Ion Velocity Research Articles

Initial kinetics of electrons, ions and electric field in planar vacuum diode with plasma cathode

The paper presents the results of a 1D1V theoretical study of the initial stage of plasma expansion into a planar vacuum gap 1 cm long with an applied voltage of 500–5000 V. Based on the collisionless kinetic and Maxwell equations, the motion of a two-component electron–ion plasma in a self-consistent electric field is described. The fundamental mechanism of ‘superthermal’ velocities of the emission edge of the plasma and anode-directed velocities of positive ions is demonstrated in detail. The general regularities of this process are established for variations in the number density of the initial plasma and the applied voltage.

Bohm sheath criterion and dust charging for active magnetized plasma in the presence of q-nonextensive electron distribution

We have investigated the Bohm sheath criterion and evolution of dust charge at the sheath edge for the collisional active magnetized plasma in the presence of q-nonextensive electron distribution. The set of governing equations has been numerically solved for given initial conditions, whereas the dust charging equation has been solved using the –Raphson method. The Bohm sheath condition for active plasma has been extended using the Sagdeev potential approach, and it has been found that gas pressure, obliqueness of the magnetic field, source and sink terms, and choice of electron distribution affect the Bohm velocity, sheath thickness, floating potential, and evolution of dust charge. As the magnetic field, gas pressure, and nonextensive parameter q increase, the Bohm velocity is found to be decreasing (from supersonic to subsonic), and its explicit effect can be seen on the dust charging process. The magnitude of the E × B drift velocity of ions at the sheath edge determines the Bohm velocity, floating potential, and dust screening length as well. Furthermore, we have presented the comparison of the obtained results for two different cases: (i) unmagnetized and magnetized cases and (ii) active and quiescent plasmas.

2D kinetic simulations of whistler wave generation by nonlinear scattering of lower-hybrid waves in turbulent plasmas

Turbulent plasmas in space, laboratory experiments, and astrophysical domains can often be described by weak turbulence theory, which can be characterized as a broad spectrum of incoherent interacting waves. We investigate a fundamental nonlinear kinetic mechanism of weak turbulence that can explain the generation of whistler waves in homogeneous plasmas by nonlinear scattering of short wavelength electrostatic lower-hybrid (LH) waves. Two particle-in-cell (PIC) simulations with different mass ratios in two dimensions (2D) were performed using a ring ion velocity distribution to excite broadband LH waves. The wave modes evolve in frequency, and wavenumber space such that the LH waves are converted to whistler waves. The simulations show the formation of quasi-modes, which are low-frequency density perturbations driven by the ponderomotive force due to the beating of LH and whistler waves. These low-frequency oscillations are damped due to resonant phase matching with thermal plasma particles. By comparing the phase and thermal speeds, we confirm the nonlinear scattering mechanism and its role in the 2D evolution of the ring ion instability. Although the nonlinear scattering is theoretically slower in 2D than in 3D due to the absence of the vector nonlinearity, these simulations show that quasi-modes are an important diagnostic for nonlinear landau damping in PIC simulations that has not been utilized in the past. The nonlinear scattering mechanism described here plays an important role in the generation of whistler waves in active experiments, which will be experimentally studied in the upcoming Space Measurement of a Rocket Release Turbulence experiment.

Plasma Ion Velocity Distribution Function Perturbed by Ion-Acoustic Solitons: Analytical Calculations Based on KDV Equation

Plasma Ion Velocity Distribution Function Perturbed by Ion-Acoustic Solitons: Analytical Calculations Based on KDV Equation

Plasma Ion Velocity Distribution Function Perturbed by Ion-Acoustic Solitons: Analytical Calculations Based on KDV Equation

Using the Korteweg–De Vries equation, for background plasma, the distribution functions perturbed by ion-acoustic solitons are calculated. For describing the perturbed distribution functions, the explicit formula is obtained, which is suitable for practical applications. The results are compared with the analytical calculations and simulation results obtained previously.

Dynamic Processes Associated With Prominent Ionospheric Variations in a Narrow Longitudinal Zone Near the EIA Crest Region as Revealed by ICON Satellite and Ground Beidou Receiver Observations Over South Asia

AbstractNeutral winds and plasma motions from the Ionospheric Connection Explorer mission were used to investigate dynamic processes associated with large regional total electron content (TEC) differences in a narrow longitudinal zone exceeding ∼45 TECU obtained from dense Beidou geostationary receivers at low latitudes over South Asia. The TEC east‒west asymmetry was defined to quantify this difference, which exceeded ∼5 TECU per 1° longitude distance and occurred around the equatorial ionization anomaly (EIA) crest on 31 March 2021 under geomagnetically quiescent conditions. Moreover, the magnetic meridional ion velocity exhibited a large longitude difference around the EIA crest during periods with strong ionospheric east‒west asymmetry. Furthermore, the longitude difference variation was consistent with the TEC east‒west asymmetry variation during 11–21 March 2020 and 27 March–4 April 2021. No significant correlations between TEC east‒west asymmetry and longitude differences under conditions with neutral winds and magnetic zonal ion drifts were observed in either case. The different vertical plasma drifts could contribute to ionospheric changes with a zonal range of a few hundred kilometers.

Azimuthal ion movement in HiPIMS plasmas—part I: velocity distribution function

Magnetron sputtering discharges feature complex magnetic field configurations to confine the electrons close to the cathode surface. This magnetic field configuration gives rise to a strong electron drift in azimuthal direction, with typical drift velocities on the order of 100 km s−1. In high power impulse magnetron sputtering plasmas, the ions have also been observed to follow the movement of electrons with velocities of a few km s−1, despite being not magnetized. In this work, we report on measurements of the azimuthal ion velocity using spatially resolved optical emission spectroscopy, allowing for a more direct measurement compared to experiments performed using mass spectrometry. The azimuthal ion velocities increase with target distance, peaking at about 1.55 km s−1 for argon ions and 1.25 km s−1 for titanium ions. Titanium neutrals are also found to follow the azimuthal ion movement which is explained with resonant charge exchange collisions. The experiments are then compared to a simple test-particle simulation of the titanium ion movement, yielding good agreement to the experiments when only considering the momentum transfer from electrons to ions via Coulomb collisions as the only source of acceleration in azimuthal direction. Based on these results, we propose this momentum transfer as the primary source for ion acceleration in azimuthal direction.

Deep insight on efficiency of deposited energy within sensitive volumes for characterizing basic mechanism of single event upset saturated cross-section regarding implicit inaccuracy

The Single Event Upset (SEU) characterization on the partially depleted (PD) Silicon-On-Insulator (SOI) SRAMs manufactured by 0.5/0.35 μm CMOS technology has been studied by using the experimental accelerator’s testing and Monte Carlo simulation. The results show that, in spite of the good consistent between the simulated data and experimental testing, one notable phenomenon is that, linear energy transfer (LET) as the input has no manifest influence on the saturation of SEU cross-section. This non-negligible trend led us to use the term ion velocity instead of LET. The characteristics of ion velocity have certainly been proved by the experiment, while the unsimilar results are found for the simulation with no any difference from the SEU cross-section. Consequently, a more straightforward calculation in the deposited energy within sensitive volume (SV) has performed by inspecting directly into the underlying mechanism of the undetected energy loss. The loss of deposited energy has been obtained in the assumption that the heavy ions strike on the hypothetical device at oblique incidence. The unexpected energy loss resulted from incident ions at oblique incidence as edge effect indicates the importance of quantifying the efficiency of energy collection with respect to the dimensions of SV, including the variance of surface area and thickness. It is illustrated that the deposited energy induced by heavy ions on the condition of changeable surface area has more sensitivity on the incident angle and ionic characterization compared with those for the SV of variable thicknesses. Moreover, it is obtained that the fractional changes of deposited energy within the SVs of different thicknesses present a saturating trend, which can be accelerated by the increment of incident angle, and this evidence would be helpful for deeply comprehending why the implicit inaccuracy of the SEU saturated cross-section happened under the metrics of LET or ion velocity. Ultimately, the dependence of deposited energy on the surface area and thickness is further explored and discussed based on the geometrical property and radial track profile.

Effect of Many-Particle Interactions on the Transport Properties of Low-Energy Ions in Carbon Nanotubes

Using the method of molecular dynamics, the significance of many-particle interactions in the dynamics of low-energy ions in carbon nanotubes is studied, and the necessity of taking into account such interactions in the corresponding molecular dynamics calculations is shown. The effect of elastic perturbations of the carbon nanotube wall on the motion of ions inside the nanotube channel has been studied. It was found that the ion energy losses decrease by a factor of 1.5–3 when the influence of the perturbation of the carbon nanotube wall on the motion of ions is taken into account when the ion velocity approaches the perturbation propagation velocity. It has also been shown that the effect of the interaction between moving ions and perturbations of the carbon nanotube wall becomes more monotonic with a decrease in the magnitude of thermal fluctuations of the nanotube wall, in terms of energy losses by ions. Within the framework of the model under consideration, the stopping power of the electron gas bound to the atoms that form the walls of a carbon nanotube is small compared to the energy losses of ions due to elastic collisions with nanotube atoms.

Ionosphere-thermosphere coupling via global-scale waves: new insights from two-years of concurrent in situ and remotely-sensed satellite observations

Growing evidence indicates that a selected group of global-scale waves from the lower atmosphere constitute a significant source of ionosphere-thermosphere (IT, 100–600 km) variability. Due to the geometry of the magnetic field lines, this IT coupling occurs mainly at low latitudes (< 30°) and is driven by waves originating in the tropical troposphere such as the diurnal eastward propagating tide with zonal wave number s = −3 (DE3) and the quasi-3-day ultra-fast Kelvin wave with s = −1 (UFKW1). In this work, over 2 years of simultaneous in situ ion densities from Ion Velocity Meters (IVMs) onboard the Ionospheric Connection Explorer (ICON) near 590 km and the Scintillation Observations and Response of the Ionosphere to Electrodynamics (SORTIE) CubeSat near 420 km, along with remotely-sensed lower (ca. 105 km) and middle (ca. 220 km) thermospheric horizontal winds from ICON’s Michelson Interferometer for Global High-resolution Thermospheric Imaging (MIGHTI) are employed to demonstrate a rich spectrum of waves coupling these IT regions. Strong DE3 and UFKW1 topside ionospheric variations are traced to lower thermospheric zonal winds, while large diurnal s = 2 (DW2) and zonally symmetric (D0) variations are traced to middle thermospheric winds generated in situ. Analyses of diurnal tides from the Climatological Tidal Model of the Thermosphere (CTMT) reveal general agreement near 105 km, with larger discrepancies near 220 km due to in situ tidal generation not captured by CTMT. This study highlights the utility of simultaneous satellite measurements for studies of IT coupling via global-scale waves.

Are the oscillations found in magnetized collisional electronegative warm plasma artifact during plasma-surface interaction?

The formation of the sheath and its characteristics are investigated in an electronegative plasma under the impact of an oblique and constant magnetic field. Specifically, the role of the magnetic field and initial conditions of positive ion velocity on the sheath characteristics are uncovered by adopting the Sagdeev potential approach for the determination of the modified Bohm’s criterion. At the sheath edge, the upper and lower components of the positive ion velocity perpendicular to the probe/wall are determined and examined in greater detail. The sheath structure is found to be modified considerably by the initial conditions. If the magnetic field is strong near the sheath edge, then the profile of the positive ion density shows a pulse-like structure for the case when we neglect the x-component (parallel to the wall) of positive ion velocity at the sheath edge. This pulse-like structure disappears when all the components of the positive ion velocity at the sheath edge are included, i.e. the ions are considered to move in any direction but towards the probe. The occurrence or disappearance of pulse-like structures or oscillations completely depend upon the initial conditions. Since in real situations the ions are expected to move in any direction (carrying all their velocity components) and are not aligned only in the direction perpendicular to the wall, these oscillations are artifact in nature. The sheath thickness is observed to be reduced with increasing magnetic field strength and its inclination. In order to better understand the phenomenon, isothermal and adiabatic cases are also discussed.

Evidence of non-Maxwellian ion velocity distributions in spherical shock-driven implosions.

The ion velocity distribution functions of thermonuclear plasmas generated by spherical laser direct drive implosions are studied using deuterium-tritium (DT) and deuterium-deuterium (DD) fusion neutron energy spectrum measurements. A hydrodynamic Maxwellian plasma model accurately describes measurements made from lower temperature (<10keV), hydrodynamiclike plasmas, but is insufficient to describe measurements made from higher temperature more kineticlike plasmas. The high temperature measurements are more consistent with Vlasov-Fokker-Planck (VFP) simulation results which predict the presence of a bimodal plasma ion velocity distribution near peak neutron production. These measurements provide direct experimental evidence of non-Maxwellian ion velocity distributions in spherical shock driven implosions and provide useful data for benchmarking kinetic VFP simulations.

Abnormal Sub‐Auroral Ion Drifts (ASAID) Developed in the Postmidnight (1–4) Magnetic Local Time Sector in 2013

AbstractWe investigate the Abnormal Sub‐Auroral Ion Drifts (ASAID) developed in the postmidnight (1–4) magnetic local time sector in 2013. Shown by the Defense Meteorological Satellite Program F15 horizontal ion velocity measurements, we specified 21 antisunward (eastward) ASAID flow channels (FCs) based on their respective underlying polar convections. Overall, the polar convection formed a two‐cell pattern with its convection axis tilted in the morning‐evening direction because of the underlying BY &lt; 0 conditions. Its dawn cell intruded into the duskside from the dawnside where the eastward ASAID flows were streaming antisunward, opposite to the dawn cell sunward convection flows. Mostly, the ASAID FC appeared in the coinciding ring‐current–related ionospheric trough and flow‐stagnation–related main ionospheric trough in the South American sector because of the favorable conditions created by the South Atlantic Magnetic Anomaly promoting also the development of Stable Auroral Red (SAR) arc. Rarely observed, the ASAID FC was associated with the SAR arc detected over Rothera. Detected in the Mid Pacific longitude sector, a pair of northern‐southern ASAID FCs demonstrated northern‐southern conjugacy. With correlated observations, demonstrating magnetosphere‐ionosphere conjugacy, the inward (earthward) ASAID electric (E) field could also be investigated. These reveal the ASAID E field's fast‐time development by short‐circuiting when the hot‐ring‐current—cold‐plasmasphere interface developed and became impacted by finite Larmor radius effects because of the earthward intrusion of hot ring current protons. The ASAID E field's inner‐magnetosphere environment was characterized by the hot zone where heating was generated by low‐frequency waves and auroral kilometric radiations.

Indirect Observations of Electric Fields at Comet 67P

AbstractNo spacecraft visiting a comet has been equipped with instruments to directly measure the static electric field. However, the electric field can occasionally be estimated indirectly by observing its effects on the ion velocity distribution. We present such observations made by the Rosetta spacecraft on 19 April 2016, 35 km from the nucleus. At this time comet 67P was at a low outgassing rate and the plasma environment was relatively stable. The ion velocity distributions show the cometary ions on the first half of their gyration. We estimate the bulk drift velocity and the gyration speed from the distributions. By using the local measured magnetic field and assuming an E × B drift of the gyrocentre, we get an estimate for the average electric field driving this ion motion. We analyze a period of 13 hr, during which the plasma environment does not change drastically. We find that the average strength of the perpendicular electric field component is 0.21 mV/m. The direction of the electric field is mostly anti‐sunward. This is in agreement with previous results based on different methods.

The impact of quantized magnetic pressure on the stimulated Brillouin scattering of electromagnetic waves

Within the frame work of Landau quantization theory of Fermi gas, we formulate here the exotic physics of magnetic stimulated Brillouin scattering instability (MSBS) arising due to the nonlinear interaction of high frequency electromagnetic waves (EMWs) with degenerate, strongly magnetized electron-ion plasma. Quantum magneto hydrodynamic model (QMHD) is followed to develop the basic differential equations of quantized magnetosonic waves (QMWs) in the presence of super strong magnetic (SSH) field, whereas Maxwell equations are used to derive the governing differential equation of pump EMWs. The nonlinear interaction of EMWs and QMWs is addressed by employing the phasor matching technique. The obtained dispersion relation of MSBS shows that for a fixed density of fermions, the SSH field alone suppresses the MSBS instability as a function of quantized magneto ion velocity (C He ) and the Alfven speed (V A ) via three-wave decay and modulational instabilities. However, for particular condition the MSBS instability is found to increase as a function of SSH field. Next, the analytical results are verified numerically and graphically for soft x-rays in the environment of neutron star. The present MSBS analysis may be critical in neutron stars, radio pulsars and magnetars having super strong magnetic field i.e. even larger than the quantum threshold value i.e, H ∼ 4.4 × 1013 G, or in any application where the enhancement or suppression of SBS may be important.

Particle simulation on the ion acceleration in vacuum arc discharge

The supersonic ion jet generated in vacuum arc plasma has numerous applications, but the ion acceleration mechanism is incompletely understood. In this paper, a one-dimensional spherical vacuum arc discharge model is established, and the ion acceleration from vacuum breakdown to steady arc stage is investigated using particle-in-cell direct simulation Monte Carlo method. The results show that a potential hump exists and locates about far away from the cathode, but the potential drop provides a small contribution to the ion acceleration. A potential valley forms near the plasma–vacuum boundary and propagates towards the anode as the plasma expands during the vacuum breakdown stage. The ion mounting this valley experiences continuous acceleration by the dynamic electric field of the potential valley. As the plasma reaches the anode, a steady arc stage is gradually build-up, and the potential valley disappears. Consequently, the maximum mean ion velocity decreases. The source dominating the ion acceleration in this stage is turned into the electron–ion Coulomb collision.

Numerical Investigation on the Height and Intensity Variations of Sporadic E Layers at Mid‐Latitude

AbstractIn previous studies, various physical parameters, such as vertical wind shear null, vertical ion velocity null (IVN), and maximum gradient of vertical ion velocity, have been used as an indicator of Es layer height in light of the wind shear theory. Using a numerical Es layer model, we investigated which parameter represents the height of Es layer over Wuhan (114.4°E, 30.5°N) most precisely. The simulation results show that the height of Es layer above 110 km depends most strongly on the height of vertical IVN. However, below 110 km, the height of vertical IVN does not always agree with the height of Es layer. The analysis of simulation results suggests that the vertical gradient of the ratio of the ion‐neutral collision frequency (νi) to the ion gyrofrequency (ωi) affects the Es layer formation at lower altitudes (below 110 km). We also examined the effect of electric fields on the height and intensity of Es layers over Wuhan. It is found that eastward/upward electric fields can lift the Es layer height and reduce the Es layer intensity.

Introduction of Al(III)‐Ion‐Based Solid Polymer Electrolyte Material for Energy Storage Device Applications

AbstractSolid phase electrolyte system PVIm‐R‐PEG‐AlCl3 is introduced for Al(III) ion‐based energy storage material. Here, we introduced [AlCl3Br]− counter anion system with N‐octyl‐polyvinyl imidazolium polymer matrix supported by PEG. Electrolyte material shows good thermal stability with a Glass transition temperature (Tg~148 °C), which provides a good working temperature range for material processing. PVIm‐R‐PEG‐AlCl3 shows electrochemical stability of 1.5 V and red‐ox properties, it has 96 % of ionic conduction against the Al metal. The conductivity of electrolyte material is found in the range of 10−5 S/cm at room temperatures and 10−4 S/cm at higher temperature (&gt;40 °C). The polymer electrolyte matrix shows the mobility of 1.37×10−6 m2/Vs and drift ionic velocity of 3.42×10−4 m/s at 30 °C. The ionic movement of Al(III) ions inside the matrix follows correlated type hopping with the activation energy of 0.266 eV. This Al(III) ion‐based solid polymer electrolyte (SPE) is associated with a large amount of capacitance with a tiny electrode contribution.

Antisunward Streaming Westward Sub‐Auroral Ion Drifts (SAID) Developed in the Postmidnight (1–4) Magnetic Local Time Sector During 2013

AbstractIn this study, we have surveyed the Defense Meteorological Satellite Program F15 plots of horizontal ion velocity measurements for the calendar year of 2013 and specified 15 antisunward (westward) sub‐auroral ion drifts (SAID) detections taken in the 1–4 magnetic local time (MLT) sector based on their respective underlying polar convections. We find that during these 15 SAID events, the strong duskside westward polar plasma convection extended across the midnight meridian into the postmidnight 1–4 MLT sector making there the westward SAID flows streaming antisunward. These antisunward (westward) SAID flows were observed only once as a northern‐southern conjugate pair over the Mid Pacific and repeatedly in the South American longitude sector's wider region. We could correlate six antisunward (westward) SAID flows with their respective nearby outward SAID E fields observed by one of the Van Allen Probe (VAP) satellites in the inner magnetosphere. These provided two strong correlations depicting inner‐magnetosphere—topside‐ionosphere conjugate observations and four weak correlations. The VAP observations illustrate (a) the newly‐formed outward SAID E field and (b) its plasma environment still showing (c) the signatures of short‐circuiting across (d) the newly‐formed plasmapause appearing with (e) the hot zone on the earthward/tailward side and sometimes with (f) a localized heat source. Implying different underlying heating mechanisms, the hot zone and the heat source were associated with energetic plasma particles accelerated by plasma turbulence, low‐frequency waves including electromagnetic ion cyclotron waves, and/or auroral kilometric radiation bursts.

Observations and Modeling of Unstable Proton and α Particle Velocity Distributions in Sub-Alfvénic Solar Wind at Parker Solar Probe Perihelia

Past observations show that solar wind (SW) acceleration occurs inside the sub-Alfvénic region, reaching the local Alfvén speed at typical distances ∼10–20 solar radii (R s ). Recently, Parker Solar Probe (PSP) traversed regions of sub-Alfvénic SW near perihelia in encounters E8–E12 for the first time, providing data in these regions. It became evident that the properties of the magnetically dominated SW are considerably different from the super-Alfvénic wind. For example, there are changes in the relative abundances and drift of α particles with respect to protons, as well as in the magnitude of magnetic fluctuations. We use data of the magnetic field from the FIELDS instrument, and construct ion velocity distribution functions (VDFs) from the sub-Alfvénic regions using Solar Probe ANalyzer for Ions data, and run 2.5D and 3D hybrid models of proton-α sub-Alfvénic SW plasma. We investigate the nonlinear evolution of the ion kinetic instabilities in several case studies, and quantify the transfer of energy between the protons, α particles, and the kinetic waves. The models provide the 3D ion VDFs at the various stages of the instability evolution in the SW frame. By combining observational analysis with the modeling results, we gain insights on the evolution of the ion instabilities, the heating and the acceleration processes of the sub-Alfvénic SW plasma, and quantify the exchange of energy between the magnetic and kinetic components. The modeling results suggest that the ion kinetic instabilities are produced locally in the SW, resulting in anisotropic heating of the ions, as observed by PSP.