Energetic Ions Research Articles

Multiscale numerical study of the ELM-induced sputtering on the tungsten castellated divertor gap

Material sputtering and erosion are key issue in fusion science. In the steady state, tungsten sputtering can be maintained at a low level. However, tungsten is seriously sputtered by the hot plasma from edge localized mode (ELM) bursts. The time evolution and spatial distribution of sputtering on the divertor gap are still not clear. This unclearness influences the understanding of ELM-induced sputtering and the explanation of experimental phenomenon. In this study, the evolution of tungsten flux generated by ELM burst is obtained via hybrid multiscale simulation and a double-peak of tungsten flux is found. The first peak is produced by the ELM electrons, which provides great sheath potential, and the second peak is generated by the energetic ions from ELM. The castellated divertor gap (CDG) can influence the tungsten sputtering distribution due to the change of the impacting angle. The sputtering and erosion on CDG are more serious than that on the mono-block top, but the tungsten source from the gap is very insignificant because the gap size is small. The simulation results are compared with EAST experiments and a qualitative consistency is obtained.

Demonstration of tritium adsorption on graphene.

In this work, we report on studies of graphene exposed to tritium gas in a controlled environment. The single layer graphene on a SiO2/Si substrate was exposed to 400 mbar of T2, for a total time of ∼55 h. The resistivity of the graphene sample was measured in situ during tritium exposure using the van der Pauw method. We found that the sheet resistance increases by three orders of magnitude during the exposure, suggesting significant chemisorption of tritium. After exposure, the samples were characterised ex situ via spatio-chemical mapping with a confocal Raman microscope, to study the effect of tritium on the graphene structure (tritiation yielding T-graphene), as well as the homogeneity of modifications across the whole area of the graphene film. The Raman spectra after tritium exposure were comparable to previously observed results in hydrogen-loading experiments, carried out by other groups. By thermal annealing we also could demonstrate, using Raman spectral analysis, that the structural changes were largely reversible. Considering all observations, we conclude that the graphene film was at least partially tritiated during the tritium exposure, and that the graphene film by and large withstands the bombardment by electrons from the β-decay of tritium, as well as by energetic primary and secondary ions.

The application of plasma technology for the preparation of supercapacitor electrode materials.

With the rapidly growing demand for clean energy and energy interconnection, there is an urgent need for rapid and high-capacity energy storage technologies to realize large-scale energy storage, transfer energy, and establish the energy internet. Supercapacitors, which have advantages such as high specific capacitance, fast charging and discharging rates, and long cycle lifetimes, are being widely used in electric vehicles, information technology, aerospace, and other fields. The performance of supercapacitors is crucially dependent on electrode materials. These can be categorized into electric double-layer capacitors and pseudocapacitors, primarily made from carbon and transition metal oxides, respectively. However, effectively monitoring the physicochemical properties of electrode materials during preparation and processing is challenging, which limits the improvement of supercapacitors' performance. Plasma materials preparation technology can effectively affect the materials preparation processing by energetic electrons, ions, free radicals, and multiple effects in plasma, which are easily manipulated by operation parameters. Therefore, plasma material preparation technology is considered a promising method to precisely monitor the physicochemical and electrochemical properties of energy storage materials and has been widely studied. This paper provides an overview of plasma materials preparation mechanisms, and details of the plasma technology application in the preparation of transition metal hybrids, carbon, and composite electrode materials, as well as a comparison with traditional methods. In conclusion, the advantages, challenges, and research directions of plasma materials preparation technology in the field of electrode materials preparation are summarized.

A Novel Backtracing Model to Study the Emission of Energetic Neutral Atoms at Titan

AbstractTo study the emission of energetic neutral atoms (ENAs) at Titan, we have developed a novel model that takes into account a spacecraft detector's limited field of view and traces energetic magnetospheric particles backward in time. ENAs are generated by charge exchange between Titan's atmospheric neutrals and energetic magnetospheric ions. By tracing these ions through the draped electromagnetic fields in Titan's environment, we generate synthetic ENA images and compare them to Cassini observations from the TA flyby. Our model can reproduce the intensity and morphology of the observed images only when field line draping is included. Using a realistic detector geometry is necessary to determine the influence of this draping on the ENA images: the non‐uniform fields eliminate a localized feature of increased ENA flux, which is a different effect than in models utilizing an infinitely extended detector. We demonstrate that ENA observations from TA contain signatures of the time‐varying Saturnian magnetospheric environment at Titan: the modeled ENA emission morphology and the effect of field line draping are different for the background field vectors measured during the inbound and outbound legs of TA. The visibility and qualitative effect of the draping on observed ENA images vary strongly between different detector locations and pointings. Depending on the viewing geometry, field line draping may add segments of elevated flux to the synthetic ENA images, remove such segments, or have no qualitative effect at all. Our study emphasizes the challenges and the potential for remote sensing of Titan's interaction region using ENA imaging.

Study on damage of Gd2O3-CeO2 under electronic energy loss: comparison between bulk-like and nanostructure.

To understand the physical phenomena responsible for radiation damage of the materials used in nuclear reactors, and thus study their operation life and/or efficiency, it is required to simulate the conditions by exposing the materials to energetic ions. Ceria (CeO2) has been proposed as one of the inert matrices for the transmutation of minor actinides in the futuristic inert matrix fuel (IMF) concept. The inert matrix should also contain burnable poison to compensate for the initial reactivity of fuel. In this context, gadolinium (Gd) is an excellent burnable poison with a high neutron absorption cross-section. In view of this, Gd2O3-CeO2 nano-powders were synthesized and sintered at 800 °C and 1300 °C to obtain different grain sizes and morphologies. FESEM and TEM were carried out to study the grain size of pristine pellets. The sintered pellets were irradiated with 80-MeV Ag ions (electronic energy loss (Se) regime) at room temperature to emulate the effect of fission fragments. For analysis of the effect of grain size on the irradiation-induced structural degradation at different fluences, GIXRD and Raman spectroscopy were performed. Significantly large damage has been observed for the smaller grain-sized samples (sintered at 800 °C) as compared to the large grain-sized sample (sintered at 1300 °C). Neither of the samples amorphized under the present experimental conditions as indicated by the presence of the Raman-active T2g mode (centred at 462 cm-1) and all the XRD peaks of fluorite cubic structure up to the highest fluence employed (1 × 1014 ions cm-2). X-ray photoelectron spectroscopy results demonstrate that Ce4+ to Ce3+ and vacancy-related isolated clusters are the main defects produced in the systems. The radiation tolerance behaviour of the samples is understood with the help of thermal spike simulation, which indicates higher transient lattice temperatures with longer duration in the smaller grain-sized sample upon irradiation. Gd-doped ceria thus possesses good radiation stability in the Se regime, indicating its potential for application in IMFs.

Exploration on the Possible Bump-on-Tail Instability in VASIMR

The bump-on-tail (BOT) instability is generally caused by a beam of energetic particles existing in relatively cold background plasma. The employment of second-stage wave-driven module in the variable specific impulse magnetoplasma rocket (VASIMR) yields the production of energetic ions, which could drive the BOT instability. The present work explores this possibility for the first time via numerical simulations based on the experimental data on the VASIMR, i.e., referring to VX-50. It is found that the BOT instability does exist even in the plume region away from antenna. The results indicate that velocity space diffusion provides a stabilizing effect on the nonlinear evolution of waves, while dissipation in the bulk plasma essentially impedes it. To show the practical values implied by these computations, the influences of this BOT instability on the power coupling and thrust are investigated particularly. These findings are valuable for VASIMR, as well as other plasma thrusters that yield energetic particles inside relatively cold background plasma, to suppress BOT instability and thus increase the power coupling efficiency and thrust performance.

Modeling terahertz emissions from energetic electrons and ions in foil targets irradiated by ultraintense femtosecond laser pulses.

Terahertz (THz) emissions from fast electron and ion currents driven in relativistic, femtosecond laser-foil interactions are examined theoretically. We first consider the radiation from the energetic electrons exiting the backside of the target. Our kinetic model takes account of the coherent transition radiation due to these electrons crossing the plasma-vacuum interface as well as of the synchrotron radiation due to their deflection and deceleration in the sheath field they set up in vacuum. After showing that both mechanisms tend to largely compensate each other when all the electrons are pulled back into the target, we investigate the scaling of the net radiation with the sheath field strength. We then demonstrate the sensitivity of this radiation to a percent-level fraction of escaping electrons. We also study the influence of the target thickness and laser focusing. The same sheath field that confines most of the fast electrons around the target rapidly sets into motion the surface ions. We describe the THz emission from these accelerated ions and their accompanying hot electrons by means of a plasma expansion model that allows for finite foil size and multidimensional effects. Again, we explore the dependencies of this radiation mechanism on the laser-target parameters. Under conditions typical of current ultrashort laser-solid experiments, we find that the THz radiation from the expanding plasma is much less energetic-by one to three orders of magnitude-than that due to the early-time motion of the fast electrons.

Improving the accuracy of ion implantation simulations through the use of DFT-MD methodology

Ion implantation is a crucial process in the fabrication of semiconductor devices, but accurately predicting the impurities distribution in the low energy range is still challenging. The widely used method to simulate this process is molecular dynamics with recoil interaction approximation (RIA-MD), which uses the translational method to replace traditional periodic boundary conditions. However, this approach leads to accuracy loss due to the simplification of atom-atom interactions and bulk crystal properties. Our study presents a method to simulate the impurity distribution after ion implantation at low energy, which combines all-electron density-functional theory (DFT) and full molecular dynamics (MD). Unlike the RIA-MD method, DFT-MD method calculates the movements of all energetic ions and simulates the whole bulk crystal properties. Thus, it provides a more realistic representation of atom-atom interactions. We used not only the experimental values reported by references but also the experimental value measured by actual ion implantation technology samples. This enabled us to make a more accurate comparison between the DFT-MD and RIA-MD methods. Specifically, the dopant profiles and amorphous thickness obtained using the DFT-MD method were found to be in good agreement with experimental data. These findings demonstrate the effectiveness of our method and highlight its potential to advance the field of ion implantation simulation. Moreover, our method has the potential to be useful in developing atomic-scale technology computer-aided design (TCAD) tools, as well as in other fields of research that require accurate ion implantation simulations.

Ti-Al-C Based MAX Phase Coating As Corrosion Protection for Ferritic Bipolar Plates

Metallic bipolar plates in fuel cells have the advantages of high electrical conductivity, low permeability to the reactants and gases, and easy manufacturability. However, resistance to corrosion under long term operation conditions limits their practical use in the fuel cell. Owing to the importance of corrosion stability, materials such as austenitic stainless steels, Ni-based alloys and coated titanium or stainless steel plates are currently being used in bipolar plates, although ferritic steels would be cost effective. A pinhole-free anticorrosion coating can help in application of the ferritic steels in fuel cells. MAX phase materials offer excellent corrosion stability and high electronic conductivity and have been successfully tested for corrosion protection of metallic bipolar plates. In the current work, Ti-Al-C-based MAX phase coatings were prepared using high power impulse magnetron sputtering (HiPIMS). The HiPIMS process was in some cases also combined with plasma immersion ion implantation (PIII) to study the influence of the high energetic ion implantation process on the structure and performance of the resulting MAX phase layer. The deposited samples were annealed at 800 °C for 2 h in Ar atmosphere. The structure and composition of the coatings produced were studied with X-ray photoelectron spectroscopy, atom probe tomography and transmission electron microscopy. The corrosion performance of the layers was studied using a scanning flow cell coupled with inductively coupled plasma mass spectroscopy.

Aging of Plasma-Activated Polyethylene and Hydrophobic Recovery of Polyethylene Polymers.

Available literature on the aging of plasma-activated polyethylene due to hydrophobic recovery has been reviewed and critically assessed. A common method for the evaluation of hydrophobic recovery is the determination of the static water contact angle, while the surface free energy does not reveal significant correlations. Surface-sensitive methods for the characterization of chemical composition and structure have limited applicability in studying the aging phenomenon. Aging is driven by thermodynamics, so it is observed even upon storage in a vacuum, and hydrophobic recovery increases with increasing temperature. Storage of plasma-activated polyethylene in the air at ambient conditions follows almost logarithmic behavior during the period studied by most authors; i.e., up to one month. The influence of the storage medium is somehow controversial because some authors reported aging suppression by storing in polar liquids, but others reported the loss of hydrophilicity even after a brief immersion into distilled water. Methods for suppressing aging by hydrophobic recovery include plasma treatment at elevated temperature followed by brief treatment at room temperature and application of energetic ions and photons in the vacuum ultraviolet range. Storing at low temperatures is a trivial alternative, but not very practical. The aging of plasma-activated polyethylene suppresses the adhesion of many coatings, but the correlation between the surface free energy and the adhesion force has yet to be addressed adequately.

Molecular dynamics simulation of 100 keV argon ion radiation effects in metals and comparison with stopping and range of ions in matter code

Simulation is essential to analyse radiation-induced effects because energetic ions have short transit times within materials (Ar ions of 1 keV and 100 keV have transit times of 0.29 picoseconds and 29 femtoseconds respectively, through a 25 nm Al film). The binary collision approximation (BCA) is extensively used in simulations to study damage caused by energetic ions due to its computational efficiency. Stopping and Range of Ions in Matter (SRIM), a widely used Monte Carlo software using BCA, provides accurate ion ranges consistent with experiments. Molecular dynamics simulations are powerful computational method, where classical equations of motion are solved to track atomic movements from radiation damage, but computational resources required are heavier for this method. In our current effort, the energy transfer from 100 keV Ar+ to metal targets is analysed as a function of target properties, including melting temperature and atomic density, using these two methodologies. A detailed investigation of 100 keV Ar+ ion impact on metal targets is done using the classical Molecular Dynamics simulation program ‘MDRange’, which uses the Recoil Interaction Analysis (RIA) approximation, where the interaction between the ion and its closest neighbours is considered via a two-body potential. The correlation of energy transferred to the metal with the target properties is examined considering the physical approximations of each technique.

Optimization of the collective Thomson scattering diagnostic for the GDT open magnetic trap

The collective Thomson scattering of high-power millimeter-wave radiation on plasma density fluctuations (CTS) is widely used for diagnosing the velocity distribution function of energetic ions in fusion plasma. In this paper, we discuss a non-standard scheme of CTS measurements, which exploits strong refraction of probing and scattered microwave beams when reflecting from the cut-off layer in dense plasma. The scheme may be realized with the existing CTS diagnostic system at the Gas-Dynamic Trap (GDT) facility, a large open magnetic trap operating at Budker Institute (Novosibirsk, Russia). This requires a minor upgrade of the available hardware and essentially increases the range of plasma densities allowed for CTS measurements, as well as its sensitivity and spatial resolution. A detailed study of CTS efficiency for different geometries and plasma conditions at GDT is performed by means of an advanced numerical model that allows for an accurate description of non-Gaussian beam scattering in inhomogeneous plasma. To perform this task, we develop a quasi-optical theory of scattering, which itself may be of general interest.

Study of particle dynamics in presence of ring current driven magnetic field variations

The development of the ring current through a westward circulation of energetic ions around the Earth in the low latitude region during geomagnetic storms has been known to us for the past several decades. The symmetric part of the ring current exists in the form of a ring around the Earth at a distance of ≈3–7Re from the center of the Earth. The location and strength of the ring current is mainly controlled by the interplanetary solar wind conditions. The presence of such external current forms the additional mini magnetic dipole in the vicinity of the Earth’s space, which eventually affects the geomagnetic field configuration. The magnetic field produced due to the ring current opposes the geomagnetic field inside and adds to the geomagnetic field outside the location of the ring current. This scenario has been modelled in this paper by using a circular loop of uniform current around the Earth to represent the ring current flow around the Earth. The aim of the present study is to understand the overall changes in the magnetic field and its influence on the radiation belt energetic (MeV range) electrons and protons during a geomagnetic storm. The model calculations suggest the formation of low and high magnetic field regions (here referred to as dent and hump) in the Earth’s magnetosphere due to intense westward ring current. The size and position of these low and high magnetic field regions are controlled by the strength and location of the ring current. It is found that both the altitudinal reach and mirror point of the bouncing-drifting radiation belt energetic particles are significantly affected by the presence of the dent and the hump in the magnetic field driven by the ring current. The decrease in ground magnetic field of 1700 nT or more, which is similar to the geomagnetic field variation observed during the historic Carrington event, is possible with the peak ring current strength of 20–30 MA situated at a distance of 2Re or less from the center of the Earth.

Swift heavy ion irradiation of polyaniline-graphene nanocomposite films: Structural and optical properties

In this study, we investigate the use of swift heavy ions to modify the structural and optical properties of PANI-graphene nanocomposite (PANI-G NC) films. PANI-G NC films were synthesized on Indium Tin Oxide (ITO)-coated glass by electrochemical polymerization of aniline in the presence of CVD-grown graphene. The films were then irradiated with 36 MeV Cu8+ ions at fluences between 5.4 × 1012 and 6.4 × 1013 ions/cm2. SEM results show that irradiation up to 1.6 × 1013 ions/cm2 leads to the formation of a porous interconnected network, with graphene nanoparticles adhering to the PANI matrix. Beyond this fluence, a dense and compact granular structure appears. Raman spectroscopy reveals enhanced Raman scattering of the polaronic lattice and the introduction of defects in graphene. At fluences exceeding 2.1 × 1013 ions/cm2, the obtained spectra reveal a distinctive broad envelope centered at the D and G positions of graphene, characteristic of nanocrystalline graphite. X-ray diffraction shows an increase in both crystallinity and crystallite size of the PANI-G NC film with increasing fluence, followed by a decrease beyond a critical ion fluence. Optical modifications were characterized by a red shift in the UV–Vis spectrum with increased fluence. The optical band gap shows a decreasing trend with ion dose, attributed to the formation of carbonaceous clusters along the latent tracks of energetic ions. In short, this study demonstrates that swift heavy ion irradiation could be an effective tool for enhancing the structural and optical properties of PANI-G NC films and tailoring them for specific applications.

Antibacterial Plasma Polymer Coatings on 3D Materials for Orthopedic Applications

AbstractCovalent biofunctionalization of implant surfaces using anti microbial agents is a promising approach to reducing bone infection and implant failure. Radical‐rich, ion‐assisted plasma polymerized (IPP) coatings enable surface covalent biofunctionalization in a simple manner; but until now, they are limited to only 2D surfaces. Here a new technology is demonstrated to create homogenous IPP coatings on 3D materials using a rotating, conductive cage that is negatively biased while immersed in RF plasma. Evidence is provided that under controlled energetic ion bombardment, this technology enables the formation of highly robust and homogenous radical‐rich coatings on 3D objects for subsequent covalent attachment of antimicrobial agents. To functionally apply this technology, the broad‐spectrum antimicrobial CSA‐90 is attached to the surfaces, where it retained potent antibacterial activity against Staphylococcus aureus. CSA‐90 covalent functionalization of stainless‐steel pins used in a murine model of orthopedic infection revealed the highly promising potential of this coating system to reduce S. aureus infection‐related bone loss. This study takes the previous research on plasma‐based covalent functionalization of 2D surfaces a step further, with important implications for ushering in a new dimension in the biofunctionalization of 3D structures for applications in bone implants and beyond.

Thinning of Poly(methyl methacrylate) and Poly(vinyl chloride) Thin Films Induced by High-Energy Ions of Different Stopping Powers.

Ion bombardment is an important tool of materials processing, but usually leads to erosion of the surface and significant thickness reductions when thin layers are used. The growing use of polymer thin films in a variety of applications, from coatings and membranes to biomedical and electronic devices, calls for a deeper understanding of the thinning process induced by energetic ions espe-cially for very thin films. Here, thinning and surface morphology changes induced by high-energy ion bombardment in PMMA and PVC thin films were investigated, focusing on the role of the initial thickness of the films and the stopping power of the ions. We used thin films with initial thicknesses varying from 13 to 800 nm, and light and heavy ions as projectiles in the energy range of 2-2000 MeV, where the electronic stopping dominates. Thickness reductions as a function of fluence were monitored and thinning cross sections were extracted from curves. A supralinear scaling between the thinning cross sections and the electronic stopping power of the beams was observed, with a much enhanced thinning efficiency for the swift heavy ions. The scaling with the stopping power dE/dx is almost independent of the initial thickness of the films. At intermediate and large fluences, changes in the physicochemical properties of the irradiated polymers may modulate and decelerate the thinning process of the remaining film. The importance of this secondary process depends on the stopping power and the balance between erosion and the chemical transformations induced by the beam. We also observe a trend for the thinning efficiency to become larger in very thin films. Depending on the type of beam and polymer, this effect is more or less pronounced. PMMA films irradiated with 2 MeV H+ show the most systematic correlation between initial thickness and thinning cross sections, while in PVC films the initial thickness plays a minor role for all investigated beams.

Predictive modeling of Alfvén eigenmode stability in inductive scenarios in JT-60SA

The JT-60SA device offers unique conditions before ITER for the study of the interaction of energetic particles with plasma waves. With similar dimensions to JET, e.g., a major radius but with a slightly more elongated plasma volume, JT-60SA is used as a high-power device where additional heating power (including 10 MW of the 500 keV Neutral Beam Injection) of up to 41 MW and the potential for high non-inductive plasma current operation pave the path for numerous challenges in physics on MHD stability, in particular, when considering the effects of energetic particles. Several operational scenarios with ITER and DEMO-relevant plasma regimes, in terms of non-dimensional plasma parameters, are anticipated. In this work, the stability of Alfvén eigenmodes (AEs) in variants of two of the most relevant operational scenarios with single null is analyzed: a full Ip inductive scenario at high density (1.1 × 1020 m−3 on-axis electron density) and 5.48MA/2.05T toroidal plasma current and magnetic field, and an advanced (hybrid) scenario with an ion energy transport barrier (ITB) and 3.5MA/2.28T toroidal plasma current and magnetic field. The workflow included the CRONOS code to establish the scenario, the ASCOT code to calculate the slowing-down energetic particle distributions for a positive/negative ion source-based neutral beam, and the MISHKA/CASTOR-K suite to calculate the MHD spectra of AEs and the associated drive/damping contributions from the NBI energetic ions, as well as the thermal ion landau damping. The systematic analysis, over a large Fourier space of the toroidal mode number/mode frequency, provides evidence that although a significant fraction of supra-Alfvénic particles stemming from the negative ion source-based neutral beam (500 keV) can, in some cases, drive to AEs in both scenarios, it is not enough to overcome the thermal ion landau damping. In addition, the advanced scenario with ITB is shown to be stable against AEs localized in the vicinity of the barrier as well, offering good prospects of sustainability of the plasma performance and of ITB. Finally, some sensitivity scan results are shown on the influence of fast ion density and q-profile on the AE mode spectra and stability.

Analyses of ∼0.05–2 MeV Ions Associated with the 2022 February 16 Energetic Storm Particle Event Observed by Parker Solar Probe

We present analyses of 0.05–2 MeV ions from the 2022 February 16 energetic storm particle event observed by Parker Solar Probe's (PSP) IS⊙IS/EPI-Lo instrument at 0.35 au from the Sun. This event was characterized by an enhancement in ion fluxes from a quiet background, increasing gradually with time with a nearly flat spectrum, rising sharply near the arrival of the coronal mass ejection (CME)–driven shock, becoming nearly a power-law spectrum, then decaying exponentially afterward, with a rate that was independent of energy. From the observed fluxes, we determine diffusion coefficients, finding that far upstream of the shock the diffusion coefficients are nearly independent of energy, with a value of 1020 cm2 s−1. Near the shock, the diffusion coefficients are more than 1 order of magnitude smaller and increase nearly linearly with energy. We also determine the source of energetic particles, by comparing ratios of the intensities at the shock to estimates of the quiet-time intensity to predictions from diffusive shock acceleration theory. We conclude that the source of energetic ions is mostly the solar wind for this event. We also present potential interpretations of the near-exponential decay of the intensity behind the shock. One possibility we suggest is that the shock was overexpanding when it crossed PSP and the energetic particle intensity decreased behind the shock to fill the expanding volume. Overexpanding CMEs could well be more common closer to the Sun, and this is an example of such a case.

Computational approach to identify structural and elastic relationship in metastable crystalline and amorphous alloy thin films: Mo1-xNix and Mo1-xSix case studies

Previously well-established experimental trends of ground-state properties of crystalline and amorphous Mo1-xSix and Mo1-xNix alloys with 0 ≤ x ≤ 1 are predicted by first-principles calculations and inter-relationship with sound velocities and elastic properties are identified. The free energy of mixing, calculated at 300 K provides accurate values of the critical Si and Ni concentrations leading to the crystalline-to-amorphous transition. Specifically, a transition from BCC to amorphous state is predicted for xSi ~ 0.14 and xNi ~ 0.32, while FCC to amorphous transition is observed for xNi ~ 0.77. These structural transitions are accompanied by modifications of the out-of-plane longitudinal and shear elastic constants. In the crystalline region, a pronounced softening of elastic moduli is predicted for both solid solution alloys. While for amorphous Mo-Ni, the elastic constants do not undergo significant changes, for amorphous Mo-Si, they exhibit two distinct behaviors depending on the electronic properties and bonding character. For 0.2 ≤ xSi ≤ 0.7, the metallic character of the amorphous alloys is maintained and the elastic properties are remarkably stable. For xSi > 0.7, a progressive increase in the atomic volume is observed and the amorphous alloys acquire a covalent character and a reduced coordination number. Surprisingly, during this transition, both the longitudinal and shear acoustic velocities continuously increase, despite a progressive softening of the elastic stiffness constants. These calculations provide deep insight at the atomic-scale and reproduce satisfactorily the earlier experimental works of magnetron co-sputtered Mo-Si films, while some disagreement on elastic properties remain for more energetic ion beam sputtered Mo-Ni films, likely partially attributed to point-defects.

3D Monte-Carlo simulation of Ganymede’s atmosphere

We present new model results for H2O, O2, H2, O, and H in the atmosphere of Ganymede. The results are obtained from a collision-less 3D Monte-Carlo model that includes sublimation, ion and electron sputtering, and ion and electron radiolysis. Because Ganymede has its own magnetic field, its immediate plasma environment is particularly complex. The interaction between Ganymede’s and Jupiter’s magnetospheres makes it highly variable in both space and time. The recent Juno Ganymede flyby provided us with new data on the electron local environment. Based on the electron measurements recorded by the Jovian Auroral Distributions Experiment (JADE), we implement two electron populations, one for the moon’s polar regions and one for the moon’s auroral regions. Comparing the atmospheric contribution of these newly defined electron populations to the overall source and loss processes is one of the main goals of this work.Our analysis shows that for H2O, sublimation remains the most important source process even after accounting for the new electron populations, delivering more than three orders of magnitude more H2O molecules to the atmosphere than all other source processes combined. The source fluxes for O2 and H2, on the other hand, are dominated by radiolysis induced by the auroral electrons, assuming that the electron fluxes JADE measured during Juno’s transit of Ganymede’s magnetopause current layer are representative of auroral electrons. Atomic O and H are mainly added to the atmosphere through the dissociation of O2 and H2, which is primarily induced by auroral electrons.Our understanding of Ganymede’s atmosphere today is mainly based on spectroscopic observations. The interpretation of spectroscopic data strongly depends on assumptions taken, though. Our analysis shows that for a holistic understanding of Ganymede’s atmosphere, simultaneous observations of the moon’s surface, atmosphere, and full plasma environment (thermal and energetic ions and electrons) at different times and locations (both with respect to Ganymede and with respect to Jupiter) are particularly important. Such measurements are planned by ESA’s Jupiter ICy moons Explorer (JUICE), in particular by the Particle Environment Package (PEP), which will greatly advance our understanding of Ganymede and its atmosphere and plasma environment.