photoluminescence, showing the importance of the QD surface states in this process.

Fast and cold negative ion and neutral atom beams from a water spray

High-power lasers are routinely used to generate energetic positively charged ions, and this paper reports on the observation of negative ions in these experiments. A large number of negative ions and neutral atoms at MeV energies was obtained from the interaction of a high intensity laser pulse with a water spray along with positive ions [Abicht et al., Appl. Phys. Lett. 103, 253501 (2013)]. Beams of negative ions and neutral atoms have the same properties as beams of positive ions. However, the mechanism of negative ion formation and acceleration is still under discussion. In order to gain more information about physics of generation negative ions and neutrals, we present a new experiment where all species, positive, negative ions, and neutrals, are spatially separated, and the electron capture and loss of each in water spray is evaluated. The formation of negative ions and neutral atoms of hydrogen and carbon with energies up to 140 keV and 1.2 MeV, respectively, is confirmed. It is suggested that the electrification of spray droplets plays a decisive role in these charge-exchange processes.

Charge exchange processes during carbon ion fragmentation at an energy of 300 MeV/nucleon: comparison with models of ion-ion interactions

Experimental data are presented on the differential cross sections to produce 11Be, 12Be, and 12B isotopes at the carbon beam fragmentation with an energy of 300 MeV/nucleon in the FRAGM experiment conducted based on the ITEP-TWAС multipurpose accelerator complex. The obtained experimental data are compared with the predictions of the models of ion-ion interactions: binary cascade and quantum molecular dynamics model.

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.

The role of charge-exchange processes in probing hydrogen plasma with a heavy ion beam

Charge-changing processes of low-charged ions, used in hydrogen plasma probing by the heavy ion beam probe method, are considered. Along with the ionization of beam ions by plasma electrons and protons, the charge-exchange processes of ions on H atoms and protons are also studied. It is shown that charge exchange of beam ions on plasma protons and H atoms, which is rarely taken into account, plays an important role in beam–plasma interaction. New data on the cross sections and rates of ionization and charge-exchange processes are presented for Tl+ and Tl2+ ions, which are frequently used for plasma diagnostics. Calculations are performed for hydrogen plasma temperatures Te = 1 eV–10 keV and densities Ne = 1012–1014 cm−3 at relatively low and high ion-beam velocities vb = 0.2 and 1.0 a.u., respectively. Special attention is paid to the determination of the electron temperatures at which the charge-exchange processes on H atoms and protons are important. Multiple ionization of beam ions by plasma electrons and protons is briefly discussed.

Influence of Wettability and Geometry on Contact Electrification between Nonionic Insulators.

Contact electrification is an interfacial process in which two surfaces exchange electrical charges when they are in contact with one another. Consequently, the surfaces may gain opposite polarity, inducing an electrostatic attraction. Therefore, this principle can be exploited to generate electricity, which has been precisely done in triboelectric nanogenerators (TENGs) over the last decades. The details of the underlying mechanisms are still ill-understood, especially the influence of relative humidity (RH). Using the colloidal probe technique, we convincingly show that water plays an important role in the charge exchange process when two distinct insulators with different wettability are contacted and separated in <1 s at ambient conditions. The charging process is faster, and more charge is acquired with increasing relative humidity, also beyond RH = 40% (at which TENGs have their maximum power generation), due to the geometrical asymmetry (curved colloid surface vs planar substrate) introduced in the system. In addition, the charging time constant is determined, which is found to decrease with increasing relative humidity. Altogether, the current study adds to our understanding of how humidity levels affect the charging process between two solid surfaces, which is even enhanced up to RH = 90% as long as the curved surface is hydrophilic, paving the way for designing novel and more efficient TENGs, eco-energy harvesting devices which utilize water and solid charge interaction mechanism, self-powered sensors, and tribotronics.

Strongly perturbed state-selective charge exchange between slowAr8+and He

We report an experimental and theoretical study of state-selective charge exchange processes in ${\mathrm{Ar}}^{8+}$ on He collisions at 1 and 3 keV/amu, benchmarking the fundamental electron capture dynamics under strong perturbations. The quantum-state selectivity has been experimentally resolved for one $1s$ electron of He capture into $4s$, $4p$, $4d+4f$, and $5s$ states of ${\mathrm{Ar}}^{7+}$ ion along with the corresponding scattering angle differential cross sections. By comparing to theoretical calculations with a two-active-electron semiclassical asymptotic-state close-coupling approach, we are able to verify the important role of electronic correlations during the collisions and that the impact parameter sensitive transition probability significantly mediates the state-selective specifics.

A United Triboelectrification Mechanism for Contacts between All Types of Materials

AbstractTriboelectrification for contacts between three types of materials—metals, polymers, and semiconductors—are investigated. The results show that triboelectrification is a charge exchange process between the surfaces of two friction materials, and its output is the synergetic effects of the electrostatic induction (ESI) and dynamic junction modulation (DJM). There are four current/voltage peaks in output of triboelectrification: two of them are attributed to the ESI effect and determined by the surface state densities and electron affinity difference of the materials, while the other two are associated with the DJM effect and determined by the charging exchange between the surface states and the depletion region. However, metals and polymers have no‐modulation of depletion region due to their high conductivity and insulating nature, respectively, thus only two peaks induced by the ESI effect are observable no matter what types of metals and polymers are in pair for contacting. Semiconductors have a depletion region, there will be two more output current/voltage peaks induced by the junction modulation when a semiconductor is in contact with any type of materials. The observations reveal a universal triboelectrification mechanism for contacts between materials, and provide an intuitive guidance for the development of high‐performance triboelectric nanogenerators.

Testing a prediction model for the H-mode density pedestal against JET-ILW pedestals

The neutral ionisation model proposed by Groebner et al (2002 Phys. Plasmas 9 2134) to determine the plasma density profile in the H-mode pedestal, is extended to include charge exchange processes in the pedestal stimulated by the ideas of Mahdavi et al (2003 Phys. Plasmas 10 3984). The model is then tested against JET H-mode pedestal data, both in a ‘standalone’ version using experimental temperature profiles and also by incorporating it in the Europed version of EPED. The model is able to predict the density pedestal over a wide range of conditions with good accuracy. It is also able to predict the experimentally observed isotope effect on the density pedestal that eludes simpler neutral ionization models.

Ion thruster accelerator grid erosion mechanism under extreme conditions of cylindrical erosion and chamfer erosion

In this paper, the abnormal experimental phenomenon on barrel erosion under extreme working conditions in the ultra-long life experiment (>10000 h) of ion thruster ion optics is studied by the Immersed-Finite-Element Particle-In-Cell Monte-Carlo-Collision (IFE-PIC-MCC) method and the grid erosion evaluation model. The transport process of beam ions and Charge Exchange (CEX) ions in the grid system, and the characteristics and mechanisms of the aperture barrel erosion under extreme erosion conditions (i.e. the cylindrical erosion and chamfer erosion) were systematically studied. Thanks to the advantage of the IFE method for dealing with complex boundaries in structured mesh, the aperture barrel erosion morphology of the accelerator grid is reconstructed accurately based on the experimental results. The results show that, with the evolution of working conditions, the mechanism of the aperture barrel erosion changes significantly, which relies heavily on the accelerator grid morphology. The change of the accelerator grid aperture barrel morphology has a significant effect on the behavior of CEX ions, and only affects the local electric field distribution, but has no effect on the upstream plasma sheath. As the erosion progresses, the erosion position moves downstream along the grid aperture axis direction, and the erosion range becomes narrower. Regardless of the erosion phase, the erosion rate of the CEX ions located downstream of the decelerator grid is the largest. The erosion rate is related to the mean incident energy and angle, and their variation is closely related to the position and trajectory of CEX ions.

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.

Electron Spectroscopy of Charge Exchange Effects in Low Energy Ion Scattering at Surfaces: Case Studies of Heavy Ions at Al Surface

This work discusses studies of electron emissions during the interaction of low energy (in the keV energy range and below) singly charged ions with Aluminum surfaces. Analysis of the spectra provides insight into the electronic excitation processes and the dynamics of the interaction of the projectiles with the surface excitation. The work is primarily focused on the clarification of the role of electron promotion in charge exchange processes that occur during the cascade of atomic collisions. The work highlights the importance of the solid environment and of electron correlation in the understanding of charge exchange and energy deposition in ion-solids interactions.

Quantifying Effects Of Final State Interactions On Pion Production In DUNE Using Monte Carlo Event Generators

The analysis of pion production in neutrino-nucleus scattering is crucial to quantify the effect of final state interactions (FSI) in the energy regime of DUNE and other long-baseline neutrino experiments since FSI modify the number of pions that emerge in the final state as compared to the number of pions produced in the initial (primary) state. Not only the number of pions but also their charge gets changed due to the prevailing FSI effects. In the present work, we will study the effect of FSI on pions after their production at the initial neutrino-nucleus interaction vertex using two different Monte Carlo (MC) simulation tools viz. GENIE (version: 3.0.6) and NuWro (version: 19.2.2). Considering the DUNE experimental set-up, we observe pion production in νµ and 40 Ar nucleus interactions for an event sample of 1 million for each generator. We find that there are some differences in the pion number observed in the primary and final states of two generators and that the differences are above statistical fluctuations. We observe that GENIE (version: 3.0.6) is more responsive (less transparent) to absorption and charge exchange processes as compared to NuWro (version: 19.2.2).

ARSENY: A program for computing inelastic transitions via hidden crossings in one-electron atomic ion–ion collisions with classical description of nuclear motion

The ARSENY program is intended to compute cross-sections of inelastic transitions via hidden crossings upon slow one-electron atomic ion–ion collisions using the approximation of classical description of nuclear motion in the collision energy region E<20 KeV/nucleon. Particular attention is paid to the calculation of the analytical properties of adiabatic potential energy curves of the two-center Coulomb problem for complex values of the internuclear distance. Complex branch points and hidden crossings are calculated and their significance for the dynamics of one-electron collisional systems is revealed. Benchmark calculations of cross sections for charge exchange, excitation, and ionization in slow He2++H(1s) collisions are presented and compared with experimental data. Program summaryProgram Title: ARSENYCPC Library link to program files:https://doi.org/10.17632/n43srxwdnm.1Licensing provisions: CC By 4.0Programming language: FORTRAN 90/95. Compilers: Intel(R) Visual Fortran Compiler 19.0.4.245 [IA-32]Nature of problem: The processes of charge exchange, excitation, and ionization in one-electron atomic ion–ion collisions in a low-temperature plasma are actively studied in astrophysics and tokamak Charge-eXchange Recombination Spectroscopy (CXRS) Edge diagnostics in ITER [1–7]. Numerical calculations of cross sections for charge exchange, excitation, and ionization for slow one-electron atomic ion–ion collisions within the approximation of classical description of nuclear motion have been conventionally implemented, in particular, by the electron-nuclear dynamics approach [8] and the close-coupled channel method using basis functions of the two-center Coulomb problem (see, e.g., [9–13]). However, with real-valued internuclear distance these approaches did not allow for the dynamical structure of discrete-discrete and discrete-continuous transitions in the two-center Coulomb problem. This disadvantage manifests itself in the disagreement between the theoretical and experimental cross-sections at small velocity of ions [13–15]. In a number of papers [1,14,16–20] the dynamical structure of the transitions is considered in terms of hidden crossing of potential curves, when using the analytic continuation to a complex plane of the internuclear distance. This approach is implemented in the ARSENY program aimed at computing cross sections of inelastic discrete-discrete and discrete-continuous transitions via hidden crossings for slow one-electron atomic ion–ion collisions within the approximation of classical description of nuclear motion announced in [1]. Benchmark calculations of cross sections for charge exchange, excitation, and ionization in slow He2++H(1s) collisions are presented and compared with experimental data.Solution method: The potential energy curves E=E(R) and the separation constant λ=λ(R) depending on the real-valued and complex-valued parameter R of the two-center Coulomb problem are calculated from the minimization condition for a quadratic functional corresponding to a pair of nonlinear equations with respect to a pair of unknowns E(R) and λ(R) by iterating three-term recurrent relations [21,22] using a mean least square method [23]. These equations are obtained from the known recurrent relations for the expansion coefficients of quasiradial and quasiangular spheroidal Coulomb functions. The series of branching points Rc sought for in the complex plane of internuclear distance R and the hidden crossings of complex potential energy curves E(R) are calculated by an iterative method using the known analytical behavior in the form of a square root of difference E(R)−E(Rc) in the vicinity of the unknown branch points Rc. Calculations of cross-sections of inelastic transitions via hidden crossings for the slow one-electron atomic ion–ion collisions within the approximation of classical description of nuclear motion are carried out by integration over the impact parameter of the nonadiabatic transition probability expressed in terms of the Stückelberg parameter determined integral of difference of imaginary parts of each pair of complex potential energy curves E(R) by a contour around the branching point Rc [18,19].Additional comments including restrictions and unusual features: In calculations of cross sections and required branch points, about 220 adiabatic states of the lower part of the discrete spectrum of the two-center problem are used.

Energetic Neutral Atom Imaging of the Earth’s Ring Current and Some Results from the Chinese Double Star Program

The ring current region in the Earth’s magnetosphere contains energetic charged particles, which are injected from the magnetotail, get trapped in the inner magnetosphere, and finally drift around the Earth. The current, essentially carried by ions, is caused by the differences between the drift of the positively charged ions and that of negatively charged electrons. The charge exchange that occurs between ring current ions and geocoronal atoms determines the distribution and evolution of the ring current and lays the basis for remote detection techniques. By measuring the energetic neutral atoms produced by the charge-exchange process, the ring current can be remotely detected via energetic neutral atom imaging. The Chinese Double Star Program operated the NeUtral Atom Detector Unit (NUADU) onboard one of its two satellites for more than four years. A variety of studies were conducted using multiple methods applied to observations, such as intuitive image inspection, forward modeling, and inversion. Energetic neutral atom imaging was established as a promising technique for future imaging projects.

Fast electron contribution in electronic stopping for p-He and p-Ar collisions

Our study has shown that in collisions p-He and p-Ar with energies above 50 keV fast electrons carry away as kinetic energy up to 70 % of energy released during particle stopping. Ignoring the fast electron contribution makes impossible bringing independently measured cross sections of elementary processes of ionization, excitation, stripping and charge exchange into compliance with measured cross sections of electronic stopping. Fast electron emission in collisions of energetic ions with solids may induce extra radiation effects (create additional vacancies and defects in solid).Mean kinetic energies of ejected electrons We obtained from the analysis of cross section ratio agree well with directly measured energy spectra of the emitted electrons. The dynamic ionization theory implies the We proportionality to initial velocity v. In the considered cases, such a dependence takes place at the velocities below 2 a.u. At higher velocities, the observed dependence is successfully described in the framework of the Born approximation.

A liquid hydrogen target to fully characterize the new MEG II liquid xenon calorimeter

The MEG II experiment aims to improve the sensitivity to μ+→e+γ down to 6×10−14, surpassing the 4.2×10−13 UL by MEG. To achieve this sensitivity the detector performances need to be assessed and monitored via dedicated calibrations. To calibrate the Liquid Xenon Calorimeter near the signal energy (52.8 MeV), photons are produced through the Charge EXchange (CEX) process π−p→nπ0(→γγ). Here we present the liquid Hydrogen target used for the CEX run 2021, during the first MEG II physics run.