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As surface-only materials, freestanding 2D materials are known to have a high level of contamination—mostly in the form of hydrocarbons, water, and residuals from production and exfoliation. For well-designed experiments, it is of particular importance to develop effective cleaning procedures, especially since standard surface science techniques are typically not applicable. We perform ion spectroscopy with highly charged ions transmitted through freestanding atomically thin materials and present two techniques to achieve clean samples, both based on thermal treatment. Ion charge exchange and energy loss are used to analyze the degree of sample contamination. We find that even after cleaning, heavily contaminated spots remain on single layer graphene. The contamination coverage, however, clusters in strand-like structures leaving large clean areas. We present a way to discriminate clean from contaminated areas with our ion beam spectroscopy if the heterogeneity of the surface is increased sufficiently enough. We expect a similar discrimination to be necessary in most other experimental techniques. [ABSTRACT FROM AUTHOR]

The porosity of the upper layers of regolith is key to the interaction of an airless planetary body with precipitating radiation, but it remains difficult to characterize. One of the effects that is governed by regolith properties is Energetic Neutral Atom (ENA) emission in the form of reflected and neutralized solar wind protons. We simulate this process for the surface of the Moon by implementing a regolith grain stacking in the ion‐solid‐interaction software SDTrimSP‐3D, finding that proton reflection significantly depends on the regolith porosity. Via comparison with ENA measurements by Chandrayaan‐1, we derive a globally averaged porosity of the uppermost regolith layers of 0.85−0.14+0.15 $0.8{5}_{-0.14}^{+0.15}$. These results indicate a highly porous, fairy‐castle‐like nature of the upper lunar regolith, as well as its importance for the interaction with impacting ions. Our simulations further outline the possibility of future regolith studies with ENA measurements, for example, by the BepiColombo mission to Mercury. Plain Language Summary: The Moon's surface is covered with regolith, a soil made up of stacked grains. Properties of this regolith influence how the Moon interacts with its environment. One example of such an effect are impact by charged particles emitted from the Sun called the "solar wind." We now present simulations of the reflection of such particles from the surface of the Moon, taking into account the grain structure of the regolith. We only find an agreement between the simulations and spacecraft measurements of reflected solar wind particles for very loosely stacked grains. Overall, the amount of reflected particles significantly depends on the structure of the regolith. Our simulations predict that 85% of the volume in the regolith is made up of empty space between grains. These results thus show how measurements of reflected particles can be applied for studying soil properties of the Moon, as well as other planetary bodies such as Mercury. Key Points: Reflection of solar wind protons from lunar regolith is simulated with SDTrimSP‐3DA precise agreement with spacecraft measurements of energetic neutral atom emission is only found for highly porous regolith structuresA lunar regolith porosity of 0.85−0.14+0.15 $0.8{5}_{-0.14}^{+0.15}$ is derived from solar wind proton reflection, which could also be applied to other airless bodies [ABSTRACT FROM AUTHOR]

Investigating the space weathering of the Martian moon Phobos represents an important step toward understanding the development from its origin to its present‐day appearance. Depending on Phobos' orbital position, its surface is continuously sputtered by the solar wind and planetary ions that originate in the Martian atmosphere. Based on Mars Atmosphere and Volatile Evolution measurements, it has been proposed that sputtering by planetary O+ and O2+ ions dominates in the Martian tail region, where the planet mostly shadows Phobos from the solar wind. In these models, uncertainties for sputtering yield inputs still exist due to the lack of sufficient analog experiments. Therefore, sputtering measurements with O+, O2+, C+, and CO2+ ions between 1 and 5 keV were performed using augite samples as Phobos analogs. The experimental results for O+ irradiations show smaller mass changes than predicted by SDTrimSP simulations, which probably can be attributed to O implantation enabled by the Fe content of the target. Sputtering with O2+ and CO2+ in the low keV range shows no deviations in the sputtering yields attributable to molecular effects. Therefore, CO2+ ions will most likely be negligible for the sputtering of Phobos according to the current understanding of ion fluxes on the Martian moon. Ultimately, our experiments suggest that the sputtering contribution on Phobos by O ions is about 50% smaller than previously assumed. This does not change the qualitative outcome from previous modeling stating that planetary O ions are by far the dominant sputtering contribution on Phobos in the Martian tail region. Plain Language Summary: The surface of the Martian moon Phobos is continuously eroded by positively charged ions in a process called sputtering, which has changed the moon's surface over the past billions of years. Previous calculations suggest that this sputtering is caused by ions from the solar wind as well as oxygen ions that reach Phobos from the atmosphere of Mars. However, there exists a significant lack of data on how much sputtering each ion causes. This study presents laboratory experiments where the erosion of Phobos analog samples is investigated under irradiation with O+, O2+, C+, and CO2+ ions. The focus was put on oxygen ions and molecular ions that can be expected to escape the Martian atmosphere and cause sputtering of the surface of Phobos. In general, erosion rates are found to be smaller than previously calculated. Additionally, no significant differences in sputtering effects are observed for atomic versus molecular ions. The presented experimental studies support previous conclusions about the unique sputtering conditions on Phobos: in the Martian tail regions, where the planet shadows the solar wind, oxygen ions from the atmosphere of Mars dominate the erosion of the surface of Phobos. Key Points: Experiments with Phobos analogs were carried out to evaluate the sputtering by O+, C+, O2+, and CO2+ ions from the Martian atmosphereThe sputter yield from O ions is lower than previously assumed, and no yield increases due to molecular effects were observedPrevious predictions that planetary O ions will dominate sputtering in the Martian tail region are supported by the measurements presented [ABSTRACT FROM AUTHOR]

Atomically clean polycrystalline gold has been bombarded by slow cluster ions (N2)+n (n≤120), Ne+n (n≤100), and Cq+60,70 (q=1–4) at kinetic energies from the apparent electron emission thresholds up to 6 kV times the cluster charge (qe). The resulting electron yields have been derived from the corresponding electron emission statistics. Grossly different electron yields were found for different cluster species of about equal masses and velocities, which is attributed to different partitions of the initial cluster kinetic energy among (a) inelastic binary collision processes involving cluster constituents and surface atoms, and (b) intramolecular vibrational excitation in the cluster ions (where possible). We found emission threshold velocities of ∼1×104 m/s, which is a lower velocity than where emission was observed in most other studies previously conducted. For (N2)+n cluster ions, clear evidence for a nonlinear behavior (i.e., increasing electron emission per cluster constituent with increasing cluster size) has been found. [ABSTRACT FROM AUTHOR]

Presents a study which examined capillary discharge plasmas by developing a time-dependent, zero-dimensional collisional-radiative model. Description of the model; Result of the discharge current and discharge voltage; Calculations for lithium plasmas.

In tokamak plasmas with different main ion species, a change in confinement occurs, known as the isotope effect. Experiments comparing hydrogen (H), deuterium (D), and helium (4He) plasmas have been performed to identify processes that define the pedestal structure and evolution in between the crashes of edge localized modes (ELMs). The pedestal top electron densities and temperatures have been matched to compare the pedestal shape and stability. In the D and H discharges, the pedestal electron temperature profiles do not differ, whereas the density profile in H has shallower gradients. Furthermore, the heat flux across the pedestal in H is roughly a factor of two higher than in D. In 4He plasmas at similar stored energy, the pedestal top electron density is roughly a factor of 1.5 larger than in the references owing to the larger effective charge. The peeling-ballooning theory, which is independent of the main ion species mass, can sufficiently describe the pedestal stability in the hydrogenic plasmas. The inter-ELM pedestal evolution has the same sequence of recovery phases for all investigated species, giving evidence that similar mechanisms are acting in the pedestals. This is further supported by a similar evolution of the inter-ELM magnetic signature and the corresponding toroidal structure. [ABSTRACT FROM AUTHOR]

Modification of surface and bulk properties of solids by irradiation with ion beams is a widely used technique with many applications in material science. In this study, we show that nano-hillocks on CaF2 crystal surfaces can be formed by individual impact of medium energy (3 and 5 MeV) highly charged ions (Xe22+ to Xe30+) as well as swift (kinetic energies between 12 and 58 MeV) heavy xenon ions. For very slow highly charged ions the appearance of hillocks is known to be linked to a threshold in potential energy (Ep) while for swift heavy ions a minimum electronic energy loss per unit length (Se) is necessary. With our results we bridge the gap between these two extreme cases and demonstrate, that with increasing energy deposition via Se the Ep-threshold for hillock production can be lowered substantially. Surprisingly, both mechanisms of energy deposition in the target surface seem to contribute in an additive way, which can be visualized in a phase diagram. We show that the inelastic thermal spike model, originally developed to describe such material modifications for swift heavy ions, can be extended to the case where both kinetic and potential energies are deposited into the surface. [ABSTRACT FROM AUTHOR]

The lithium beam emission spectroscopy (Li-BES) is a powerful diagnostic to resolve the plasma edge density with high temporal and spatial resolution. The recent upgrades of the Li-BES at ASDEX Upgrade and the resulting gain in photon flux allow the plasma edge density to be determined with an advanced level of accuracy. Furthermore, electron density fluctuations are measured using Li-BES. The Li-BES capabilities and limitations to measure electron density profiles as well as density fluctuations are presented. It is well suited to characterize electron density turbulence in the scrape off layer (SOL) with decreasing sensitivity towards the plasma core. This is demonstrated by simulations as well as by comparisons with other diagnostics. The Li-BES is an appropriate tool to study transport phenomena in the SOL over a wide range of plasma parameters due to its robustness and routine usage. [ABSTRACT FROM AUTHOR]

Predictive-iterative modelling has been performed to investigate the role of convective and diffusive particle transport in the edge during the density build-up after the L-H transition. For the time-dependent modelling, the 1.5D radial transport code ASTRA has been used. The convective velocity, diffusion coefficient and the particle source profiles have been parameterized. Their parameters were varied until the best match of the modelling to the density measurements was found. The extensive parameter scans show that the density build-up can be reproduced by assuming only a diffusive edge transport barrier (ETB) with reduced diffusion coefficient at the edge with respect to the core values. Moreover, the replacement of the diffusive ETB by a strong inwards directed convective velocity at the edge (edge pinch) did not succeed in describing the data. This indicates that a diffusive ETB is required to explain the density build-up. However, the addition of an edge pinch to the diffusive ETB barrier slightly enhances the agreement between modelling and experiment. The best agreement was found with an edge diffusion coefficient of 0.031 m² s-1 and an edge convective velocity of -0.5 m s-1. Because of the large uncertainties in the source, it is not possible to pin down the exact value for the additional edge pinch. An upper limit for a possible edge convective velocity of -5 m s-1 was estimated. These findings could also be confirmed by analysing H-mode phases of a collisionality scan, in which the normalized collisionality ν* varied from 3.5 to 5.5 at the pedestal top. [ABSTRACT FROM AUTHOR]

The development of the electron density profile and its dependences after the L-H transition have been investigated. Only electron cyclotron resonance heated H-modes have been analysed to exclude core particle fuelling. While the density gradient in the edge transport barrier increases significantly after the L-H transition, the pedestal top temperature rises continuously with the applied heating power and shows no pronounced change at the transition. The H-mode density saturates at a level which correlates with the neutral gas density in the divertor prior to the L-H transition. Although the density build-up varies with the available deuterium inventory, the initial increase in the edge density gradient is similar. This has been observed independent of the L-mode plasma collisionality (ν* ≈ 2.8-5.5). The analysis of electron density and temperature profiles reveals that L-H and H-L transitions occur at similar pedestal top pressures, but the pedestal top densities are always higher at the time of the H-L back transition. [ABSTRACT FROM AUTHOR]

The introduction of gases like nitrogen or neon for cooling the edge region of magnetically confined fusion plasmas has triggered a renewed interest in state-selective cross sections necessary for plasma diagnostics by means of charge exchange recombination spectroscopy. To improve the quality of spectroscopic data analysis, charge exchange and ionization cross sections for N7+ + H(n = 1, 2) have been calculated using two different theoretical approaches, namely the atomic-orbital close-coupling method and the classical trajectory Monte Carlo method. Total and state-resolved charge exchange cross sections are presented in detail. In the second part, we compare two collision systems involving equally charged ions, C6+ and N6+ on atomic hydrogen. The analysis of the data leads to the conclusion that deviations between these two impurity ions are practically negligible. This finding is very helpful when calculating cross sections for collision systems with heavier not completely stripped impurity ions [ABSTRACT FROM AUTHOR]

The lithium beam diagnostic at ASDEX Upgrade routinely delivers electron density profiles in the plasma edge by lithium beam impact excitation spectroscopy. An accurate background subtraction requires a periodically chopped lithium beam. A new, improved chopping system was developed and installed. It involves a voltage modulation for the extractor electrode and the beam deflection plates. The modulation of the extractor electrode reduces the unused portion of lithium ions and improves the stability of the beam with respect to its position. Furthermore, the data indicate an extended emitter lifetime. The extractor chopping was also found to be insensitive to sparks. The deflection chopping experiments demonstrated beam chopping in the kilohertz range. The significantly higher modulation frequency of the deflection chopping improves background subtraction of fast transient events. It allows a more accurate density measurements in the scrape off layer during impurity injections and edge localized modes. [ABSTRACT FROM AUTHOR]

It has recently been demonstrated that slow (v < < 1 a.u.) highly charged ions (HCIs) are able to generate nano-sized hillocks on cleaved CaF2(1 1 1) surfaces. The aim of the present study was to explore whether surface nanostructures can also be formed on other target materials by the impact of slow HCIs. To this purpose, we have irradiated LiF(0 0 1), diamond-like carbon (DLC) and Au(1 1 1) with slow Xe HCIs (up to charge state 44+) from the Heidelberg electron beam ion trap. After irradiation, the crystals were investigated by scanning force microscopy. Nanometric hillocks protruding from the surface were found in the topographic images for the case of Xeq+ on LiF(0 0 1) for charge states q ≥ 28, but not for DLC and Au(1 1 1). [ABSTRACT FROM AUTHOR]

The energy loss of hydrogen atoms with energies of 400 eV and 1 keV is studied in coincidence with the number of emitted electrons during grazing scattering from atomically clean and flat KI(001) and LiF(001) surfaces. The energy loss spectra for specific numbers of emitted electrons are analyzed in terms of a binary interaction model based on the formation of transient negative ions via local capture of valence band electrons from anion sites. Based on computer simulations we derive for this interaction scenario probabilities for the production of surface excitons, for electron loss to the conduction band of KI, for emission of electrons, and for formation of negative hydrogen ions. The pronounced differences of data obtained for the two surfaces are attributed to the different electronic structures of KI and LiF. [ABSTRACT FROM AUTHOR]

A novel technique to identify small fluxes of mixed highly charged ion beams extracted from an electron beam ion trap is presented and practically demonstrated. The method exploits projectile charge state dependent potential emission of electrons as induced by ion impact on a metal surface to separate ions with identical or very similar mass-to-charge ratio. [ABSTRACT FROM AUTHOR]

Spontaneous (metastable) and surface-induced decay reactions for multiply charged fullerene ions, investigated recently in Innsbruck, are reviewed. Results discussed include the mechanisms and energetics of C2 evaporation and charge separation reactions, the secondary electron emission upon impact on gold surfaces, and surface-induced reactions of singly and multiply charged fullerene ions. [ABSTRACT FROM AUTHOR]

Describes a quartz-crystal microbalance technique for measuring total sputter yields in ion-surface collisions. Low noise and high frequency stability; Measurement of total sputter fields for impact of singly charged ions on LiF target films; Sensitivity limit.

Describes an innovative electron detector geometry for measuring electron multiplicities and absolute total electron yields from particle-induced electron emission. Application in coincidence measurements of slow singly and multiply charged ion-induced electron emission from a clean monocrystalline gold surface; Characteristic features and operation of the electron detector.

We demonstrate the application of Li-CXS (fast lithium-beam-activated charge exchange spectroscopy) for measuring spatially and temporally resolved impurity ion concentrations in the TEXTOR tokamak edge plasma. After briefly describing the method of Li-CXS and its capabilities, we present a model for attenuation and atomic state population of an injected Li beam due to collisional interactions with the background plasma particles, taking into account up to eight excited LiI states for considering stepwise excitation-ionization processes. Measured impurity radiation characteristics resulting from Li-activated CX of C ( q=5, 6) in ohmically heated TEXTOR plasmas are evaluated with the above model and lead to the corresponding impurity ion concentrations within the TEXTOR edge region. [ABSTRACT FROM AUTHOR]

Experimental cross sections for single electron capture and target atom resonance line emission in impact of singly charged ions (He, Ne, Ar, C, N, O) on respectively Li(2 s) and Na(3 s) are presented and compared with semiempirical calculations of the Demkov-Olson type. It is shown that such calculations can still be useful despite involvement of metastable primary ion admixtures and several final states. In addition, observed undulations in the impact energy dependence of electron capture - and target excitation cross sections are discussed. [ABSTRACT FROM AUTHOR]

Describes precise measurements of total electron yields for ion-induced electron emission from a clean polycrystalline gold surface under perpendicular impact of singly and multiply charged ions at impact energies from practically 0 up to 40 keV times primary ion charge. Determination of absolute total electron yield; Impact velocity.

We present a new technique for selective, highly sensitive, absolute detection of different multiply charged ion species with equal charge-to-mass ratios in mixed multicharged ion beams. This is achieved by exploiting the statistics of potential electron emission as induced by the ion beams on a clean metal surface. The applicability of the method is illustrated by way of different practical examples. [ABSTRACT FROM AUTHOR]

Plasma-wall interaction and impurity transport processes in the outermost region of magnetically confined hot plasmas (the so-called plasma edge) must be well understood for successful development of future thermonuclear fusion reactors. To this goal, sufficiently detailed edge plasma diagnostics are in great demand. By injecting a fast Li beam into the edge plasma region, a great number of information can be obtained with excellent space and time resolution. This so-called Li-beam plasma spectroscopy gives access not only to edge plasma density profiles from the collisionally excited Li atoms, but also to the impurity concentration and temperature profiles via line emission induced by electron capture from the injected Li atoms by the impurity ions. Full utilization of all capabilities requires a reliable data base for the atomic collision processes involving injected Li atoms and plasma constituents (i.e., electrons, hydrogen ions, and relevant impurities in their various charge states), since a precise modeling of Li beam attenuation and excited-state composition has to be made for evaluating desired plasma properties from the related spectroscopical measurements. The most recent methodical improvement permits a fully consistent determination of absolute edge plasma density profiles by measuring only relative LiI line emission profiles. This is of special interest for investigating rapid edge plasma density fluctuations in connection with, e.g., ELMs, L-H mode transition, turbulence or edge cooling by impurity injection. This paper describes the capabilities of Li-beam edge plasma spectroscopy by way of illustrative examples from measurements at the tokamak experiment TEXTOR. [ABSTRACT FROM AUTHOR]

With a novel combination of experimental approaches, ion-induced electron emission from clean polycrystalline gold bombarded with (1-5 keV/amu) H[sup +], H[sub 2, sup +], and H[sub 3, sup +] has been studied by measuring total electron yields, ejected-electron energy distributions, and, in particular, electron emission statistics (ES). Evaluation of ES included corrections for backscattering of electrons from the surface of the applied solid-state electron detector. By comparing ES for atomic and molecular ions of equal impact velocities, a negative molecular effect could be clearly demonstrated. This effect was further investigated by comparing measured ES for molecular ion impact with ES synthesized from measured ES for H[sup +] and H[sub 2, sup +] ion impact, respectively. The quality of approximating measured ES by Poisson and Polya statistical distributions was investigated in detail and found to be generally unsatisfactory. [ABSTRACT FROM AUTHOR]

Collisions of singly and multiply charged ions C[sub 60][sup z+] (z=1,2,3,4,5) with a hydrocarbon-covered stainless steel surface have been investigated; product ions of fragmentation and pickup reactions were determined as a function of the collision energy (100-500 eV) and the projectile charge z. All ions scattered off the surface are singly charged. The extent of fragmentation increases with the collision energy and the projectile charge. However, the increase of fragmentation with the charge of the projectile is less pronounced than expected from a full conversion of electronic energy, gained in the neutralization process, into internal energy of the ion. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A low-cost, single-stage 5 GHz electron cyclotron resonance (ECR) multieharged ion source (MCIS) has been constructed for various atomic collision experiments.. It features an axial magnetic field with a mirror ratio of up to five, and a magnetic hexapole field produced by a simple Nd-Fe-B permanent-magnet assembly. A disk probe axially mounted near the ECR resonance zone opposite to the ion extraction, and negatively biased with respect to the ECR plasma potential, permits reduction of the appropriate neutral feeding gas pressure by an Order of magnitude, resulting in greatly improved ion charge state distributions, as normally offered by two-stage ECR-MCIS only. We present performance data for multicharged ion production from Ar and N[sub 2], including measured ion current emittances. [ABSTRACT FROM AUTHOR]

Studies on electron capture in slow ion - atom/molecule collisions are presented in view to diagnostics and modelling of the tokamak edge plasma region. [ABSTRACT FROM AUTHOR]