Tens Of eV Research Articles

Electron Energization by Ion Density Enhancement in the Martian Magnetotail—MAVEN Observations

It has been long observed at Mars that electron fluxes are enhanced during the tail current sheet crossings, of which the cause is not well understood. We use a novel approach to reveal one of the electron energization mechanisms with observations from the Mars Atmospheric and Volatile EvolutioN (MAVEN) mission. We find the field-aligned potential, derived from comparing electron distribution functions, to be approximately linearly correlated with the logarithmic values of the local total ion density. This is the expected behavior of an ambipolar electrostatic potential. The large amplitude of potential (tens to hundreds of V) is a result of both a significant density gradient (1 order of magnitude) and the high electron temperature (tens of eV) in the tail. Such a mechanism is not limited to ion density enhancements at current sheet crossings but can be present anywhere that large ion density gradients and hot electrons are present.

Reimei Satellite Observations of Alfvénic Interaction Modulating Inverted‐V Electrons and Filamentary Auroral Forms at the Poleward Edge of a Discrete Arc

AbstractWe present an event based on Reimei satellite observations in the low‐altitude midnight auroral region, showing that intense and clear energy‐dispersed electron precipitations, repetitively generated by field‐aligned accelerations due to dispersive Alfvén waves, were modulating inverted‐V electrons. These Alfvénic electrons had peak energies equal to or slightly larger than those of the inverted‐Vs and were associated with the filamentary auroral forms rapidly streaming at the poleward edge of a broad discrete arc. This arc was caused by the inverted‐V accompanied by ion depletions produced by quasi‐electrostatic parallel potential drop. Assuming instantaneous electron accelerations over a wide energy range in a single location and a simple time‐of‐flight effect for the energy‐time dispersions, the Alfvénic source distances were estimated 1,500 ± 500 km above the satellite altitude of ∼676 km, a lower bound since the interaction locations are realistically distributed in altitudinally extended regions. The electron characteristics in detailed energy‐pitch angle distributions obtained at high time resolution can be categorized into: (a) original inverted‐V fluxes energized by quasi‐electrostatic upward electric field, (b) accelerated and decelerated/reduced inverted‐V fluxes, (c) field‐aligned energy‐dispersed precipitations accelerated by dispersive Alfvén waves, and (d) upwelling secondary components effectively produced by the field‐aligned precipitations particularly at energies of a few tens of eV. This event is useful to reveal the interactions between the inverted‐V and Alfvénic electrons and their related ionospheric effects in the magnetosphere‐ionosphere coupling processes. The detailed energy‐pitch angle distributions presented here provide constraints for models of these interactions and processes.

Simulation on the hollow cathode discharge in hydrogen

A rectangular hollow cathode discharge (HCD) in hydrogen with a pressure of 2 Torr is simulated using a 2-D fluid model. The potential, electric field, particle density, and average electron temperature are calculated. The discharge space consists of the cathode sheath region near the cathode electrode and the negative glow (NG) region in the central region of the discharge cell. A high electric field of thousands of V/cm and a low electric field of tens of V/cm appear in the cathode sheath region and NG region, respectively. The average electron temperature in the cathode sheath region is tens of eV, which is significantly higher than that in the NG region. Electrons and H3 + are the main negative particles and positive ions, whose peaks appear in the NG region, and the peak magnitude is on the order of 1010 cm−3. H atom is the highest-density neutral particle other than H2 with a peak density of 1013 cm−3. The reaction kinetics of the generation and consumption of different particles are explored. The results show that each reaction generates certain particles while consuming other particles, ultimately achieving a dynamic equilibrium in the density of various particles. The electrons mainly originate from the ground state ionization between electron and H2 (e+H2 → e+H2 ++e) and are consumed by the dissociative attachment (e+H2 → H−+H). The charge transfer collision reaction (H2 ++H2 → H3 ++H) is the only reaction that produces H3 + ions. Different reactions to the consumption of H3 + ions do not differ significantly. The generation and consumption of H mainly originate from the electron collision dissociation reaction (e+H2 → e+H+H) and the ionization reaction (e+H→H++2e).

A carbon nanotube based ion source for planetary space mass spectrometry.

Ion sources are used in mass and energy spectrometry to ionize the neutral particles entering the instrument. The most classical technique used in planetary exploration is hot filaments emitting electrons with few tens of eV and impacting the neutral particles. The main limitations of such emitters are power consumption and outgassing due to heating of their local environment. Here, we built, tested, and demonstrated the advantages of using carbon nanotubes to replace hot filaments. Such emitters are based on a cold approach, use a limited amount of power, and achieve essentially the same efficiency as the hot filament-based source of ionization.

Observation of Non‐Resonance Interactions Between Cold Protons and EMIC Waves of Different Polarizations in the Inner Magnetosphere

AbstractUsing the high‐quality measurements of plasma by the Magnetospheric Multiscale (MMS) spacecraft, we investigate the wave‐particle interaction between cold protons and Electromagnetic ion cyclotron (EMIC) waves of different polarizations in the inner magnetosphere. Both the left‐hand and right‐hand polarized EMIC waves can interact with cold protons via non‐resonance interaction, and energize the cold protons (∼eV) up to suprathermal energies (∼tens of eV), resulting in a series of bridge‐like arcs in the ion energy spectrogram. Cold protons experience different types of phase bunching in left‐hand and right‐hand polarized EMIC waves. However, the relative angles between the velocities of bunched protons and wave magnetic or electric fields are independent of the polarizations of EMIC waves. Thus, the energy transfer process is not affected by the polarization of EMIC waves. The observations indicate that EMIC waves can affect the magnetospheric particle dynamics by energizing the cold protons.

Imaging low-energy positron beams in real-time with unprecedented resolution

Particle beams focused to micrometer-sized spots play a crucial role in forefront research using low-energy positrons. Their expedient and wide application, however, requires highly-resolved, fast beam diagnostics. We have developed two different methods to modify a commercial imaging sensor to make it sensitive to low-energy positrons. The first method consists in removing the micro-lens array and Bayer filter from the sensor surface and depositing a phosphor layer in their place. This procedure results in a detector capable of imaging positron beams with energies down to a few tens of eV, or an intensity as low as 35e+/s/mm2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${35}\\,{\\hbox {e}^+/\\hbox {s/mm}^{2}}$$\\end{document} when the beam energy exceeds 10 keV\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\hbox {keV}}$$\\end{document}. The second approach omits the phosphor deposition; with the resulting device we succeeded in detecting single positrons with energies upwards of 6keV\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${6}\\,{\\hbox {keV}}$$\\end{document} and efficiency up to 93%. The achieved spatial resolution of 0.97 μm\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\upmu \\hbox {m}$$\\end{document} is unprecedented for real-time positron detectors.

Proton acceleration from TiH2 target plasma produced by different pulse laser intensity

AbstractThe laser irradiation of TiH2 targets has been investigated to measure the proton energy transferred by hot non‐equilibrium plasmas in vacuum. The proton and titanium emission have been monitored by time‐of‐flight measurements to evaluate their maximum ion energy and dependence on the laser intensity. Backward and forward plasma have been generated in the range 1010–1016 W/cm2 intensity using ns and sub‐ns laser shots. Proton energy has been measured by tens eV up to about 4 MeV. The interest in proton beams generated by laser‐plasma is presented and discussed.

Study of experimental method for warm dense matter ionization distribution based on x-ray fluorescence spectroscopy

Warm dense matter (WDM), a state of matter which lies at the frontiers between condensed matter and plasma, is one of the main research objects of high energy density physics (HEDP). Compared to the isolated atom, the electron structure of WDM will change because of the influence of density and temperature effect. Both the accurate theoretical represent and the accurate experimental study of WDM electron structure are challenging, as it is strongly coupled and partially degenerated. In this paper, an experimental method for studying the ionization distribution of warm dense matter based on x-ray fluorescence spectroscopy is developed. In the experiment, warm dense titanium with several tens eV and near solid density is created by a simultaneous drive from high energy xray heating and shock compression in a special designed hohlraum. Then, using the characteristic line spectrum emitted by the laser irradiation on pump material (Vanadium) as pump source, the titanium emits fluorescence. The x-ray fluorescence spectroscopy of titanium with different states (cold sample, 1.8-4.5 g/<i>cm</i><sup>3</sup> and 1-25 eV) is diagnosed by changing the experimental strategy. The experimental results indicate that the line profiles of <i>K<sub>α</sub></i> and <i>K<sub>β</sub></i> fluorescence spectrum of the heated sample change obviously relative to that of the cold sample. Associating a theoretical calculation from two-step Hartree-Fock-Slater (TSHFS) method, the reason for the variation of the line profile is the change of ionization distribution mainly caused by temperature rise. The future work will focus on optimizing the experimental method of x-ray fluorescence spectroscopy, such as improving the spectrum resolution, characterizing the temperature and density experimentally, obtaining a set of ionization distribution data, and then study the influence of dense environment on electronic structure.

Impact of the Lorentz force on electron track structure and early DNA damage yields in magnetic resonance-guided radiotherapy

Magnetic resonance-guided radiotherapy (MRgRT) has been developed and installed in recent decades for external radiotherapy in several clinical facilities. Lorentz forces modulate dose distribution by charged particles in MRgRT; however, the impact of Lorentz forces on low-energy electron track structure and early DNA damage induction remain unclear. In this study, we estimated features of electron track structure and biological effects in a static magnetic field (SMF) using a general-purpose Monte Carlo code, particle and heavy ion transport code system (PHITS) that enables us to simulate low-energy electrons down to 1 meV by track-structure mode. The macroscopic dose distributions by electrons above approximately 300 keV initial energy in liquid water are changed by both perpendicular and parallel SMFs against the incident direction, indicating that the Lorentz force plays an important role in calculating dose within tumours. Meanwhile, DNA damage estimation based on the spatial patterns of atomic interactions indicates that the initial yield of DNA double-strand breaks (DSBs) is independent of the SMF intensity. The DSB induction is predominantly attributed to the secondary electrons below a few tens of eV, of which energy deposition patterns are not considerably affected by the Lorentz force. Our simulation study suggests that treatment planning for MRgRT can be made with consideration of only changed dose distribution.

Incoherent Thomson scattering: future implementation and measurement capabilities on the PANDORA experiment

The PANDORA (Plasmas for Astrophysics Nuclear Decays Observation and Radiation for Archaeometry) experiment aims to study the β-decay process inside a dense plasma mimicking stellar conditions. An electron cyclotron resonance plasma trap will be built at INFN-LNS in Catania, Italy, for the generation of the desired conditions in the laboratory. This type of non-equilibrium dense plasma (reaching densities of up to 1013 cm−3) is expected to generate electron energy distribution functions with electron energies ranging from tens of eV up to tens of keV. In this work, we describe aspects of a planned implementation of an incoherent Thomson scattering diagnostic for the study of electron properties in the plasma trap of PANDORA. The performance of this high-sensitivity diagnostic, known as THETIS, has been previously validated in measurements across a range of low-density magnetized plasma environments and it is expected to provide access to electron energy information in PANDORA in the range of temperatures from 1 to 103 eV. This article will establish the potential of such a diagnostic for future characterization of the electron properties in the PANDORA experiment.

Optimized deceleration characteristics of multicharged ion beams from electron cyclotron resonance ion source

At present it is necessary the satellite lifetime 10-15 years for operating in space. Xenon is used as fuel for ion engines of satellites. There are problems of accumulated damages at irradiation and sputtering by low energy Xe ion from the engine. It is required to construct database of sputtering yield of ion beams in the low energy region from a hundred eV to 1keV. We are trying to investigate experimentally sputtering yield on satellite component by irradiating the low energy Xe q+ ion beams. We use the electron cyclotron resonance ion source (ECRIS) in the irradiation experiments. We decelerate the beam energy to several hundred eV after extraction at high voltage 10kV. It is found we cannot neglect the contribution of the space potential of the plasma in the ECRIS of several tens eV. We measured the plasma parameters and ion beam deceleration characteristics in operating conditions on ECRIS. As the results, it was found in operating ECRIS condition of low charge state ion being dominant that the space potential of the ECRIS has an effect of 10∼20% at the beam energy at about 100eV in conducting irradiation experiments on satellite component materials.

X-ray induced dynamics in borate glasses with different network connectivity

Hard x rays induce atomic dynamics in oxide glasses at doses low enough that the average structure is unchanged. X-ray photon correlation spectroscopy is used here to study this effect in a series of alkali borate glasses characterized by different network connectivity. The product of the x-ray dose rate per atom and the decay time of the density correlation function is a sample-dependent parameter with the dimensions of an energy: It varies between a fraction of eV and few tens of eV and is sensitive to the network connectivity of the glass. It can then be used to access some bonding information also in cases where the x rays perturb the material, a regime of great interest in modern x-ray-based experiments.

Energetic Neutral Atoms near Mars: Predicted Distributions Based on MAVEN Measurements

Abstract Through phase-space mapping 6 yr of H+, O+, and O 2 + distributions measured in situ by the Mars Atmosphere and Volatiles EvolutioN (MAVEN) orbiter, we derive semiempirical average energetic neutral atom (ENA) distributions near Mars. Differential fluxes of H-ENAs and O-ENAs are estimated by line-integrating ENA production and loss rates in the average phase-space ion distributions. By repeating the procedure for a systematic series of vantage points, we produce synthetic ENA observations for virtual circular orbits with radii twice that of Mars, revealing the angular dependence of the observer’s position. Accounting for known ENA production and loss terms, we find that H+ in the upstream solar wind yields total antisunward H-ENA fluxes of ∼3 × 105 cm−2 s−1. The dayside magnetosheath produces H-ENA angular-differential fluxes of up to 3 × 105 cm−2 s−1 sr−1, while the magnetosheath flanks populate the planet’s nightside with H-ENA fluxes in the range of 104–105 cm−2 s−1 sr−1. The O-ENA environment is dominated by a near-isotropic ∼105 cm−2 s−1 sr−1 relatively low-energy (tens of eV) population originating in the top-side ionosphere, particularly on the dayside. Lower fluxes (103–104 cm−2 s−1 sr−1) of energetic O-ENAs (≳100 eV) are mainly found on the nightside and above the electric polar regions of the induced magnetosphere. Asymmetries in the ENA flow are largely limited to the energetic O-ENA populations, while the H-ENA distribution is mostly symmetric around the Sun‒Mars line. We discuss how synthetic ENA observations can provide insight into the near-Mars space environment, including the planet’s plasma environment and exosphere.

Unravelling strong electronic interlayer and intralayer correlations in a transition metal dichalcogenide

Electronic correlations play important roles in driving exotic phenomena in condensed matter physics. They determine low-energy properties through high-energy bands well-beyond optics. Great effort has been made to understand low-energy excitations such as low-energy excitons in transition metal dichalcogenides (TMDCs), however their high-energy bands and interlayer correlation remain mysteries. Herewith, by measuring temperature- and polarization-dependent complex dielectric and loss functions of bulk molybdenum disulphide from near-infrared to soft X-ray, supported with theoretical calculations, we discover unconventional soft X-ray correlated-plasmons with low-loss, and electronic transitions that reduce dimensionality and increase correlations, accompanied with significantly modified low-energy excitons. At room temperature, interlayer electronic correlations, together with the intralayer correlations in the c-axis, are surprisingly strong, yielding a three-dimensional-like system. Upon cooling, wide-range spectral-weight transfer occurs across a few tens of eV and in-plane p–d hybridizations become enhanced, revealing strong Coulomb correlations and electronic anisotropy, yielding a two-dimensional-like system. Our result shows the importance of strong electronic, interlayer and intralayer correlations in determining electronic structure and opens up applications of utilizing TMDCs on plasmonic nanolithrography.

Monte-Carlo simulation and analytical expressions for the extrapolated range and transmission rate of low energy electrons [10 eV–10 keV] in 11 monoatomic materials

The “extrapolated range” of electrons is a very practical physical parameter widely used in many applications. The commonly used analytical expressions are given classically for energies down to ∼1 keV. Low energy Monte Carlo simulations have been performed to extract this parameter in various materials down to several tens of eV. These simulations have been used to parameter both, transmission probability and projected range analytical expressions. These empirical equations have been extended to 11 monoatomic elements (C, Be, Al, Si, Ti, Ni, Cu, Ge, Ag, Fe and W) and for energies ranging from ∼10 eV up to some tens of MeV.

Production of secondary electrons and photons and energy absorption mechanisms in amorphous carbon irradiated by photons in the energy range of 0.03 to 17.4 keV

Energy absorption mechanisms in amorphous carbon under irradiation by 0.03–17.4 keV photons is studied by Monte Carlo simulation with accounting for the cascade decays of inner-shell vacancies and tracking all secondary electrons and photons including very-low-energy ones. Energy absorption by the atoms of the sample that underwent initial ionization by incident photons is only important at energies of several tens of eV (UV and XUV range). The principal mechanism of energy absorption on the whole incident photon energy interval is through inelastic processes caused by secondary electrons. At incident photon energies above C1s ionization threshold low-energy KLL Auger electrons produced by the cascade decay of C1s vacancy transfer energy to the medium in the vicinity of the site of initial photoionization. At energies far above the C1s-threshold, high-energy photoelectrons spread the absorbed energy over larger volumes and with smaller density. A great portion of the energy brought by incident photons, about 42 %, is transferred to the medium by low-energy secondary electrons and photons that are incapable of ionizing or exciting the atoms of the sample. The number of low-energy electrons is proportional to the energy of an incident photon, and at incident photon energies of several keV, one initial photoionization produces hundreds of secondary low-energy electrons.

On the relationship between the plasma characteristics, the microstructure and the optical properties of reactively sputtered TiO2 thin films

A titanium target was reactively sputtered in an Ar/O2 atmosphere by (i) conventional direct current magnetron sputtering (DCMS), (ii) high-power impulse magnetron sputtering (HiPIMS), and (iii) bipolar HiPIMS (BPH) discharges for the deposition of titanium dioxide thin films without intentional heating and biasing. In the HiPIMS and BPH cases, the peak current density was set to either 0.32 A cm−2 or 0.86 A cm−2. The time-averaged power density delivered to the plasma was set to ≈1.2 W cm−2 in each case. For the BPH discharge, a positive pulse of +300 V was applied after the negative pulse to accelerate the positive ions toward the substrate. Energy-resolved mass spectrometry analysis has shown a low-energy peak for DCMS while a high energy tail extending in the range of several tens of eV was observed with HiPIMS. In the BPH discharge, the energy reached ≈300 eV for Ti+ ions, which is in agreement with the applied positive potential. According to the x-ray diffraction patterns, amorphous coatings were obtained with DCMS, while rutile TiO2 was obtained with both HiPIMS and BPH. However, in the BPH case, diffractograms were characterized by more intense high-angle diffraction peaks highlighting a modification of the growth process for these conditions. Rutherford backscattering spectrometry analysis has shown that a higher amount of argon atoms were incorporated into the TiO2 films which are found to be slightly understoichiometric for the BPH discharge. It was also found that the refractive index, n, varied as a function of the sputtering regime with the highest value obtained in the HiPIMS case (n = 2.73 at 550 nm). Finally, the experimentally determined optical data were compared to the ones extracted from NASCAM simulations which are found in good agreement except for the BPH case.

Counterstreaming ions at the inner pole of a magnetically shielded Hall thruster

During development testing of a 12.5 kW magnetically shielded Hall thruster, direct evidence of counterstreaming ions eroding the pole covers was found. One stream of ions appears to originate from the discharge channel while the other stream appears to originate from the centrally mounted cathode. Velocity distribution measurement indicates that each stream impacts the poles of the thruster at high oblique angles of incidence. While the average energy of each stream was in the tens of eV, the energy distributions contained high-energy tails that can be a major contributor to erosion. Starting with the physical picture of high oblique angle bombardment, predictions of change in erosion behavior over time are in good agreement with pole cover erosion measurements taken during wear testing. The new evidence points to a need to study these ions that are traditionally considered “low-energy” ions and the role they play in the erosion of the poles of magnetically shielded Hall thrusters.

Effect of native oxide on the crystal orientation contrast in SEM micrographs obtained at hundreds, tens and units of eV

This paper aims to elucidate the effect of native air-formed oxide on the crystallographic contrast between differently oriented copper grains in scanning electron microscope images obtained at energies from 0 eV up to 1 keV. The contrast between the Cu grains is strongly affected by the presence of native oxide. The crystallographic orientation contrast between the grains without covering the native oxide layer is relatively weak at hundreds of eV, negligible at tens of eV, and dramatically increases at energies below 10 eV. At extremely low landing energies, say below ~ 1 eV, the surface potential differences caused by work function variations between the differently oriented Cu grains affect the primary electrons, which enables us to obtain the micrographs with high crystallographic contrast. This contrast becomes surprisingly visible even if the grains are covered by a several nm thick native oxide layer. The presence of the native air-formed oxide layer on the Cu surface is inconsiderable for the contrast formation at energies close to the mirror conditions (< 1 eV). The surface potential differences originating in the substrate can affect the incident electrons through the native oxide film situated on the Cu surface. Scanning low-energy electron microscopy is a powerful tool for mapping local work function differences with a spatial resolution slightly better than 30 nm due to high sensitivity to local electrical potentials.

Fabrication of Bismuth Absorber Arrays for NTD-Ge Hard X-ray Microcalorimeters

The high-spectral-resolution detection of hard X-rays (E > 20 keV) is a challenging and nearly unexplored area in space astrophysics. Traditionally hard X-ray detectors present moderate spectral resolutions, although few tens of eV one could open new frontiers in the study of nuclear processes and high-temperature plasma dynamics in energetic processes. This can be achieved by using cryogenic microcalorimeters. Within a research activity aimed at developing arrays of neutron transmutation-doped germanium (NTD-Ge) microcalorimeters for the high-spectral-resolution detection (about 50 eV@60 keV) of hard X-rays (20 keV 60 μm) bismuth absorber arrays. The adopted technological process and the study of related process parameters are discussed; preliminary results on produced arrays are given.