Energetic Ions Research Articles

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Investigating ripple pattern formation and damage profiles in Si and Ge induced by 100 keV Ar+ ion beam: a comparative study.

Desired modifications of surfaces at the nanoscale may be achieved using energetic ion beams. In the present work, a complete study of self-assembled ripple pattern fabrication on Si and Ge by 100 keV Ar+ ion beam bombardment is discussed. The irradiation was performed in the ion fluence range of ≈3 × 1017 to 9 × 1017 ions/cm2 and at an incident angle of θ ≈ 60° with respect to the surface normal. The investigation focuses on topographical studies of pattern formation using atomic force microscopy, and induced damage profiles inside Si and Ge by Rutherford backscattering spectrometry and transmission electron microscopy. The ripple wavelength was found to scale with ion fluence, and energetic ions created more defects inside Si as compared to that of Ge. Although earlier reports suggested that Ge is resistant to structural changes upon Ar+ ion irradiation, in the present case, a ripple pattern is observed on both Si and Ge. The irradiated Si and Ge targets clearly show visible damage peaks between channel numbers (1000-1100) for Si and (1500-1600) for Ge. The clustering of defects leads to a subsequent increase of the damage peak in irradiated samples (for an ion fluence of ≈9 × 1017 ions/cm2) compared to that in unirradiated samples.

Experimental study on the radiation-induced destruction of organic compounds on the surface of the Moon

Volatile organic molecules and a complex organic refractory material were detected on the Moon and on lunar samples. The Moon’s surface is exposed to a continuous flux of solar UV photons and fast ions, e.g. galactic cosmic rays (GCRs), solar wind (SW), and solar energetic particles (SEPs), that modify the physical and chemical properties of surface materials, thus challenging the survival of organic compounds. With this in mind, the aim of this work is to estimate the lifetime of organic compounds on the Moon’s surface under processing by energetic particles. We performed laboratory experiments to measure the destruction cross section of selected organic compounds, namely methane (CH4), formamide (NH2CHO), and an organic refractory residue, under simulated Moon conditions. Volatile species were deposited at low temperature (17 - 18 K) and irradiated with energetic ions (200 keV) in an ultra-high vacuum chamber. The organic refractory residue was produced after warming up of a CO:CH4 ice mixture irradiated with 200 keV H+ at 18 K. All the samples were analyzed in situ by infrared transmission spectroscopy. We found that destruction cross sections are strongly affected (up to one order of magnitude) by the dilution of a given organic in an inert matrix. Among the selected samples, organic refractory residues are the most resistant to radiation. We estimated the lifetime of organic compounds on the surface of the Moon by calculating the dose rate due to GCRs and SEPs at the Moon’s orbit and by using the experimental cross section values. Taking into account impact gardening, we also estimated the fraction of surviving organic material as a function of depth. Our results are compatible with the detection of CH4 in the LCROSS eject plume originating from layers deeper than about 0.7 m at the Moon’s South Pole and with the identification of complex organic material in lunar samples collected by Apollo 17 mission.

Sulfur Implantation into Water Ice with Propane: Implications for Organic Chemistry on the Surface of Europa

We performed experiments of implantation of energetic sulfur ions (105 keV) into 2:1 water:propane ices at 80 K and analyzed the resulting refractory organic matter with ultrahigh-resolution mass spectrometry. Our goal was to characterize the organic matter processed in the surface conditions of Europa, where it would receive a heavy flux of energetic particles, including sulfur ions, and determine whether organosulfurs could be formed in these conditions, using the simplest alkane that can exist in solid form on Europa’s surface. We find that the produced organic matter contains a large variety of both aliphatic and aromatic compounds (several thousand unique formulae), including polycyclic aromatic hydrocarbons (PAHs), with masses up to 900 amu. A large number of aromatic hydrocarbons is found along with oxygenated, mostly aliphatic, compounds. Organosulfurs are found in both CHS and CHOS form, demonstrating they can be formed from any organic compound through sulfur implantation. These organosulfurs’ properties (aromaticity, mass) appear similar to the rest of the organic matter, albeit their low quantity does not allow for a thorough comparison. Our results have implications for the type of refractory organic matter that could be observed by the JUICE and Europa Clipper space missions and how the surface of Europa could generate complex organics, including PAHs and organosulfurs, that could then enrich the subsurface ocean. In particular, they indicate that a large diversity of organic matter, including organosulfurs, can be formed from simple precursors in a geologically short time frame under the ion flux that reaches Europa.

Comparison between conventional Si and new generation of SiC detector for high proton energy spectrometry

A SiC Schottky diode and a Si surface barrier detector have been compared during Rutherford backscattering spectrometry (RBS) using 2–3 MeV proton beams. Both detectors are suited to detect high energetic ions with high-energy resolution for spectroscopic analysis. The correlations between the detector parameters and the surface passivating layers, ion energy and current dependence, ion penetration depth, detection efficiency and energy resolution, are outlined. Comparative RBS analysis performed using SiC and Si detectors has been investigated to highlight the advantages and disadvantages of the use of SiC with respect to the traditional Si junction detector. RBS spectrometry has been carried out using projectiles of proton incident on different targets to analyse their composition and thickness by the detection of the backscattered ions revealed by Si and SiC detectors.

Hollow cathode discharge instability onset in electric thrusters

Hollow cathodes are an integral part of ion, and Hall thrusters are used for electric propulsion in deep space missions and in commercial communications satellites. Hollow cathodes are known to operate in a quiescent “spot mode” and in a noisy “plume mode” in which plasma instabilities generate erosive energetic ions. The onset of the plume mode in hollow cathodes has been defined historically as when the keeper voltage oscillation values exceed 5 Vpp (peak-to-peak). Using a LaB6 hollow cathode in a vacuum chamber setup that simulates operation in ion and Hall thrusters, a set of emissive and Langmuir probes have been used to investigate the plasma properties associated with plume mode onset as a function of discharge current and gas flow rate. We find that the plume mode onset occurs at even less than 2 Vpp of the keeper voltage for the 5–75 A hollow cathode investigated here and starts at higher gas flow rates than expected from the traditional 5 Vpp metric used by those in the field. Mode competition and coupling between three different instabilities observed in the near-cathode plume affect the overall plasma oscillation levels that are correlated to energetic ion production. We find that the plasma oscillation levels measured by in situ plasma diagnostics are more indicative of the presence of oscillations and the generation of energetic ions than indirect keeper voltage measurements.

Effects of multi-dimensionality and energy exchange on electrostatic current-driven plasma instabilities and turbulence

Large-amplitude current-driven plasma instabilities, which can transition to the Buneman instability, were observed in one-dimensional simulations to generate high-energy back-streaming ions. We investigate the saturation of multi-dimensional plasma instabilities and its effects on energetic ion formation. Such ions directly impact spacecraft thruster lifetimes and are associated with magnetic reconnection and cosmic ray inception. An Eulerian Vlasov–Poisson solver employing the grid-based direct kinetic method is used to study the growth and saturation of 2D2V collisionless, electrostatic current-driven instabilities spanning two dimensions each in the configuration (D) and velocity (V) spaces supporting ion and electron phase-space transport. Four stages characterise the electric potential evolution in such instabilities: linear modal growth, harmonic growth, accelerated growth via quasi-linear mechanisms alongside nonlinear fill-in and saturated turbulence. Its transition and isotropisation process bears considerable similarities to the development of hydrodynamic turbulence. While a tendency to isotropy is observed in the plasma waves, followed by electron and then ion phase spaces after several ion-acoustic periods, the formation of energetic back-streaming ions is more limited in the 2D2V than in the 1D1V simulations. Plasma waves formed by two-dimensional electrostatic kinetic instabilities can propagate in the direction perpendicular to the net electron drift. Thus, large-amplitude multi-dimensional waves generate high-energy transverse-streaming ions and eventually limit energetic backward-streaming ions along the longitudinal direction. The multi-dimensional study sheds light on interactions between longitudinal and transverse electrostatic plasma instabilities, as well as fundamental characteristics of the inception and sustenance of unmagnetised plasma turbulence.

Large-scale kinetic simulations of colliding plasmas within a hohlraum of indirect-drive inertial confinement fusion.

The National Ignition Facility has recently achieved successful burning plasma and ignition using the inertial confinement fusion (ICF) approach. However, there are still many fundamental physics phenomena that are not well understood, including the kinetic processes in the hohlraum. Shan etal. [Phys. Rev. Lett. 120, 195001 (2018)0031-900710.1103/PhysRevLett.120.195001] utilized the energy spectra of neutrons to investigate the kinetic colliding plasma in a hohlraum of indirect drive ICF. However, due to the typical large spatial-temporal scales, this experiment could not be well simulated by using available codes at that time. Utilizing our advanced high-order implicit PIC code, LAPINS, we were able to successfully reproduce the experiment on a large scale of both spatial and temporal dimensions, in which the original computational scale was increased by approximately seven to eight orders of magnitude. Not only is the validity of the explanation of the experiment confirmed by our simulations, i.e., the abnormally large width of neutron spectra comes from beam-target nuclear fusions, but also a different physical insight into the source of energetic deuterium ions is provided. The acceleration of deuterium ions can be categorized into two components: one is propelled by a sheath electric field created by the charge separation at the onset, while the other is a result of the reflection of the potential of the shock wave. The robustness of the acceleration mechanism is analyzed with varying initial conditions, e.g., temperatures, drifting velocity, and ion components. This paper might serve as a reference for benchmark simulations of upcoming simulation codes and may be relevant for future research on mixtures and entropy increments at plasma interfaces.

High-Harmonic Generation Spectroscopy of Gas-Phase Bromoform.

High-Harmonic Generation (HHG) spectra of randomly aligned bromoform (CHBr3) molecules have been experimentally measured and theoretically simulated at various laser pulse intensities. From the experiments, we obtained a significant number of harmonics that goes beyond the cutoff limit predicted by the three-step model (3SM) with ionization from HOMO. To interpret the experiment, we resorted to real-time time-dependent configuration interaction with single excitations. We found that electronic bound states provide an appreciable contribution to the harmonics. More in detail, we analyzed the electron dynamics by decomposing the HHG signal in terms of single molecular-orbital contributions, to explain the appearance of harmonics around 20-30 eV beyond the expected cutoff due to HOMO. HHG spectra can be therefore explained by considering the contribution at high energy of HOMO-6 and HOMO-9, thus indicating a complex multiple-orbital strong-field dynamics. However, even though the presence of the bromoform cation should be not enough to produce such a signal, we could not exclude a priori that the origin of harmonics in the H29-H45 to be due to the cation, which has more energetic ionization channels.

The Energetic Oxygen Ion Beams in the Martian Magnetotail Current Sheets: Hints From the Comparisons Between Two Types of Current Sheets

AbstractUsing data from the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission, we explore the plasma properties of Martian magnetotail current sheets (CS), to further understand the solar wind interaction with Mars and ion escape. There are some CS exhibit energetic oxygen ions that show narrow beam structures in the energy spectrum, which primarily occurs in the hemisphere where the solar wind electric field (Esw) is directed away from the planet. On average, these CS have a higher escaping flux than that of the CS without energetic oxygen ion beams, suggesting different roles in ion escape. The CS with energetic oxygen ion beams exhibits different proton and electron properties to the CS without energetic oxygen ion beams, indicating their different origins. Our analysis suggests that the CS with energetic oxygen ion beams may result from the interaction between the penetrated solar wind and localized oxygen ion plumes.

Wave Generation by Flare-accelerated Ions and Implications for 3He Acceleration

The waves generated by high-energy proton and alpha particles streaming from solar flares into regions of colder plasma are explored using particle-in-cell simulations. Initial distribution functions for the protons and alphas consist of two populations: an energetic, streaming population represented by an anisotropic (T ∥ > T ⊥), one-sided kappa function and a cold, Maxwellian background population. The anisotropies and nonzero heat fluxes of these distributions destabilize oblique waves with a range of frequencies below the proton cyclotron frequency. These waves scatter particles out of the tails of the initial distributions along constant-energy surfaces in the wave frame. Overlap of the nonlinear resonance widths allows particles to scatter into near-isotropic distributions by the end of the simulations. The dynamics of 3He are explored using test particles. Their temperatures can increase by a factor of nearly 20. Propagation of such waves into regions above and below the flare site can lead to heating and transport of 3He into the flare acceleration region. The amount of heated 3He that will be driven into the flare site is proportional to the wave energy. Using values from our simulations, we show that the abundance of 3He driven into the acceleration region should approach that of 4He in the corona. Therefore, waves driven by energetic ions produced in flares are a strong candidate to drive the enhancements of 3He observed in impulsive flares.

Modeling Ion Acceleration and Transport in Corotating Interaction Regions: The Mass-to-charge Ratio Dependence of the Particle Spectrum

We investigate the role of perpendicular diffusion in shaping the energetic ion spectrum in corotating interaction regions (CIRs), focusing on its mass-to-charge (A/Q) ratio dependence. We simulate a synthetic CIR using the EUropean Heliospheric FORecasting Information Asset and model the subsequent ion acceleration and transport by solving the focused transport equation incorporating both parallel and perpendicular diffusion. Our results reveal distinct differences in ion spectra between scenarios with and without perpendicular diffusion. In the absence of perpendicular diffusion, ion spectra near CIRs show a strong (A/Q) ϵ dependence with ϵ depending on the turbulence spectral index, agreeing with theoretical predictions. In contrast, the incorporation of perpendicular diffusion, characterized by a weak A/Q dependence, leads to similar spectra for different ion species. This qualitatively agrees with observations of energetic particles in CIRs.

Assessing trajectory-dependent electronic energy loss of keV ions by a binary collision approximation code

The inelastic energy deposition of energetic ions is a decisive quantity for numerous industrial-scale applications, such as sputtering and ion implantation, yet the underlying physics being governed by dynamic many-particle processes is commonly only qualitatively understood. Recently, transmission experiments on single-crystalline targets (Phys. Rev. Lett. 124, 096601 & Phys. Rev. A 102, 062803) revealed a complex energy scaling of the inelastic energy loss of low-energy ions heavier than protons along different trajectories. We use a Monte Carlo like binary collision approximation code equipped with an impact-parameter-dependent modeling of the inelastic energy losses to assess the role of local contributions to electronic excitations in these cases. We compare angular intensity distributions of calculated trajectories with experimental results for 50-keV 4He and 100-keV 29Si ions transmitted in a time-of-flight setup through single-crystalline silicon (001) foils with nominal thicknesses of 200 and 50 nm, respectively. In these calculations, we employ different models of electronic energy loss, i.e., local and nonlocal forms for light and heavy projectiles. We find that the vast number of projectiles are eventually channeled along their trajectories, regardless of the alignment of the crystal with respect to the incident beam. It is, however, only when local electronic energy loss is considered that the simulated two-dimensional maps and energy distributions show excellent agreement with the experimental results, where channeling leads to significantly reduced stopping, especially for heavier projectiles. We demonstrate the relevance of these effects for ion implantations by assessing the nonlinear and nonmonotonic scaling of the ion range with the thickness of a random surface layer. Published by the American Physical Society 2024

Modeling and experimental comparison of pulsed-DC driven low-pressure plasma discharge in a metal tube

High-voltage pulsed-DC can be used to deposit films on the inner surfaces of tubes and pipes. However, the characteristics of the plasma discharge in the tubes and mechanisms of film deposition are not well understood. In this study, a discharge is formed in a metal tube inserted with a coaxial anode by microsecond (μs) pulsed power to explore the influence of the pulse parameters on the plasma characteristics, including the temporal and spatial evolution near the tube walls experimentally and by simulation. The discharge waveform is monitored by a voltage-current probe to analyze the impact of the electrical characteristics on the plasma. The plasma properties are diagnosed by a Langmuir probe and numerically calculated by the fluid model. The source voltage and current jointly influence the plasma density and electron temperature, and secondary electron emission by energetic ion bombardment affects not only the distribution of electron density measured by the probe, but also the temporal distribution during the pulse-on and pulse-off time. The electron temperature varies conversely with the density from the plasma zone to the cathode suggesting the typical glow discharge in the pulsed-DC tube. Secondary electron emission is created at a higher discharge frequency, and a sustained plasma between pulse cycles appears to be produced at a higher frequency. The results impart information about the pulsed-DC driven plasma discharge at low pressure as well as the role energetic ions play on the cathode and elucidate the mechanisms of plasma deposition on the interior tube wall.

Observation of resonant tearing mode induced by energetic-ion redistribution due to sawtooth collapse in HL-2A NBI plasmas

Recent observations on the HL-2A tokamak give new experimental evidence of resonant tearing modes (r-TMs) caused by the redistribution of energetic ions (EIs) due to sawtooth collapses in neutral beam injection plasmas. The m/n=2/1 (m and n are the poloidal and toroidal mode numbers) r-TMs with frequencies chirping down rapidly are found after strong bursts of fishbone modes and closely followed strong sawtooth collapses. The frequencies of fishbone modes and r-TMs chirp down from 10 to 7 kHz and 5 to 2 kHz rapidly, higher and lower than the 4–6 kHz existing weak resistive TMs. The fishbone modes propagate in ion diamagnetic drift directions in poloidal. In contrast, r-TMs propagate in the electron diamagnetic drift direction, though r-TMs are excited by EIs. It is suggested that counter-passing EIs, which originated from redistribution of EIs due to fishbone modes and combined with sawtooth collapses, excite r-TMs. Simulation results from the M3D-K code reveal that the counter-passing EIs play an important role in the excitation of r-TMs. The results can help broaden understanding of the interaction mechanisms between energetic particles and TMs, and open up a new perspective on the excitation mechanism of r-TMs.

Nonlinear dynamics of multiple Alfvén modes driven by trapped energetic ions in tokamaks: A triplet paradigm

Non-linear dynamics of multiple infernal Alfvén eigenmodes—a subset of global Alfvén eigenmodes in tokamak plasmas with extended low-shear central core [Marchenko et al., Phys. Plasmas 16, 092502 (2009)]—is studied. The analysis is carried out for a mode triplet with toroidal mode-numbers n=1, 2, 3. It was assumed that the n = 1 mode was linearly unstable due to precession resonance with trapped fast ions, whereas the other modes were linearly damped. The modes were coupled due to a non-linearity in a bounce-averaged drift kinetic equation for the distribution function of fast ions. Nonlinear equations for the mode amplitudes and phases are derived and solved numerically. It is found that the temporal evolution of the amplitudes and the phase (responsible for the frequency chirping) of the modes exhibit Hopf bifurcations to stable limit cycles. This can explain a synchronous cyclic destabilization of multiple modes in Alfvén avalanches (sudden growth of amplitudes of the mode cluster with different n and approximately equal frequency spacing) in NSTX and bursting modes in MAST—events, which resulted in enhanced loss of fast ions.

Constraining the Influence of Callisto's Perturbed Electromagnetic Environment on Energetic Particle Observations

AbstractThis study focuses on constraining the role that Callisto's perturbed electromagnetic environment had on energetic charged particle signatures observed during the Galileo mission. To do so, we compare data from the Energetic Particle Detector (EPD) obtained during four close encounters of the moon with a model framework that combines hybrid simulations for low‐energy plasma and test‐particle tracing simulations for high‐energy particles. By comparing model results for energetic particle dynamics in both uniform and perturbed electromagnetic fields, we systematically disentangle the role that geometric effects (i.e., absorption of particles by Callisto's solid surface) have on observed energetic particle signatures compared to those associated with Callisto's perturbed electromagnetic environment (generated by the moon's induced magnetic field and plasma interaction currents). We show that observed flux drop‐outs in the energetic ion pitch angle distributions (PADs) are largely driven by their absorption by Callisto's surface: their large gyroradii exceed the size of the moon, facilitating their impact onto the icy surface and preventing their detection by EPD. However, features observed in the energetic electron PADs can only be explained with an accurate representation of the moon's perturbed environment, since electrons closely follow the orientation of the electromagnetic fields. Our findings therefore illustrate the key role that the moon's induced field and magnetospheric plasma interaction have on the dynamics of energetic electrons, emphasizing the importance of accurately modeling Callisto's locally perturbed electromagnetic environment when attempting to interpret data from past and future encounters, including those anticipated from the upcoming JUICE mission.

Long-Lived Recurrent Fluxes of Energetic Ions from Coronal Holes on the Sun

Long-Lived Recurrent Fluxes of Energetic Ions from Coronal Holes on the Sun

100 MeV protons from nanostructured hemispherical target using PIC simulations

The improvement of laser-driven proton energy with the use of nano-structured hemispherical targets of 100 nm thickness over conventional flat foil has been reported in this work. The curvature of the target is found to result in focussed particle density at the center of the hemispherical target followed by emergence of energetic ions due to combined action of sheath electric field and ambipolar expansion. The presence of nano-rods on the curved hemispherical target further increases the laser energy absorption by the electrons, thus resulting in increase in the maximum proton energy. Use of hemispherical target embedded with nanorods is possibly reported here for the first time that may generate protons with energy 92 MeV by using linearly polarised laser of intensity 1021 W cm−2 and pulse duration of 30 fs. At this laser intensity, the energy gain by the protons is much higher compared to the conventional flat foil targets. The maximum proton energy can be increased further to 103 MeV by using truncated hemispherical target of similar parameter.

INVESTIGATION OF PHOTOVOLTAIC POTENTIALS OF A SILVER IMPLANTED DIAMOND-LIKE CARBON THIN FILM

This paper investigated the optical response of silver implanted carbon-based thin films (deposited on quartz substrates) due to varying fluence of energetic Ag ions in the range 2.5 - 3.4 x 1016 ions/cm2. Raman spectroscopy was used to observe the microstructural specifics of the Ag:a-C composites. Atomic force microscopy (AFM) revealed significant increase in particle grain size and surface roughness of the films at varying fluences. Optical absorption spectra showed that the Surface Plasmon Resonance (SPR) of pristine Ag occurs at visible wavelength of about 428 nm but exhibited a blue shifting (~ 32 nm) in the implanted films. The blue shift in plasmonic wavelength occurs due to the fluence-induced increase in grain size and density of the Ag particles as confirmed by AFM. Optical band gap energy () and Urbach parameter () of the pristine carbon film increased, with fluence, from 2.89 eV to 1.60 eV and 3.60 eV to 4.22 eV respectively. The observed optically active parameters strongly indicate that the composites would make good candidates for photon retention towards the enhancement of solar cells’ efficiency.