Study Of Ion Transport Research Articles

An ion soft-landing apparatus for ion transport study with surface potential measurement.

An apparatus for explorations of ion transport in a medium and across an interface has been constructed. The ion soft-landing technique is used to deposit low-energy ions onto a pre-adsorbed medium layer on a metal substrate. The designed low-energy ion source can produce a mass-filtered ion beam with tens of nanoampere from solid sources such as bulk metals and salts. The kinetic energy of the ion beam can be lower than 1.0eV, enabling the ions to be soft-landed onto the medium at the surface. A Kelvin probe with a resolution of less than 32 mV is incorporated to measure the surface potential (SP) variation of the ion-landed sample to monitor the ion transport process in the medium. Temperature-programmed SP measurements on an Ag+-adsorbed ice film prepared on Pt(111) reveal that the temperature threshold for the Ag+-induced SP change of the ice film is about 110K. The apparatus performance demonstrates its potential in studies of ion transport and related phenomena at both macroscopic and microscopic levels.

From grass to yeast; functional insights from heterologous expression of LfHKT2;1 in ion regulation

Saccharomyces cervisceae mutants lacking the major potassium trasnporters trk1 and trk2 show hypersensitivity to aminoglycoside antibiotic hygromycin (hyg). This study demonstrates that expression of the inward K+ transporter LfHKT2;1 can suppress this hygromycin sensitivity in the trk1, trk2 double mutant strain. Growth complementation was performed on solid yeast peptone dextrose (YPD) media supplemented with hygromycin B. Both, wild type and trk1 trk2 yeast strains exhibited growth inhibition in the presence of hygromycin. However the potassium uptake-deficient trk1 trk2 strain (control) showed complete growth arrest when exposed to hygromycin, while expression of LfHKT2;1 resulted in growth recovery. Increased sodium concentrations caused cellular toxicity in the trk1 trk2 strain, which was exacerbated by the addition of hygromycin to the media. The hypersensitivity of trk1 trk2 mutant yeast cells expressing LfHKT2;1 to sodium suggested the presence of an additional sodium uptake system on the membrane, which was further confirmed by transient GFP expression assays. These results provide conclusive evidence that heterologous expression of LfHKT2;1 confers both sodium and K+ uptake capabilities in hygromycin supplemented YPD media, thereby rescuing the growth of K+ transport-deficient S. cerevisiae mutants. This highlights the potential of plant gene expression in yeast as a valuable tool for studying ion transport mechanisms and gene function under stress conditions.

In Situ Visualization of Ion Transport Processes in Aqueous Batteries.

Aqueous rechargeable batteries are regarded as one of the most reliable solutions for electrochemical energy storage, and ion (e.g., H+ or OH-) transport is essential for their electrochemical performance. However, modeling and numerical simulations often fall short of depicting the actual ion transport characteristics due to deviations in model assumptions from reality. Experimental methods, including laser interferometry, Raman, and nuclear magnetic resonance imaging, are limited by the complexity of the system and the restricted detection of ions, making it difficult to detect specific ions such as H+ and OH-. Herein, in situ visualization of ion transport is achieved by innovatively introducing laser scanning confocal microscopy. Taking neutral Zn-air batteries as an example and using a pH-sensitive probe, real-time dynamic pH changes associated with ion transport processes are observed during battery operation. The results show that after immersion in the zinc sulfate electrolyte, the pH near the Zn electrode changes significantly and pulsation occurs, which demonstrates the intense self-corrosion hydrogen evolution reaction and the periodic change in the reaction intensity. In contrast, the change in the pH of the galvanized electrode plate is weak, proving its significant corrosion inhibition effect. For the air electrode, the heterogeneity of ion transport during the discharging and charging process is presented. With an increase of the current density, the ion transport characteristics gradually evolve from diffusion dominance to convection-diffusion codominance, revealing the importance of convection in the ion transport process inside batteries. This method opens up a new approach of studying ion transport inside batteries, guiding the design for performance enhancement.

Transformer enables ion transport behavior evolution and conductivity regulation for solid electrolyte

Ab initio molecular dynamics (AIMD) is an important technique for studying ion transport within solid electrolyte and interface effects between electrode and electrolyte, which is particularly critical for the rational design of new energy materials. However, AIMD is limited by the high-cost density functional theory (DFT) solution process and is unable to reach the time scale of the entire dynamic simulation, resulting in time-consuming AIMD calculations and a considerable scarcity of AIMD-based conductor data. Here, we propose a sequence relational large model based on transformer (T-AIMD) to infer ion diffusion from mean square displacement sequence data and hybrid multi-source material descriptor. T-AIMD successfully learns the whole long-range atomic diffusion to predict the ionic conductivity (σ) of any ion in any crystal structure to find fast-ion conductors, thus reducing the cost of AIMD simulation by a factor of 100. Using T-AIMD, we built the largest database of mixed ion conductors, and the σ of representative solid electrolytes has been successfully validated in previous battery experiments. Further, the manufactured solid-state battery with the predicted promising electrolyte exhibits almost no obvious capacity decay after 50 cycles with a high initial specific capacity of 1270 mAh g−1, which is promising to help devices work in extreme environments while guaranteeing battery life. By speeding up the prediction time of AIMD, the proposed T-AIMD opens the door for scientists to explore the atomic and molecular behaviors of other molecules/materials on long time scales, and will ultimately benefit the exploration of other key scientific questions in the energy field.

Studying ion transport dynamics in electrochemical measurements of lateral flow assays

Lateral Flow Assays (LFAs) are among the most widely used biosensors. Conventional colorimetric LFAs yield binary, non-quantifiable results. Electrochemical LFAs (eLFAs) aim to overcome this limitation. However, the reported disadvantage of extreme sensitivity to experimental conditions poses a significant challenge in the development of new eLFAs. In this work, impedimetric measurements were performed to probe the impact of experimental factors such as electrolyte conductivity/ionic strength on the eLFA outcomes. The time-dependent evolution of non-Faradaic impedance measurements coupled with flow velocity computations were employed to investigate ion transport across different LFA configurations and buffer compositions. The analysis of the Péclet number, a characteristic dimensionless parameter of flow dynamics within the LFA, revealed the coexistence of diffusive and convective ionic transport regimes over the LFA operational time. In addition, our findings underscore the critical role of absorbent pad dead volume adjustments in governing the capacity to maintain sample flow within the membrane over extended durations. These electro-fluidics phenomena are essential considerations for conducting electrochemical measurements within LFAs. Overall, this study offers insights into key design parameters for the integration of electrochemistry into LFAs.

Highly selective ion transport by freestanding Zn-Imidazole complex intercalated graphene oxide membrane for enhanced blue energy harvesting

Generating electricity from seawater by utilizing nanofluidic structures is an appealing strategy for achieving zero-emission energy goals. A nanofluidic channel that is atomically small, tunable, and mechanically stable is the key to solving this problem. In this paper, for the first time, we report the construction of centimeter-sized freestanding zinc-imidazole complex (ZnIm) intercalated graphene oxide (GO) membrane (GO-ZnIm) having uniform 2D nanofluidic channels with interlayer spacing of 9 Å. The pristine GO membrane rapidly disintegrates in an aqueous medium due to membrane swelling; however, treatment with an aqueous zeolitic imidazole framework (ZIF-8) suspension, rendering ZnIm complex, provides long-term stability by restricting the excessive interlayer separation of GO sheets. From ion transport, diffusion, and variable load studies, it is observed that, besides stabilizing the GO membrane, intercalation of ZnIm significantly improves average cation selectivity (from 0.46 for GO to 0.74 for GO-ZnIm, measured up to 1000 concentration gradient) and experimental power density (from 1.7 Wm−2 for GO to 10.8 Wm−2 for GO-ZnIm, at 1000 concentration gradient). Moreover, the practical applicability of the GO-ZnIm membrane has also been investigated under artificial estuary conditions at ambient temperature, rendering an osmotic power density of 4.5 Wm−2, which is very close to the commercial benchmark of 5 Wm−2. A mechanically robust and flexible membrane made up of cost-effective components (GO and ZnIm), able to deliver an osmotic power density close to commercial benchmark at ambient temperature is the main highlight of the present GO-ZnIm membrane, which can be a promising candidate for applications such as separation, desalination, and blue energy harvesting.

An innovative perovskite oxide enabling improved efficiency for low-temperature ceramic electrochemical cells

In recent years, energy carriers for renewable sources and devices that convert chemical energy into electrical energy, such as solid oxide fuel cells (SOFCs) and solid oxide electrolysis cells (SOECs), have made hydrogen production economically viable and have numerous industrial uses. We have designed SrFe0.3TiO3 (SFT) materials to function as SOFC and H-SOEC electrolytes at low operational temperatures of 520–420 °C. The SFT (600 °C) shows a higher fuel cell power density of 650 mW/cm2 and a reasonable current density of 1.14 A/cm2 in fuel cell and electrolysis cell mode at 520 °C. The formation of the surface layer enables high ionic and Proton conduction due to a high number of oxygen vacancies, and the core–shell type interface enables easy and quick proton transportation restricted to the surface. Energy band alignment and distribution relaxation time (DRT) were also evaluated to study ion transport in SFT materials. These results open up advanced avenues for the design of high-performance, sophisticated proton-conducting electrolytes for ceramic electrochemical cells.

OrgaSegment: deep-learning based organoid segmentation to quantify CFTR dependent fluid secretion

Epithelial ion and fluid transport studies in patient-derived organoids (PDOs) are increasingly being used for preclinical studies, drug development and precision medicine applications. Epithelial fluid transport properties in PDOs can be measured through visual changes in organoid (lumen) size. Such organoid phenotypes have been highly instrumental for the studying of diseases, including cystic fibrosis (CF), which is characterized by genetic mutations of the CF transmembrane conductance regulator (CFTR) ion channel. Here we present OrgaSegment, a MASK-RCNN based deep-learning segmentation model allowing for the segmentation of individual intestinal PDO structures from bright-field images. OrgaSegment recognizes spherical structures in addition to the oddly-shaped organoids that are a hallmark of CF organoids and can be used in organoid swelling assays, including the new drug-induced swelling assay that we show here. OrgaSegment enabled easy quantification of organoid swelling and could discriminate between organoids with different CFTR mutations, as well as measure responses to CFTR modulating drugs. The easy-to-apply label-free segmentation tool can help to study CFTR-based fluid secretion and possibly other epithelial ion transport mechanisms in organoids.

Chitosan as a suitable host for sustainable plasticized nanocomposite sodium ion conducting polymer electrolyte in EDLC applications: Structural, ion transport and electrochemical studies

The challenge in front of EDLC device is their low energy density compared to their battery counter parts. In the current study, a green plasticized nanocomposite sodium ion conducting polymer blend electrolytes (PNSPBE) was developed by incorporating plasticized Chitosan (CS) blended with polyvinyl alcohol (PVA), doped with NaBr salt with various concentration of CaTiO3 nanoparticles. The most optimized PNSPBE film was subsequently utilized in an EDLC device to evaluate its effectiveness both as an electrolyte and a separator. Structural and morphological changes were assessed using XRD and SEM techniques. The PNSPBE film demonstrated a peak ionic conductivity of 9.76×10−5 S/cm, as determined through EIS analysis. The dielectric and AC studies provided further confirmation of structural modifications within the sample. Both TNM and LSV analyses affirmed the suitability of the prepared electrolyte for energy device applications, evidenced by its adequate ion transference number and an electrochemical potential window of 2.86 V. Electrochemical properties were assessed via CV and GCD techniques, confirming non-Faradaic ion storage, indicated by the rectangular CV pattern at low scan rates. The parameters associated with the designed EDLC device including specific capacitance, ESR, power density (1950 W/kg) and energy density (12.3 Wh/kg) were determined over 1000 cycles.

Reversal of the Parallel Drift Frequency in Anomalous Transport of Impurity Ions.

It is found that, in the studies of heavy ion transport with gyrokinetic simulations, the ion parallel drift frequency can reverse sign in velocity space when the amplitude variation of the electrostatic potential fluctuation is strong along the magnetic field line. As a result, the particle transport related to the parallel dynamics is strongly enhanced. It is noted that, while parallel gradient of the fluctuation amplitude can be instigated by a large magnetic shear or safety factor in a tokamak, the generic mechanism is independent of its cause, which suggests broader applications to kinetic plasma problems. Some relevant topics are briefly addressed in the end.

Probing and evaluating transmembrane chloride ion transport in double walled trifluorophenyl/phthalimide extended calix[4]pyrrole-based supramolecular receptors.

Therapeutic applications have sparked increased interest in the use of synthetic anion receptors for ion transport across lipid membranes. In this context, the construction of synthetic transmembrane transporters for the physiologically important chloride ion is currently of enormous interest. As a result, considerable effort is being devoted to the design and synthesis of artificial transmembrane chloride ion transporters. However, only inadequate progress has been made in developing macrocyclic chloride ion transporters using the fundamental principles of supramolecular chemistry, and hence this field entails fostering investigations. In this investigation, the synthesis of two new double walled trifluorophenyl/phthalimide extended calix[4]pyrrole (C4P) receptors (3 and 7) has been successfully reported. 1H-NMR titration and HRMS studies confirmed the 1 : 1 binding stoichiometry of the chloride ion with these receptors in the solution phase (only receptor 3b was studied by 1H-NMR). Regarding ion transport of 3b and 7, when studied in the HPTS-based vesicular system, 3b showed better activity with an EC50 value of 0.39 μM. The detailed ion transport studies on 3b have revealed that ion transport occurs through the Cl-/NO3- antiport mode.

Ion Transport in Plasticized Li1.5Al0.5Ge1.5(PO4)3 Based Electrolytes

The development of an efficient devices for energy storage, conversion, and transmission is one of the key priority areas today. At the center of these activities is the development of all-solid-state high-energy and high-power lithium-ion batteries.Our research is focused on the study of ion transport in a plasticized-by-ionic-liquid composite membrane formed by electrophoretic deposition (EPD). The EPD membrane comprises above 85% of high-ion-conductivity ceramic matrix Li1.5Al0.5Ge1.5(PO4)3 (LAGP) and less than 15% polyethyleneimine (PEI). The EPD rate and morphology of the membrane were characterized by SEM, TOFSIMS and DSC methods. 0.3M LiTFSI–PYR14TFSI was infused in the membrane to form a quasi-solid electrolyte. The complex, non-Debye dielectric response of the quasi-solid electrolyte, tested over the temperature and frequency ranges of (-140oC) to (+100oC) and 10-2 – 106 Hz, has been described in terms of several distributed relaxation processes separated by different frequency and temperature ranges. While at low temperatures, the main contribution is from LAGP, in the middle- and high-temperature regions, the superposition of a few non-Arrhenius processes is observed. Relaxation is perturbed by clear phase transition related to melting of the ionic liquid. Different scales of the ionic transport and corresponding relaxation of the apparent dipole moment in the materials are discussed.

Design of Chiral β-Double Helices from γ-Peptide Foldamers.

Chirality is ubiquitous in nature, and homochirality is manifested in many biomolecules. Although β-double helices are rare in peptides and proteins, they consist of alternating L- and D-amino acids. No peptide double helices with homochiral amino acids have been observed. Here, we report chiral β-double helices constructed from γ-peptides consisting of alternating achiral (E)-α,β-unsaturated 4,4-dimethyl γ-amino acids and chiral (E)-α,β-unsaturated γ-amino acids in both single crystals and in solution. The two independent strands of the same peptide intertwine to form a β-double helix structure, and it is stabilized by inter-strand hydrogen bonds. The peptides with chiral (E)-α,β-unsaturated γ-amino acids derived from α-L-amino acids adopt a (P)-β-double helix, whereas peptides consisting of (E)-α,β-unsaturated γ-amino acids derived from α-D-amino acids adopt an (M)-β-double helix conformation. The circular dichroism (CD) signature of the (P) and (M)-β-double helices and the stability of these peptides at higher temperatures were examined. Furthermore, ion transport studies suggested that these peptides transport ions across membranes. Even though the structural analogy suggests that these new β-double helices are structurally different from those of the α-peptide β-double helices, they retain ion transport activity. The results reported here may open new avenues in the design of functional foldamers.

Design of Chiral β‐Double Helices from γ‐Peptide Foldamers

AbstractChirality is ubiquitous in nature, and homochirality is manifested in many biomolecules. Although β‐double helices are rare in peptides and proteins, they consist of alternating L‐ and D‐amino acids. No peptide double helices with homochiral amino acids have been observed. Here, we report chiral β‐double helices constructed from γ‐peptides consisting of alternating achiral (E)‐α,β‐unsaturated 4,4‐dimethyl γ‐amino acids and chiral (E)‐α,β‐unsaturated γ‐amino acids in both single crystals and in solution. The two independent strands of the same peptide intertwine to form a β‐double helix structure, and it is stabilized by inter‐strand hydrogen bonds. The peptides with chiral (E)‐α,β‐unsaturated γ‐amino acids derived from α‐L‐amino acids adopt a (P)‐β‐double helix, whereas peptides consisting of (E)‐α,β‐unsaturated γ‐amino acids derived from α‐D‐amino acids adopt an (M)‐β‐double helix conformation. The circular dichroism (CD) signature of the (P) and (M)‐β‐double helices and the stability of these peptides at higher temperatures were examined. Furthermore, ion transport studies suggested that these peptides transport ions across membranes. Even though the structural analogy suggests that these new β‐double helices are structurally different from those of the α‐peptide β‐double helices, they retain ion transport activity. The results reported here may open new avenues in the design of functional foldamers.

A Numerical Study of Moisture and Ionic Transport in Unsaturated Concrete by Considering Multi-ions Coupling Effect

A Numerical Study of Moisture and Ionic Transport in Unsaturated Concrete by Considering Multi-ions Coupling Effect

Redox Polymer-Regulated Hysteresis in Ion Current Rectification through AAO Membranes and Single Nanopipettes

Nanopore technology has promising potential in fields such as high-density energy conversion, stochastic chemical sensing, logic operation and neuromorphic computing, separation and fundamental nanoelectrochemistry due to its rich ion transport features and easy fabrication. Understanding the ion transport dynamics at the solid-liquid interface is essential for further technological advancements. Ion current rectification (ICR) and its time-dependent hysteresis have been found to arise from the asymmetric nanointerfaces (geometry, together with surface charges in polarity and density). While various nanostructures can be fabricated and surface charges can be modified, active controls in ICR and hysteresis during transport applications are lacking. Here, we report actively controlled transport hysteresis in ion current rectification though PEDOT-modified single nanopipettes and anodic aluminum oxide (AAO) membranes. Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) provides high conductivity and chemical stability, low operating voltages, and enhanced performances in hydrophilicity, processability, and flexibility. The PEDOT:PSS aqueous dispersion is crosslinked inside a nanopipette or assembled onto one side of the AAO surface. Oxidation and reduction reversibly switch the PEDOT between the positive and neutral form, and thus modulate the space charge in nanopores or across the AAO membranes, correspondingly, the ion transport behaviors. The amplitude and polarity of ICR and the scale of hysteresis through a nanopore or AAO membrane have been altered by oxidizing/reducing the PEDOT substrate by adjusting the external electrical field. In contrast, the surface charge varying on pH, ionic strength, and electrolyte type is commonly adopted in ion transport studies but cannot be externally regulated in real-time. Interestingly, negative differential resistance (NDR) is also found in the PEDOT-modified nanopores in simple KCl systems without external pressure differential or concentration gradients. The NDR peak position and magnitude can be easily adjusted by controlling the redox states of the PEDOT fillings. Figure 1

Induced-charge membrane capacitive deionization enables high-efficient desalination with polarized porous electrodes

Exposure of a conducting porous material to an electric field in electrolytes induces an electric dipole, which results in capacitive charging of cations and anions at opposite poles. In this letter, we investigate a novel desalination method using this induced-charge capacitive deionization (ICCDI). To do this, we devise a microscale ICCDI platform that can visualize in situ ion concentrations, pH shifts, and fluid flows, and study ion transport dynamics and desalination performances compared to conventional CDI with unipolar / bipolar connections. Similar ion concentration and fluid flow characteristics were observed in Ohmic, limiting, and over-limiting regimes, but variations in desalination performance trends were noted based on the number of stacks. In a single cell, ICCDI generates a higher electric field at the opposite poles of porous electrodes than simple conducted electrodes in CDIs with unipolar/bipolar connections, leading to superior salt removal and/or lower ionic current at a given applied voltage. This marks a clear contrast from CDI with bipolar connection, which lacks any advantage over CDI with unipolar connection in a single cell. These metrics of ICCDI however deteriorated as the stack number increased, likely due to short-circuiting between the dipoles. As a result, ICCDI in current form shows higher desalination efficient than conventional CDIs with low stack numbers (< 6), so we offer the scale-up module by repeating 4-stack ICCDI units. Our study enhances comprehension of ion transport dynamics and desalination performance in ICCDI, and the results could aid in the development of ICCDI for energy/cost-efficient desalination.

Mechanical properties and pore network connectivity of sodium montmorillonite as predicted by a coarse-grained molecular model

The study of ionic transport through hydrated sodium montmorillonite (Na-MMT)—the main swelling component of bentonite—is of significant interest to better understand its ability to contain contaminants. From a macroscopic viewpoint, porosity and tortuosity can be viewed as scaling factors connecting diffusion coefficients in the clay material to free diffusion coefficients of ions in water. In this work, the mechanical properties, porosity and tortuosity of Na-MMT were calculated using a bottom-up approach. First, the constructed coarse-grained mesoscopic models of Na-MMT were fitted to all-atom molecular dynamics simulations. Thirty different models—each containing one thousand 120 Å-wide hexagonal Na-MMT platelets—were generated. The dry densities considered herein range from 0.8 to 1.3 g/cm3. Second, calculated the models' elastic constants were in excellent agreement with experimental values reported in the literature. Third, each system's porosity, pore size distribution and pore network were analysed. Fourth, the pore network information was used to create a 3D image of hydrated Na-MMT, and random walk simulations were employed to evaluate its tortuosity. Finally, the porosity and tortuosity values estimated using the models were compared to macroscopic experimental values describing tritium and iodide diffusion in Na-MMT dominant bentonite. The values obtained using the models were fairly consistent with experimental values reported in the literature.

Energy dissipative and positivity preserving schemes for large-convection ion transport with steric and solvation effects

Ion transport plays a crucial role in biophysical and electrochemical applications. While being modeled by the classical Poisson–Nernst–Planck (PNP) equations, many ionic features are ignored in the course-graining modeling of ionic interactions. In this work, we study ion transport by modified PNP equations including effects arising from steric interactions and the Born solvation, which both could cause strong convection. The modified NP equations are first rewritten in a gradient-flow reformulation that involves mobility and chemical potential terms. The mobility is then approximated by upwind fluxes with various flux limiters on the half-grid points, and the chemical potential terms are then implicitly approximated by central differencing. The resulting first-order in time scheme is proved to be energy dissipative unconditionally. Furthermore, the unconditional existence of positive numerical concentration is proved by making use of the singularity of the entropy term, which prevents the concentration from approaching zero. The flux with the Minmod or Osher limiter is reduced to a second-order upwind flux in the strong convective limit. Numerical tests are performed to confirm the expected order of accuracy and the properties of the developed scheme at discrete level. In addition, our numerical experiments demonstrate that the developed schemes with limiters can achieve higher accuracy than the Scharfetter-Gummel scheme and classical upwind scheme in tests with strong convection. Finally, the developed schemes are applied to numerically assess the effects of Coulombic interaction, steric interaction, and Born solvation on the rectifying transport of ions through nanopores.

Study of positive ion transport to the plasma electrode in giant RF negative ion sources

Negative ion sources are fundamental components of neutral beam injectors (NBI), one of the main heating systems for fusion reactors. SPIDER is the full-scale prototype negative ion source for ITER NBIs. It is hosted in Padua as part of the Neutral Beam Test Facility (NBTF). It aims to extract up to 330Am−2 of negative hydrogen ions from an inductively coupled plasma, generated inside 8 cylindrical drivers. The negative ion production is enhanced by caesium evaporation inside the source.In caesium-seeded negative ion sources, negative ions are produced close to the extraction apertures, and they are mainly generated by surface conversion of neutral atoms and positive ions impinging on the ion source walls, particularly on the plasma grid. The conversion yields depend on the energy distribution of these precursors, and so does the energy of those particles which are reflected as negative ions. The positive ion flow in the extraction region may also impact on the extraction probability of negative ions, via momentum transfer. Besides, in giant multi-driver RF sources such as SPIDER, a gradient of plasma potential is present in the expansion region Sartori et al. (2021), affecting the positive ion transport towards the caesiated plasma electrode and their energy.To approach this complex problem, a 3D test-particle Monte Carlo code for tracing plasma motion in SPIDER was developed. Positive ions species are generated in different positions within the plasma source volume and are tracked under the influence of electric and magnetic fields. Then, Monte Carlo collisions are used to simulate the interaction with predetermined backgrounds of plasma and neutrals, with profiles derived from experimental data. The particles are traced until they hit the ion source walls. Finally, the energy distribution of the different particle species impinging on the plasma grid (PG) are determined, and used to assess the generation and the energy distribution of the produced H−.