Incoming Ions Research Articles

On performance capacity of plasma optical mass separator

In the magnetic barrier of the azimuthator of the POMS-E-3 plasma optical mass separator, a 20–40 times decrease in the ion flux has been observed. Such a phenomenon deems the process of separation of a multi-component ion beam into elements inefficient. Upon conducting an in-depth theoretical analysis of the problem regarding the passage of the ion stream across the magnetic barrier while considering the walls and in the absence of those, it has been concluded that the problem has a unique steady-state solution allowing for the ions to pass at any values of magnetic field induction, regardless of the density and thermal dispersion in the incoming ion beam. The maximum value of the ion density at the output of the magnetic barrier is estimated as n∞∼β1πW0e2Δ2, where W0 stands for the ion energy at the input of the magnetic barrier and Δ equals the length of the magnetic barrier, while e signifies the electron charge and β varies from 1/9 to 1.

In-situ observation of an irradiation creep deformation mechanism in zirconium alloys

We report an original experimental study on a zirconium alloy deformed in situ under ion irradiation and applied stress inside a Transmission Electron Microscope. We observe that dislocations initially pinned on irradiation defects can be unpinned and glide at a lower stress under the effect of the irradiation. It is proposed that unpinning occurs by a local effect of the displacement cascade created by the incoming ion in the vicinity of the pinning point. This novel mechanism of dislocation glide assisted by irradiation is thought to play a crucial role on in-reactor irradiation creep of zirconium alloys.

Formation of a highly doped ultra-thin amorphous carbon layer by ion bombardment of graphene

Ion bombardment of graphene leads to the formation of defects which may be used to tune properties of the graphene based devices. In this work, however, we present that the presence of the graphene layer on a surface of a sample has a significant impact on the ion bombardment process: broken sp2 bonds react with the incoming ions and trap them close to the surface of the sample, preventing a standard ion implantation. For an ion bombardment with a low impact energy and significant dose (in the range of 1014 atoms cm−2) an amorphization of the graphene layer is observed but at the same time, most of the incoming ions do not penetrate the sample but stop at the surface, thus forming a highly doped ultra-thin amorphous carbon layer. The effect may be used to create thin layers containing desired atoms if no other technique is available. This approach is particularly useful for secondary ion mass spectrometry where a high concentration of Cs at the surface of a sample significantly enhances the negative ionization probability, allowing it to reach better detection limits.

Low-energy particle experiments\u2013ion mass analyzer (LEPi) onboard the ERG (Arase) satellite

Low-energy ion experiments–ion mass analyzer (LEPi) is one of the particle instruments onboard the ERG satellite. LEPi is an ion energy-mass spectrometer which covers the range of particle energies from < 0.01 to 25 keV/q. Species of incoming ions are discriminated by a combination of electrostatic energy-per-charge analysis and the time-of-flight technique. The sensor has a planar field-of-view, which provides 4pi steradian coverage by using the spin motion of the satellite. LEPi started its nominal observation after the initial checkout and commissioning phase in space.

Consequences of atomic layer etching on wafer scale uniformity in inductively coupled plasmas

Atomic layer etching (ALE) typically divides the etching process into two self-limited reactions. One reaction passivates a single layer of material while the second preferentially removes the passivated layer. As such, under ideal conditions the wafer scale uniformity of ALE should be independent of the uniformity of the reactant fluxes onto the wafers, provided all surface reactions are saturated. The passivation and etch steps should individually asymptotically saturate after a characteristic fluence of reactants has been delivered to each site. In this paper, results from a computational investigation are discussed regarding the uniformity of ALE of Si in Cl2 containing inductively coupled plasmas when the reactant fluxes are both non-uniform and non-ideal. In the parameter space investigated for inductively coupled plasmas, the local etch rate for continuous processing was proportional to the ion flux. When operated with saturated conditions (that is, both ALE steps are allowed to self-terminate), the ALE process is less sensitive to non-uniformities in the incoming ion flux than continuous etching. Operating ALE in a sub-saturation regime resulted in less uniform etching. It was also found that ALE processing with saturated steps requires a larger total ion fluence than continuous etching to achieve the same etch depth. This condition may result in increased resist erosion and/or damage to stopping layers using ALE. While these results demonstrate that ALE provides increased etch depth uniformity, they do not show an improved critical dimension uniformity in all cases. These possible limitations to ALE processing, as well as increased processing time, will be part of the process optimization that includes the benefits of atomic resolution and improved uniformity.

A study to compute integrated dpa for neutron and ion irradiation environments using SRIM-2013

Displacements per atom (dpa), estimated based on the standard Norgett–Robinson–Torrens (NRT) model, is used for assessing radiation damage effects in fast reactor materials. A computer code CRaD has been indigenously developed towards establishing the infrastructure to perform improved radiation damage studies in Indian fast reactors. We propose a method for computing multigroup neutron NRT dpa cross sections based on SRIM-2013 simulations. In this method, for each neutron group, the recoil or primary knock-on atom (PKA) spectrum and its average energy are first estimated with CRaD code from ENDF/B-VII.1. This average PKA energy forms the input for SRIM simulation, wherein the recoil atom is taken as the incoming ion on the target. The NRT-dpa cross section of iron computed with “Quick” Kinchin-Pease (K-P) option of SRIM-2013 is found to agree within 10% with the standard NRT-dpa values, if damage energy from SRIM simulation is used. SRIM-2013 NRT-dpa cross sections applied to estimate the integrated dpa for Fe, Cr and Ni are in good agreement with established computer codes and data. A similar study carried out for polyatomic material, SiC, shows encouraging results. In this case, it is observed that the NRT approach with average lattice displacement energy of 25 eV coupled with the damage energies from the K-P option of SRIM-2013 gives reliable displacement cross sections and integrated dpa for various reactor spectra. The source term of neutron damage can be equivalently determined in the units of dpa by simulating self-ion bombardment. This shows that the information of primary recoils obtained from CRaD can be reliably applied to estimate the integrated dpa and damage assessment studies in accelerator–based self-ion irradiation experiments of structural materials. This study would help to advance the investigation of possible correlations between the damages induced by ions and reactor neutrons.

A Generalized Approach to Model the Spectra and Radiation Dose Rate of Solar Particle Events on the Surface of Mars

Abstract For future human missions to Mars, it is important to study the surface radiation environment during extreme and elevated conditions. In the long term, it is mainly galactic cosmic rays (GCRs) modulated by solar activity that contribute to the radiation on the surface of Mars, but intense solar energetic particle (SEP) events may induce acute health effects. Such events may enhance the radiation level significantly and should be detected as immediately as possible to prevent severe damage to humans and equipment. However, the energetic particle environment on the Martian surface is significantly different from that in deep space due to the influence of the Martian atmosphere. Depending on the intensity and shape of the original solar particle spectra, as well as particle types, the surface spectra may induce entirely different radiation effects. In order to give immediate and accurate alerts while avoiding unnecessary ones, it is important to model and well understand the atmospheric effect on the incoming SEPs, including both protons and helium ions. In this paper, we have developed a generalized approach to quickly model the surface response of any given incoming proton/helium ion spectra and have applied it to a set of historical large solar events, thus providing insights into the possible variety of surface radiation environments that may be induced during SEP events. Based on the statistical study of more than 30 significant solar events, we have obtained an empirical model for estimating the surface dose rate directly from the intensities of a power-law SEP spectra.

In-depth study of in-trap high-resolution mass separation by transversal ion ejection from a multi-reflection time-of-flight device.

The recently introduced method of ion separation by transversal ejection of unwanted species in electrostatic ion-beam traps and multi-reflection time-of-flight devices has been further studied in detail. As this separation is performed during the ion storage itself, there is no need for additional external devices such as ion gates or traps for either pre- or postselection of the ions of interest. The ejection of unwanted contaminant ions is performed by appropriate pulses of the potentials of deflector electrodes. These segmented ring electrodes are located off-center in the trap, i.e., between one of the two ion mirrors and the central drift tube, which also serves as a potential lift for capturing incoming ions and axially ejecting ions of interest after their selection. The various parameters affecting the selection effectivity and resolving power are illustrated with tin-cluster measurements, where isotopologue ion species provide mass differences down to a single atomic mass unit at ion masses of several hundred. Symmetric deflection voltages of only 10 V were found sufficient for the transversal ejection of ion species with as few as three deflection pulses. The duty cycle, i.e., the pulse duration with respect to the period of ion revolution, has been varied, resulting in resolving powers of up to several tens of thousands for this selection technique.

Interface roughening in irradiated oxide dispersion strengthened steels

Oxide Dispersion Strengthened steels are considered as promising candidates for nuclear applications as cladding tubes for GEN IV reactors. These materials are reinforced by a fine dispersion of nano-oxides whose semi-coherent flat interfaces constitute trapping sites for radiation-induced point defects. However, the sink strength of such interfaces may change under irradiation since the interfaces become damaged themselves. Therefore, the behavior of semi-coherent flat interfaces under irradiation is under concern. After ion irradiation up to 150 dPa at 500 °C, High Resolution Transmission Electron Microscopy images show that interfaces are no longer sharp but present an irregular mound morphology owing to the destabilization by the nuclear cascade collisions of incoming ions. Further, the kinetic roughening of the interfaces appears to increase with the irradiation dose. However, the low magnitude of the roughness suggests that the interfaces are remarkably stable under irradiation.

Ring-averaged ion velocity distribution function probe for laboratory magnetized plasma experiment.

Ring-averaged velocity distribution function of ions at a fixed guiding center position is a fundamental quantity in the gyrokinetic plasma physics. We have developed a diagnostic tool for the ring averaged velocity distribution function of ions for laboratory plasma experiments, which is named as the ring-averaged ion distribution function probe (RIDFP). The RIDFP is a set of ion collectors for different velocities. It is designed to be immersed in magnetized plasmas and achieves momentum selection of incoming ions by the selection of the ion Larmor radii. To nullify the influence of the sheath potential surrounding the RIDFP on the orbits of the incoming ions, the electrostatic potential of the RIDFP body is automatically adjusted to coincide with the space potential of the target plasma with the use of an emissive probe and a voltage follower. The developed RIDFP successfully measured the equilibrium ring-averaged velocity distribution function of a laboratory magnetized plasma, which was in accordance with the Maxwellian distribution having an ion temperature of 0.2 eV.

Two-stream instabilities from the lower-hybrid frequency to the electron cyclotron frequency: application to the front of quasi-perpendicular shocks

Abstract. Quasi-perpendicular supercritical shocks are characterized by the presence of a magnetic foot due to the accumulation of a fraction of the incoming ions that is reflected by the shock front. There, three different plasma populations coexist (incoming ion core, reflected ion beam, electrons) and can excite various two-stream instabilities (TSIs) owing to their relative drifts. These instabilities represent local sources of turbulence with a wide frequency range extending from the lower hybrid to the electron cyclotron. Their linear features are analyzed by means of both a dispersion study and numerical PIC simulations. Three main types of TSI and correspondingly excited waves are identified: i. Oblique whistlers due to the (so-called fast) relative drift between reflected ions/electrons; the waves propagate toward upstream away from the shock front at a strongly oblique angle (θ ∼ 50°) to the ambient magnetic field Bo, have frequencies a few times the lower hybrid, and have wavelengths a fraction of the ion inertia length c∕ωpi. ii. Quasi-perpendicular whistlers due to the (so-called slow) relative drift between incoming ions/electrons; the waves propagate toward the shock ramp at an angle θ a few degrees off 90°, have frequencies around the lower hybrid, and have wavelengths several times the electron inertia length c∕ωpe. iii. Extended Bernstein waves which also propagate in the quasi-perpendicular domain, yet are due to the (so-called fast) relative drift between reflected ions/electrons; the instability is an extension of the electron cyclotron drift instability (normally strictly perpendicular and electrostatic) and produces waves with a magnetic component which have frequencies close to the electron cyclotron as well as wavelengths close to the electron gyroradius and which propagate toward upstream. Present results are compared with previous works in order to stress some features not previously analyzed and to define a more synthetic view of these TSIs.

Intrinsic Challenges in Creating a Reversible Copper(II) Fluoride Cathode for Lithium-Ion Batteries

Copper(II) fluoride (CuF2) is a promising cathode material for the next generation of lithium-ion batteries due to its high theoretical gravimetric (1645 Wh·kg-1) and volumetric (3797 Wh·L-1) energy density. In theory, it can reversibly store two incoming lithium ions in what is referred to a conversion reaction (2 Li+ + CuF2 + 2 e- → 2 LiF + Cu0). Although near-theoretical capacity (~515 mAh·g-1) has been achieved for the first discharge, capacity greatly decreases with every cycle thereafter. This is surprising as materials such as iron(II) fluoride, which undergo a similar reaction (2 Li+ + FeF2 + 2 e- → 2 LiF + Fe0) can easily achieve 10 cycles without any major capacity degradation. The lack of reversible capacity in CuF2 may be due to irreversible crystal structure changes inside of cathode which inhibit delithiation upon charging or due to the loss of copper through the electrolyte. Evidence for the latter for this can be seen through the copper plating of the lithium metal anode after cycling, detected by energy dispersive x-ray spectroscopy (EDS) analysis, or through the decrease in copper peak intensity in X-ray diffraction (XRD) and EDS spectra of the cathodes upon recharging. Correlation of copper content to capacity suggests that copper loss from the cathode is not the only factor in capacity loss and scanning electron microscopy (SEM) imaging shows large morphological differences between a pristine and charged sample. Decoupling these two intrinsic challenges for CuF2 batteries will enable the design of more reversible conversion reaction cathode materials in the future. For now, application of CuF2 in primary lithium-ion batteries remains promising, and continues to be expanded upon today. This work is supported by the U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy (EERE) program under Award No. DE-EE0006852.

A W-Geometry Ortho-TOF MS with High Resolution and Up to 100% Duty Cycle for MS/MS.

Orthogonal injection time-of-flight (orthoTOF) mass spectrometry (MS) is the most prevalent form of TOFMS, owing to its greater control over incoming ion energy, the ability to correct for aberrations in incoming ion velocity and position, and its ability to provide an entire mass spectrum within a single scan. However, the duty cycle of orthoTOFMS is low compared with scanning analyzers, which can have 100% duty cycle when measuring a single type of ion. Typical duty cycles for orthoTOFMS range from 1% to 30%, depending on instrument geometry. Generally, as instrument resolution increases, duty cycle decreases. Additionally, the greatest duty cycle is achieved for the highest m/z ion recorded in the spectrum, and decreases for all other ions as a function of m/z. In a prior publication [Loboda, A.V.; Chernushevich, I.V. J. Am. Soc. Mass Spectrom. 20, 1342-1348 (20)], a novel trapping/release method for restoring the duty cycle of a V-geometry orthoTOFMS to near 100% (referred to as "Zeno pulsing") was presented. Here, we apply that method to a W-TOF geometry analyzer with analog detection. Across a m/z range of 100-2000, sensitivity gains of ~5-20 are observed, for total ion currents approaching ~107 ions·s-1. Zeno pulsing, or similar strategies for restoring duty cycle, will continue to be important as instrument resolution in orthoTOFMS is increased through the use of ion mirrors. Graphical Abstract ᅟ.

Factors controlling the reactivity of divalent metal ions towards pheophytin a

In this study, we evaluate the factors which determine the reactivity of divalent metal ions in the spontaneous formation of metallochlorophylls, using experimental and computational approaches. Kinetic studies were carried out using pheophytin a in reactions with various divalent metal ions combined with non- or weakly-coordinative counter ions in a series of organic solvents. To obtain detailed insights into the solvent effect, the metalations with the whole set of cations were investigated in three solvents and with Zn2+ in seven solvents. The reactions were monitored using electronic absorption spectroscopy and the stopped-flow technique. DFT calculations were employed to shed light on the role of solvent in activating the metal ions towards porphyrinoids. This experimental and computational analysis gives detailed information regarding how the solvent and the counter ion assist/hinder the metalation reaction as activators/inhibitors. The metalation course is dictated to a large extent by the reaction medium, via either the activation or deactivation of the incoming metal ion. The solvent may affect the metalation in several ways, mainly via H-bonding with pyrrolenine nitrogens and the activation/deactivation of the incoming cation. It also seems to affect the activation enthalpy by causing slight conformational changes in the macrocyclic ligand. These new mechanistic insights contribute to a better understanding of the “metal–counterion–solvent” interplay in the metalation of porphyrinoids. In addition, they are highly relevant to the mechanisms of metalation reactions catalyzed by chelatases and explain the differences between the insertion of Mg2+ and other divalent cations.

Substrate Bias Dependent Microstructure and Properties of TC17 Titanium Alloy Coatings Deposited by Magnetron Sputtering

While matrix coated fiber method is used to fabricate SiC continuous fiber reinforced TC17 (Ti-5Al-2Sn-2Zr-4Mo-4Cr) matrix composites (SiCf/TC17), the properties of SiCf/TC17 composite are strongly affected by the microstructure and properties of TC17 alloy coatings in precursor wires. In this work, Vb(substrate bias) was adopted to tailor the microstructure and properties of TC17 coatings, and Vb dependent on microstructure, morphology, composition, stress, hardness and adhesion for TC17 coatings have been investigated by X-ray diffraction, scanning electron microscope, atomic force microscope, auger electron spectrometer, surface profiler and nanoindenter. The experimental results showed that all coatings crystallized with hexagonal structure (α-Ti). The migratory ability of incoming ions increased with increasing Vb from floating to-120V, and the smoothing growth surface and re-sputtering came into prominence with further increasing Vb, then the surface roughened again and accompanied by a transition of growth mode from column grains to compact-grain structures. As Vb increased, Al content increased while Ti content decreases. In addition, compressive stress and hardness showed a rising trend caused by ions implantation. Interface ions implantation and stress state acted together on the adhesive force between TC17 alloy coatings and SiC fiber.

Multi-scale modelling to relate beryllium surface temperature, deuterium concentration and erosion in fusion reactor environment

Beryllium (Be) has been chosen as the plasma-facing material for the main wall of ITER, the next generation fusion reactor. Identifying the key parameters that determine Be erosion under reactor relevant conditions is vital to predict the ITER plasma-facing component lifetime and viability. To date, a certain prediction of Be erosion, focusing on the effect of two such parameters, surface temperature and D surface content, has not been achieved. In this work, we develop the first multi-scale KMC-MD modeling approach for Be to provide a more accurate database for its erosion, as well as investigating parameters that affect erosion. First, we calculate the complex relationship between surface temperature and D concentration precisely by simulating the time evolution of the system using an object kinetic Monte Carlo (OKMC) technique. These simulations provide a D surface concentration profile for any surface temperature and incoming D energy. We then describe how this profile can be implemented as a starting configuration in molecular dynamics (MD) simulations. We finally use MD simulations to investigate the effect of temperature (300–800 K) and impact energy (10–200 eV) on the erosion of Be due to D plasma irradiations. The results reveal a strong dependency of the D surface content on temperature. Increasing the surface temperature leads to a lower D concentration at the surface, because of the tendency of D atoms to avoid being accommodated in a vacancy, and de-trapping from impurity sites diffuse fast toward bulk. At the next step, total and molecular Be erosion yields due to D irradiations are analyzed using MD simulations. The results show a strong dependency of erosion yields on surface temperature and incoming ion energy. The total Be erosion yield increases with temperature for impact energies up to 100 eV. However, increasing temperature and impact energy results in a lower fraction of Be atoms being sputtered as BeD molecules due to the lower D surface concentrations at higher temperatures. These findings correlate well with different experiments performed at JET and PISCES-B devices.

Coverage threshold for laser-induced lithography

Recent experimental observations of laser-induced adsorption at the interface between an alkali vapor and a dielectric surface have demonstrated the possibility of growing metallic films of nanometric thickness on dielectric surfaces, with arbitrary shapes determined by the intensity profile of the light. The mechanisms directly responsible for the accumulation of atoms at the irradiated surface have been shown to involve photo-ionization of atoms very close to the surface. However, the existence of a vapor-pressure threshold for initiating the film growth still raises questions on the processes occurring at the surface. In this letter, we report on the observation that the vapor-pressure threshold corresponds to a minimum adatom coverage necessary for the surface to effectively neutralize the incoming ions and make possible the growth of a multilayer film. We discuss the hypothesis that the coverage threshold is a surface conductivity threshold.

Formation of Fe-Co-Si Structure in Fe and Co Implanted Si Substrate

ABSTRACTTernary Fe-Co-Si B20 phase structure was formed by implanting Fe and Co ions consecutively into Si(100) substrate at 50 keV energy, each with a fluence of 1.0 × 1017 atoms/cm2 and post-thermal vacuum annealing at 500 oC for 60 minutes. An in-situ magnetic field was used to enhance the formation of the ternary phase in the Si substrate during the implantation process. The magnetic field of 0.05 T was applied perpendicular to the incoming ion beam direction and parallel to the substrate surface to form elongated clusters in the transverse direction of the sample. Prior to the implantation of ions, the implant ions depth profiles were simulated using a dynamic ion-solid interaction code (TRIDYN). The TRIDYN simulation predicted a saturation in the peak concentration of the Fe and Co ions at a fluence of 1.0 × 1017 atoms/cm2. XPS measurement at the peak concentration depth (40 nm) showed the presence of Fe (23 %) and Co (32 %) in the Si matrix. XRD characterization confirmed the presence of stable Fe-Co-Si B20 phase structure in the annealed samples implanted with the in-situ magnetic field.

Application of corona discharge-generated air ions for filtration of aerosolized virus and inactivation of filtered virus

The effect of corona discharge-generated air ions on the filtration of aerosolized bacteriophage MS2 was studied. A carbon-fiber ionizer was installed upstream of a medium-efficiency air filter to generate air ions, which were used to charge the virus aerosols and increase their filtration efficiency. After the virus aerosols were captured by the filter for a certain time interval, they were exposed to a newly incoming air ion flow. Captured virus particles were detached from the filter by sonication, and their antiviral efficiency due to air ions was calculated by counting the plaque-forming units. The antiviral efficiency increased with ion exposure time and ion concentration. When the concentration of positive air ions was 107ions/cm3, the antiviral efficiencies were 46.1, 78.8, and 83.7% with exposure times of 15, 30, and 45min, respectively. When the ionizer was operated in a bipolar mode, the number concentrations of positive and negative ions were 6.6×106 and 3.4×106ions/cm3, respectively, and the antiviral efficiencies were 64.3, 89.1, and 97.4% with exposure times of 15, 30, and 45min, respectively. As a quantitative parameter for the performance evaluation of air ions, the susceptibility constant of bacteriophage MS2 to positive, negative, bipolar air ions was calculated as 5.5×10−3, 5.4×10−3 and 9.5×10−3, respectively. These susceptibility constants showed bipolar ion treatment was more effective about 1.7 times than unipolar ion treatment.

Local charge exchange of He+ ions at Aluminum surfaces

We report on experiments designed to observe the correlation between the autoionization of doubly excited helium atoms and the Auger decay of 2p vacancies in Al. The autoionizing states are formed when incident He+⁎ and He++ are neutralized by resonant electron capture at the surface. 2p excitation in Al occurs in dielectronic charge transfer during the close encounter of an excited helium ion and an Al atom. These results clarify the mechanism for Al-2p excitation in the case of singly charged ground state He+(1s) ion impact, where the dielectronic transition occurs after promotion of the 1s electron of incoming ions.