Ion Velocity Research Articles

Dominant impact of Ion velocity on defect formation in suspended graphene

Dominant impact of Ion velocity on defect formation in suspended graphene

Comparative Analysis of Plasma Sheath Characteristics in One‐Dimensional and Three‐Dimensional Velocity Spaces Governing Nonextensive Electron Density

ABSTRACTIn this study, we developed a model to explore the characteristics of a magnetized plasma sheath, containing positive ions, electrons, and neutral particles. The ions are described using a fluid model based on the continuity and momentum equations, while the electron distribution is analyzed using three cases: the Maxwell–Boltzmann distribution and the Tsallis distribution in both 1‐D and 3‐D velocity spaces. Applying the Sagdeev method, we established the modified Bohm sheath criterion to obtain the required ion velocity at the sheath entrance for all three cases. The lower Mach number limit for Bohm velocity modification depends on factors such as ion temperature, ionization frequency, collision frequency, magnetic field angle, nonextensive parameter , and the velocity space governing the density of nonextensive electrons, independent of magnetic field magnitude. Additionally, the electron velocity distribution was analyzed for various q‐values, revealing that in 3‐D velocity space, the energy range is broad and extensive, while in 1‐D velocity spaces, it is narrower and confined within the broader 3‐D interval. We examined the influence of key parameters on sheath characteristics under the Maxwellian distribution, as well as in 1‐D and 3‐D velocity spaces for the Tsallis distribution. The results demonstrated significant differences between the three cases, showing that in the 3‐D case, the sheath thickness expands more compared to the 1‐D and the Maxwell–Boltzmann distribution. This underscores the significance of accounting for the dimensionality of velocity space when investigating plasma sheath phenomena. Such understanding is crucial for optimizing plasma‐surface interactions in various applications.

Extreme Heating of Minor Ions in Imbalanced Solar-wind Turbulence

Abstract Minor ions in the solar corona are heated to extreme temperatures, far in excess of those of the electrons and protons that comprise the bulk of the plasma. These highly nonthermal distributions make minor ions sensitive probes of the collisionless processes that heat the corona and power the solar wind. The recent discovery of the “helicity barrier” offers a mechanism in which imbalanced Alfvénic turbulence in low-β plasmas preferentially heats protons over electrons, generating high-frequency, proton-cyclotron-resonant fluctuations. We use the hybrid-kinetic particle-in-cell code Pegasus++ to drive imbalanced Alfvénic turbulence in a 3D low-β plasma with additional passive ion species, He2+ and O5+. A helicity barrier naturally develops, followed by clear phase-space signatures of oblique proton-cyclotron-wave heating and Landau-resonant heating from the imbalanced Alfvénic fluctuations. The former results in characteristically arced ion velocity distribution functions, whose non-bi-Maxwellian features are shown by linear ALPS calculations to be critical to the heating process. Additional features include a steep transition-range electromagnetic spectrum, proton-cyclotron waves propagating in the direction of the imbalance, significantly enhanced proton-to-electron heating ratios, ion temperatures that are considerably more perpendicular with respect to magnetic field, and extreme heating of heavier species in a manner consistent with mass scalings inferred from spacecraft measurements. None of these features are realized in an otherwise equivalent simulation of balanced turbulence. If seen simultaneously in the fast solar wind, these signatures of the helicity barrier would testify to the necessity of incorporating turbulence imbalance in a complete theory for the evolution of the solar wind.

Gas-Phase Scattering of Transition Metal Atoms Fe, Ir, and Pt with CH4, O2, and CO2.

Understanding the interactions between transition metal atoms and molecules is important for the study of various related chemical and physical processes. In this study, we have investigated collisions between iron (Fe), iridium (Ir), and platinum (Pt) and the small molecules CH4, O2, and CO2 using a crossed-beam and time-sliced ion velocity map imaging technique. Elastic collisions were observed in all cases, except for collisions of Pt with O2 and CO2. Collisions of Fe or Ir with CH4, O2, and CO2 show mainly long-range attractive potentials at large impact parameters leading to forward scattering, whereas sideways and backward scatterings indicate the formation of short-lived complexes with lifetimes comparable to their rotational periods. In collisions of Pt with O2 and CO2, Pt may react with the gases and become chemically bound to them, which can deplete the nonreactive scattering signal. The insights gained from this study provide a foundation for improved understanding of the complex interactions between transitional metal atoms and other molecules.

Unveiling ultraviolet photodissociation dynamics of SiO from a laser-ablated supersonic beam with time-sliced ion velocity imaging.

SiO is a widespread molecule found in interstellar space, and its dissociation requires a substantial input of energy due to its high bond energy of 8.34 eV. The present study initially demonstrated across a broad range of ultraviolet (UV) wavelengths (243-288 nm) the one-photon and two-photon dissociation of SiO molecules, which were generated from the laser ablation of a Si rod colliding with an oxygen molecular beam. The images of Si products obtained through time-sliced ion velocity mapping have revealed the existence of distinct dissociation channels, encompassing Si(3P) + O(3P), Si(1D) + O(3P), Si(1D) + O(1D) and Si(1S) + O(1D) from the photodissociation of vibrationally excited SiO(X1Σ+, v) and low-lying electronically excited SiO(C1Σ-, D1Δ, a3Σ+, b3Π, d3Δ and e3Σ-) states. These findings contribute to a more comprehensive understanding of silicon chemistry during the combustion of silica-rich meteorites in the Earth's atmosphere, and have wider implications in the fields of atmospheric chemistry, astrochemistry, and combustion science.

Collisional radiative model based investigation on the color appearance of xenon plasma in Hall thruster plumes

Abstract Hall thruster is a type of electric propulsion system used for spacecraft. The study of the Hall thruster plume, which is a plasma, reveals the thruster’s performance. Images of Hall thruster operating can be found from various online sources, the thruster plumes are typically transparent with a slight blue or green hue. However, some plumes are colorful instead of being monochromatic, with distinguishable regions. In this study, we investigated the xenon plasma color using a collisional radiative model and explained the color appearance of Hall thruster plumes. We show that xenon atoms and ions appear in different colors. For a standard observer, singly charged xenon ions appear in green, irrespective of the plasma environment. Xenon atoms, on the other hand, can appear blue, violet, or magenta. Through the investigation, we found that the resulting plasma color is related to the mass utilization efficiency and ion velocity of the thruster plume. We introduce an approach to produce color from collisional radiative models, where we use color as a property of the plasma, and demonstrate its usefulness for plasma studies.

Two-dimensional cooling without repump laser beams through ion motional heating

Laser cooling typically requires one or more repump lasers to clear dark states, which complicates experimental setups, especially for systems with multiple repumping frequencies. Here, we demonstrate cooling of Be+ ions using a single laser beam, enabled by micromotion-induced one-dimensional heating. By manipulating the displacement of Be+ ions from the trap’s nodal line, we precisely control the ion micromotion velocity, eliminating the necessity of a 1.25 GHz offset repump laser while keeping ions cold in the direction perpendicular to the micromotion. We use two equivalent schemes, cooling laser detuning and ion trajectory imaging to measure the speed of the Be+ ions, with results accurately reproduced by molecular dynamics simulations based on a machine learned time-dependent electric field inside the trap. This work provides a robust method to control micromotion velocity of ions and demonstrates the potential of micromotion-assisted laser cooling to simplify setups for systems requiring multiple repumping frequencies.

The Ion Formation and Quantitative Response of Isoprene, Monoterpenes and Terpenoids in Ion Mobility Spectrometry with Atmospheric-Pressure Chemical Ionization as a Function of Temperature.

Ion mobility spectrometry is successfully used as a sensor technology for different applications. A feature of this method is that characteristic ion mobility spectra are obtained for each measurement rather than a sum signal. The spectra result from the different drift velocities of ions in a drift tube at atmospheric pressure. In this study, we investigated the ion formation processes and the quantitative response of isoprene, monoterpenes and monoterpenoids as a function of the temperature of the spectrometer using a tritium ionization source. These substances are important target analytes in atmospheric monitoring and in the analysis of essential oils in different matrices. A drift tube temperature above 120 °C permitted the most sensitive detection of isoprene and monoterpenes, while 80 °C was sufficient for the sensitive detection of most terpenoids. Dimer ions were formed for isoprene over the whole temperature range. The ionization processes of monoterpenes and terpenoids were strongly influenced by the temperature. At temperatures of 40 °C, adduct ions were formed in addition to MH+ ions for monoterpenes. Enhanced temperatures provided a single peak with the same drift time for all monoterpenes. Structural differences influenced the ion formation of terpenoids, and much more complex spectra were obtained. The nature of the product ions changed depending on the temperature.

Effect of Ion‐Neutral Collisions on the Plasma Sheath in the Presence of Surface‐Produced Negative Ions

ABSTRACTThe effect of ion‐neutral collisions on the plasma sheath has been investigated for electronegative plasma in the presence of surface‐produced negative ions. Such sheath structures are commonly found in the negative ion sources. It has been found that ion‐neutral collisions reduce the ion velocity towards the sheath and consequently reduce the negative ion production from the surface. The space charge profile shows peak near the sheath edge in contrast to the common case where it has a peak near the wall. The fractional loss of the ions at the wall along with the ion impact energy is calculated.

Investigation of two-dimensional radio-frequency sheath properties using a microscale fluid model

Abstract In previous work (Kohno H. and Myra J.R. 2023 Comput. Phys. Commun. 291 108841), we developed a numerical scheme based on a two-dimensional microscale radio-frequency (RF) sheath model with periodically curved wall boundaries. Here, we expand the capability of this scheme through modification of the boundary conditions (BCs) on the conducting walls, which allows the ion flow to turn back to the plasma at locations on the walls where the electromagnetic force on the ions is reversed from its usual direction. Numerical simulations are carried out to investigate the dependences of the surface-integrated admittances on the wall bump height, ion magnetization, ion mobility, and the magnetic field angle, and to visualize the sheath structures in several cases. One of the main results is the ion cyclotron admittance resonance observed under the condition of low ion mobility (high normalized frequency). It is shown that the amplitude of the resonance peak depends on the wall bump height and the ion velocity is reversed on the sides of the bump in an RF cycle for the resonance cases. Furthermore, the differences in the admittances between the one- and two-dimensional microscale models are assessed for the purpose of understanding non-locality of the sheath near the wall surface for the parameters considered in this study. This information will be essential for improving the sheath BC for macroscale calculations in the future.

Simultaneous Infrared Observations of the Jovian Auroral Ionosphere and Thermosphere.

Simultaneous observations of and in Jupiter's northern infrared aurora were conducted on 02 June 2017 using Keck-NIRSPEC to produce polar projection maps of radiance, rotational temperature, column density, and radiance. The temperature variations within the auroral region are K, generally consistent with previous studies, albeit with some structural differences. Known auroral heating sources including particle precipitation, Joule heating, and ion drag have been examined by studying the correlations between each derived quantity, yet no single dominant mechanism can be identified as the main driver for the energetics in Jupiter's northern auroral region. It appears that a complex interaction exists between the heating driven by various mechanisms and the cooling from the thermostat effect. Comparisons between the temperature and the line-of-sight ion velocity in the reference frame of (a) the planetary rotation and (b) the neutral atmosphere further suggest that the local thermodynamic equilibrium effect may play an important role in thermospheric heating at Jupiter. Along with previously reported heating events that occurred in both the lower and upper atmosphere, it is speculated that the heating source may originate from an altitude above Jupiter's stratosphere but below the peak altitude of overtone and quadrupole emissions.

Numerical Simulation and Experimental Research on High-power Plasma Generator

Abstract High power energy output is achieved through a plasma generator, which has great application scenarios in the fields of phase change work and spray damage. However, the plasma concentration between electrodes is high, the temperature is high, and the motion speed is high. The physical environment is complex, and the time scale is extremely small. It is difficult to directly measure parameters such as ion temperature and ion velocity distribution through experiments. This article is based on the magneto-hydro-dynamics (MHD) model and sets boundary conditions based on experimental research results to model and simulate the magnetic flow field of a generator containing plasma. The model takes into account the physical properties of multiple components of plasma, and analyzes the flow field characteristics of the plasma generator under high-energy action based on the simulation results.

Towards independent thrust and specific impulse control in a three-stage µCAT-MPD thruster

Space has been becoming increasingly more commercialized and, as a result, more accessible. Higher demand and technological advancement has driven this expansion and lead to the standardization of low-formfactor satellites, CubeSats. These small systems can provide various services, ranging from GPS and network-building to Earth remote-sensing and weather-monitoring. Unfortunately, the operational time of these satellites is significantly limited by their ability to perform station-keeping maneuvers for long periods of time. Small electric propulsion systems, with their low complexity and high impulse, are a promising solution to this problem. In this work we experimentally investigate performance characteristics (ion velocity and thrust) of the laboratory model of novel three-stage configuration of micro-cathode arc thruster (µCAT) small propulsion system for CubeSats. We found that depending on the voltage on the second stage, ion velocity can grow (from 8 to around 20 km/s) with the third-stage voltage, while the maximal thrust values (more than 1 mN) are achieved at the maximal (120 V) positive voltages on both stages. These findings represent the next step towards controllable multimodality of the low-power vacuum arc thrusters for micro-satellites.

Cross-Scale Energy Transfer from Fluid-Scale Alfvén Waves to Kinetic-Scale Ion Acoustic Waves in the Earth's Magnetopause Boundary Layer.

In space plasmas, large-amplitude Alfvén waves can drive compressive perturbations, accelerate ion beams, and lead to plasma heating and the excitation of ion acoustic waves at kinetic scales. This energy channeling from fluid to kinetic scales represents a complementary path to the classical turbulent cascade. Here, we present observational and computational evidence to validate this hypothesis by simultaneously resolving the fluid-scale Alfvén waves, kinetic-scale ion acoustic waves, and their imprints on ion velocity distributions in the Earth's magnetopause boundary layer. We show that two coexisting compressive modes, driven by the magnetic pressure gradients of Alfvén waves, not only accelerate the ion tail population to the Alfvén velocity, but also heat the ion core population near the ion acoustic velocity and generate Debye-scale ion acoustic waves. Thus, Alfvén-acoustic energy channeling emerges as a viable mechanism for plasma heating near plasma boundaries where large-amplitude Alfvén waves are present.

On the importance of slow ions in the kinetic Bohm criterion

Between a plasma and a solid target lies a positively charged sheath of several Debye lengths $\lambda _{D}$ width, typically much smaller than the characteristic length scale $L$ of the main plasma. This scale separation implies that the asymptotic limit $\epsilon = \lambda _{D} / L \rightarrow 0$ is useful to solve for the plasma-sheath system. In this limit, the Bohm criterion must be satisfied at the sheath entrance. A new derivation of the kinetic criterion, admitting a general ion velocity distribution, is presented. It is proven that, for $\epsilon \rightarrow 0$ , the distribution of the velocity component normal to the target, $v_x$ , and its first derivative must vanish for $|v_x| \rightarrow 0$ at the sheath entrance. These two conditions can be subsumed into a third integral one after it is integrated by parts twice. A subsequent interchange of the limits $\epsilon \rightarrow 0$ and $|v_x| \rightarrow 0$ is invalid, leading to a divergence which underlies the misconception that the criterion gives undue importance to slow ions.

Calculation and Evaluation of Neutral Winds in the Lower Thermosphere Based on SYISR Observations

AbstractAn algorithm for obtaining ion vector velocities and neutral winds in the lower thermosphere (100–150 km) was applied to the Sanya incoherent scatter radar (SYISR; located at 18.3°N, 109.6°E) for the first time. The observational experiment transmitted alternating code pulses with a code width of 20 μs. The ion vector velocities and neutral winds were derived from multiple‐beam line‐of‐sight ion velocities. To verify the reliability, we first analyzed the variations and errors of the ion vector velocity and the neutral wind at different time scales. Then, we used an empirical model (HWM) and a theoretical model (NCAR‐TIEGCM) for comparison. Both comparisons exhibited good consistency in terms of neutral wind velocity. Furthermore, we compared the SYISR neutral winds with the meteor radar and ICON/MIGHTI winds. The zonal (meridional) wind speeds of the meteor radar and SYISR are 24.95 m/s (13.95 m/s) and 20.68 m/s (16.85 m/s), respectively, at 6:30 LT at 100 km. The amplitudes and phases of the tides derived from the SYISR data are in accordance with those of the meteor radar. The ICON/MIGHTI and SYISR showed consistencies in terms of the wind velocity when ignoring interannual variation.

Measurements of F1‐ Region Ionosphere State Variables at Arecibo Through Quasi Height‐Independent Exhaustive Fittings of the Incoherent Scatter Ion‐Line Spectra

AbstractWe discuss an exhaustive search approach to fit the incoherent scatter spectrum (ISS) in the F1‐region for molecular ion fraction (fm), ion temperature (Ti), and electron temperature (Te). The commonly used “full profile” approach for F1‐region measurements parameterizes the molecular ion fraction as a function of altitude and fits all the related heights for the state variables. In our approach, we fit the ISS at each height for fm, Ti, Te, and ion velocity (Vi) independently. Our exhaustive search method finds all the major local minima at each altitude. Although a parameterized function is used to guide the algorithm in finding the best solution, the fitting parameters retain their local characteristics. Despite that fitting fm, Ti, and Te without constraints requires Doppler shift to be accurately determined and the ISS signal‐to‐noise ratio higher than the full‐profile method, simulations show that Ti, Te, and fm can be recovered within a few percent accuracy with a moderate signal‐to‐noise ratio. We apply the exhaustive search approach to the Arecibo high‐resolution incoherent scatter radar data taken on 13 September 2014. The derived ion and electron temperatures are sensitive enough to reveal thermosphere gravity waves commonly seen in the electron density previously. Our method is more robust than previous height‐independent fitting methods. Comparison with another Arecibo program indicates our results are likely more accurate. Simultaneous high‐resolution measurements of Ti, Te, fm, Vi, and electron concentration (Ne) in our approach open new opportunities for synergistic studies of the F1‐region dynamics and chemistry.

Driven two-fluid slow magnetoacoustic waves in the solar chromosphere with a realistic ionisation profile

Context. This study was carried out in the context of chromosphere heating. Aims. This paper aims to discuss the evolution of driven slow magnetoacoustic waves (SMAWs) in the solar chromosphere modelled with a realistic ionisation profile and to consider their potential role in plasma heating and the generation of plasma outflows. Methods. Two-dimensional (2D) numerical simulations of the solar atmosphere are performed using the JOANNA code. The dynamic behaviour of the atmospheric plasma is governed by the two-fluid equations (with ionisation and recombination terms taken into account) for neutrals (hydrogen atoms) and ions (protons)+electrons. The initial atmosphere is described by a hydrostatic equilibrium (HE) supplemented by the Saha equation (SE) and embedded in a fanning magnetic field. This initial equilibrium is perturbed by a monochromatic driver which operates in the chromosphere on the vertical components of the ion and neutral velocities. Results. Our work shows that the HE+SE model results in time-averaged (net) plasma outflows in the top chromosphere, which are larger than their pure HE counterpart. The parametric studies demonstrate that the largest chromosphere temperature rise occurs for smaller wave driving periods. The plasma outflows exhibit the opposite trend, growing with the driver period. Conclusions. We find that the inclusion of the HE+SE plasma background plays a key role in the evolution of SMAWs in the solar atmosphere.

Wave steepening and shock formation in ultracold neutral plasmas

We present observations of wave steepening and signatures of shock formation during expansion of ultracold neutral plasmas formed with an initial density distribution that is centrally peaked and decays exponentially with distance. The plasma acceleration and velocity decrease at large distance from the plasma center, leading to central ions overtaking ions in the outer regions and the development of a steepening front that is narrow compared to the size of the plasma. The density and velocity change dramatically across the front, and significant heating of the ions is observed in the region of steepest gradients. For a reasonable estimate of electron temperature, the relative velocity of ions on either side of the front modestly exceeds the local sound speed (Mach number M≳1). This indicates that by sculpting steep density gradients, it is possible to create the conditions for shock formation, or very close to it, opening a new avenue of research for ultracold neutral plasmas.

Theoretical study of particle and energy balance equations in locally bounded plasmas

In this study, new particle and energy balance equations have been developed to predict the electron temperature and density in locally bounded plasmas. Classical particle and energy balance equations assume that all plasma within a reactor is completely confined only by the reactor walls. However, in industrial plasma reactors for semiconductor manufacturing, the plasma is partially confined by internal reactor structures. We predict the effect of the open boundary area ( ) and ion escape velocity ( ) on electron temperature and density by developing new particle and energy balance equations. Theoretically, we found a low ion escape velocity ( / ) and high open boundary area ( ) to result in an approximately 38% increase in electron density and an 8% decrease in electron temperature compared to values in a fully bounded reactor. Additionally, we suggest that the velocity of ions passing through the open boundary should exceed under the condition .