Hot Ions Research Articles

Superthin current sheets supported by anisotropic electrons

Current sheets with strong transverse (cross field) currents are commonly observed in planetary magnetospheres and serve as a natural energy source for magnetic reconnection. As the most investigated current sheet, the current sheet in the Earth's magnetotail forms in a high-β plasma, with hot ions dominantly contributing to the diamagnetic currents. Spacecraft observations have shown, however, that a superthin electron dominated current sheet can be embedded in the Earth's magnetotail current sheet. In this paper, we develop a model of such superthin current sheets with strong currents produced by anisotropic electrons. We also compare the model with spacecraft observations, which shows reasonable agreement in spatial profiles and magnitudes of the current density. The spatial scale (thickness) of the superthin current sheet is controlled by the equatorial magnetic field component, whereas the current density magnitude is controlled by the electron fire-hose parameter at the equator. Although the current density peak within the superthin current sheet can significantly exceed the background (embedding) current density, the magnetic field magnitude at the superthin current sheet boundary does not exceed 10% of the total magnetic field magnitude. These superthin current sheets are sub-ion (or even electron-scale) structures, which are not sufficiently large/intense to perturb ion dynamics. We discuss applications of the proposed model for the analysis of plasma instabilities in superthin electron-dominated current sheets.

Direct measurement of recurrent fluorescence emission from naphthalene ions

In this study, the recurrent fluorescence of naphthalene ions was investigated using an electrostatic ion beam trap. The number of photons from the recurrent fluorescence on the ${D}_{2}\ensuremath{\rightarrow}{D}_{0}$ transition was measured as a function of time, after the production of naphthalene ions by electron impact. The emission of photons was observed over a time range of approximately 10 ms. The variation in the number of photons for such a long time range could be explained by conducting simulations using previously reported theoretical rate constants of both the fragmentation and the recurrent fluorescence of vibrationally hot naphthalene ions.

Solitary dispersive Alfven wave in a plasma with hot electrons, cold positrons and ions

The dispersion relation and the nonlinear behaviour of dispersive Alfven waves (DAWs) in a plasma, which is composed by hot electrons, cold positrons and ions, are studied from the multi-component fluid theory. It can be indicated from the linear dispersion relation that the coupling of positron acoustic waves with shear Alfven waves results from the effect of the finite ion gyroradius. In our mode, the pressure and the inertia of the positron acoustic wave are, respectively, provided by the hot electrons and the cold positrons, which are different from the ones in a plasma consisting of two-group positrons with different temperatures. Furthermore, the existence and properties of DAW solitons are analysed from the Sagdeev pseudopotential equation, which indicates the existence of super-Alfvenic or sub-Alfvenic solitary DAWs, as well as the amplitude and width of DAW solitons depend on the positron concentration and the electron temperature. When the effects of cold positrons can’t be neglected, there may coexist the compressive and rarefactive DAW solitons. When the concentration of positron is negligibly small, the properties of DAW solitons in our model are similar to the ones of kinetic Alfven wave solitons in a plasma composed by hot electrons and cold ions.

Ionization Efficiency in a Hot Flat Disc-Shaped Cavity

Hot cavity ion sources of different kinds are widely used in nuclear and mass spectroscopy, especially in on-line isotope separation devices attracting attention of scientists and engineers looking for high ionization efficiency, robustness and beam purity. In the paper a new type of hot ionizer cavity is proposed: namely cavity having the shape of a flat disc, which may be especially suitable for short-lived nuclides to be ionized.A numerical model of the ion source is presented in the paper. The particle tracking code takes into account ionization at hot surfaces and enables modeling of both flat disc cavity and standard elongated cavity ionizers. The code enables calculation of total ionization efficiency and is suitable for stable and long-lived nuclides.Influence of the flat disc cavity geometry (thickness and radius) and its temperature on total ionization efficiency was considered – it was shown that the efficiency increases with cavity radius due to the growing number of particle-wall collisions. This effect may be important in the case of the hard-to-ionize nuclides.The optimal ionizer geometry is characterized by 90 % efficiency, even for substances with rather low ionization coefficient (of order 0.05). The role played by the size of the extraction opening is explained – it is demonstrated that the ionization efficiency increases due to the opening radius reduction. It is also proven that extraction voltage of 1–2 kV is sufficient to maintain optimal ionizer efficiency.

PDA/Cu Bioactive Hydrogel with "Hot Ions Effect" for Inhibition of Drug-Resistant Bacteria and Enhancement of Infectious Skin Wound Healing.

Quick and effective sterilization of drug-resistant bacteria inevitably became an ever-growing global challenge. In this study, a multifunctional composite (PDA/Cu-CS) hydrogel mainly composed of polydopamine (PDA) and copper-doped calcium silicate ceramic (Cu-CS) was prepared. It was confirmed that PDA/copper (PDA/Cu) complexing in the composite hydrogel played a key role in enhancing the photothermal performance and antibacterial activity. Through a unique "hot ions effect", created by the heating of Cu ions through the photothermal effect of the composite hydrogel, the hydrogel showed high-efficiency, quick, and long-term inhibition of methicillin-resistant Staphylococcus aureus and Escherichia coli. In addition, the hydrogel possessed remarkable bioactivity to stimulate angiogenesis. The in vivo results confirmed that the "hot ions effect" of the composite hydrogel removed existing infection in the wound area efficiently and significantly promoted angiogenesis and collagen deposition during infectious skin wound healing. Our results suggested that the design of multifunctional hydrogels with "hot ions effect" may be an effective therapeutic approach for the treatment of infectious wounds.

Development of an Experimentally Validated MCNP6 Model for 11C Production via the 14N(p,α) Reaction Using a GE PETtrace Cyclotron

The General Electric (GE®) PETtrace 860 cyclotron at the Missouri University Research Reactor (MURR) facility is used extensively for medical and research radioisotope production. However, no model exists of its performance, and the proton beam’s energy and spatial distribution are unmeasured. Here, an MCNP6 model was developed to improve upon the performance of the cyclotron target systems that are routinely utilized for research and medical radioisotope production. Since the cyclotron beam energy and profile have a significant impact on the efficiency and character of radioisotope production, the MURR cyclotron proton beam energy was measured using high-purity copper stacked foil activation to be 14.6 ± 0.2 MeV, a significant reduction from the stated 16.4 MeV. Phosphor plate imaging was also used to radiographically image the distribution of radioisotope production within the copper foils and characterize the beam spatial and intensity profile. Total target activity was quantified by trapping the 11C on a solid adsorbent and measuring the amount in an ion chamber. Effective target densities were calculated for irradiations conducted with beam currents between 5 and 40 μA. The measured beam and target characteristics were used to develop an MCNP6 model of 11C production. Through use of the model, it was determined that the targets were, at most, 41% efficient as a thick target design resulting in up to 11.80-MeV average protons impinging on the target walls leading to potential contamination from hot ion recoils.

Dynamical properties and fractal patterns of nonlinear waves in solar wind plasma

We propose a dynamical model using traveling wave transformations from a three-component magnetized collisionless homogeneous plasma consisting of hot protons, hot heavier ions (He++), and kappa distributed electrons. The dynamical properties of the both perturbed and unperturbed dynamical systems are presented for both the slow and fast electrostatic structures. The external perturbation is a source of weak chaos, which can be quantified by the lyapunov exponents. It is also interesting to investigate how the fractal dimension changes with the initial conditions, whereas the parameters are fixed to some physical values. The results presented in the proposed study are relevant to the dynamical properties and fractal patterns of coherent electrostatic structures observed in the solar wind at 1 AU.

A small and round heliosphere suggested by magnetohydrodynamic modelling of pick-up ions

As the Sun moves through the surrounding partially ionized medium, neutral hydrogen atoms penetrate the heliosphere, and through charge exchange with the supersonic solar wind, create a population of hot pick-up ions (PUIs). Until recently, the consensus was that the shape of the heliosphere is comet-like. The termination shock crossing by Voyager 2 demonstrated that the heliosheath (the region of shocked solar wind) pressure is dominated by PUIs; however, the impact of the PUIs on the global structure of the heliosphere has not been explored. Here we use a novel magnetohydrodynamic model that treats the PUIs as a separate fluid from the thermal component of the solar wind. The depletion of PUIs, due to charge exchange with the neutral hydrogen atoms of the interstellar medium in the heliosheath, cools the heliosphere, ‘deflating’ it and leading to a narrower heliosheath and a smaller and rounder shape, confirming the shape suggested by Cassini observations. The new model reproduces both the properties of the PUIs, based on the New Horizons observations, and the solar wind ions, based on the Voyager 2 spacecraft observations as well as the solar-like magnetic field data outside the heliosphere at Voyager 1 and Voyager 2. A magnetohydrodynamic model of the interaction between the solar wind and the interstellar medium shows that our heliosphere has a round shape, not a tail-like shape as usually assumed. The model reproduces the observations from Cassini, New Horizons and the two Voyager probes.

Production of clean rare isotope beams at TRIUMF ion guide laser ion source

Hot cavity resonant ionization laser ion sources (RILIS) provide a multitude of radioactive ion beams with high ionization efficiency and element selective ionization. However, in hot cavity RILIS there still remains isobaric contaminations in the extracted beam from surface ionized species. An ion guide-laser ion source (IG-LIS) has been implemented that decouples the hot isotope production region from the laser ionization volume. A number of IG-LIS runs have been conducted to provide isobar free radioactive ion beams for experiments. Isobar suppression of up to 106 has been achieved, however, IG-LIS still suffers from an intensity loss of 50-100X as compared to hot cavity RILIS. Operating parameters for IG-LIS are being optimized and design improvements are being implemented into the prototype for robust and efficient on-line operation. Recent SIMION ion optics simulation results and the ongoing development status of the IG-LIS are presented.

A multi-fluid model of the magnetopause

Abstract. Observation of the solar wind–magnetosphere boundary provides a unique opportunity to investigate the physics underlying the interaction between two collisionless magnetized plasmas with different temperature, density and magnetic field topology. Their mixing across the interface as well as the boundary dynamics are affected by the development of fluid (and kinetic) instabilities driven by large-scale inhomogeneities in particle and electromagnetic fields. Building up a realistic initial equilibrium state of the magnetopause according to observations is still a challenge nowadays. In this paper, we address the modeling of the particles and electromagnetic field configuration across the Earth's magnetopause by means of a three-fluid analytic model. The model relies on one hot and one cold ion population as well as a neutralizing electron population. The goal is to create an analytic model that is able to reproduce the observations as closely as possible. Some parameters of the model are set using a fitting procedure that aims to minimize their difference with respect to experimental data provided by the Magnetospheric MultiScale (MMS) mission. All of the other profiles, concerning the electron pressure and the relative densities of the cold and hot ion populations, are calculated in order to satisfy the fluid equilibrium equations. Finally, using a new tri-fluid code, we check the stability of the large-scale equilibrium model for a given experimental case and provide proof that the system is unstable to reconnection. This model could be of interest for the interpretation of satellite results and for the study of the dynamics at the magnetosphere–solar wind boundary.

New insights on fast ion-acoustic soliton stopbands and extension to dusty plasmas

Large amplitude fast ion-acoustic solitons are revisited in a three-component plasma composed of cold ions, warm (adiabatic) ions, and hot Boltzmann electrons to determine where the limits occur in the ranges of the warm ion-to-electron temperature ratio τ and the charge-to-mass ratio of the cold ions relative to the warm ions μ for the existence of stopbands. The warm (adiabatic) ion limiting curve evolves in a similar fashion for increasing values of τ or decreasing values of μ in supporting the existence of stopbands when the warm ion limiting curve is double-valued in the Mach number over part of a range of cold ion densities, to the disappearance of the stopbands when the warm ion limiting curve is single-valued over the complete range of cold ion densities. The bifurcation of the warm ion limiting curve into an upper and lower branch indicates the transition region in parameter space, which is between the region where stopbands are supported and the region where stopbands do not occur. The stopbands are found to have an infinite extent over the range of cold ion densities in the transition region. The widening (or narrowing) of the stopbands over the range of cold ion densities associated with a kappa (or Cairns) distribution of hot ions in a four-component plasma is found to be much weaker than non-thermal electron effects on the stopbands as reported by Maharaj and Bharuthram [Phys. Plasmas 24, 022305 (2017)].

Cylindrical Magnetosonic Solitary Waves by Modified Korteweg–de Vries–Burgers Equation in Electron–Positron–Ion Plasma

Theoretical investigations are carried out for the cylindrical magnetosonic solitary waves in dissipative, hot electron–positron–ion plasma. By the reductive perturbation technique the modified Korteweg–de Vries–Burgers equation (mKdVB) is obtained and its approximate analytical solution is given. Using this solution, the effects of different physical parameters on magnetosonic solitary wave in cylindrical geometry are discussed. The results may have applications in laboratory and space plasmas.

Multipoint Observations of Magnetosheath Response to Foreshock Transients

AbstractMultispacecraft observations of the magnetosheath responses to various foreshock transients in a single event on 17 March 2004 are reported in this paper. The Cluster spacecraft recorded long‐standing large amplitude ULF waves with both compressive and transverse components in the magnetosheath. Additionally, two transient structures with depressions in density and magnetic field were observed in this period. One structure contains greatly heated and significantly deflected plasmas in the middle and a cold solar wind population at its trailing edge, which is identified as a spontaneous hot flow anomaly with a remnant of the foreshock caviton. It is transmitted through the magneosheath and evolved into a magnetosheath cavity. This cavity was subsequently encountered by the Double Star TC‐1 spacecraft deeper inside the magnetosheath. Meantime, fluxes of hot ions in the energy range of 5–38 keV exhibit quasiperiodic variations. These energetic ions are earthward with pitch angle distributions of alternately field aligned or antifield aligned. A correlation between its flux variations and the transverse fluctuations of the ULF waves is found. Moreover, magnetosheath filamentary structures with a series of anticorrelated oscillations of density and temperature were observed simultaneously.

Tracking Counterpart Signatures in Saturn's Auroras and ENA Imagery During Large‐Scale Plasma Injection Events

AbstractSaturn's morningside auroras consist mainly of rotating, transient emission patches, following periodic reconnection in the magnetotail. Simultaneous responses in global energetic neutral atom (ENA) emissions have been observed at similar local times, suggesting a link between the auroras and large‐scale injections of hot ions in the outer magnetosphere. In this study, we use Cassini's remote sensing instruments to observe multiple plasma injection signatures within coincident auroral and ENA imagery, captured during 9 April 2014. Kilometric radio emissions also indicate clear injection activity. We track the motion of rotating signatures in the auroras and ENAs to test their local time relationship. Two successive auroral signatures—separated by ~4 hr UT—form postmidnight before rotating to the dayside while moving equatorward. The first has a clear ENA counterpart, maintaining a similar local time mapping throughout ~9 hr observation. Mapping of the ionospheric equatorward motion post‐dawn indicates a factor ~5 reduction of the magnetospheric source region's radial speed at a distance of ~14‐20 RS, possibly a plasma or magnetic boundary. The second auroral signature has no clear ENA counterpart; viewing geometry was relatively unchanged, so the ENAs were likely too weak to detect by this time. A third, older injection signature, seen in both auroral and ENA imagery on the nightside, may have been sustained by field‐aligned currents linked with the southern planetary period oscillation system, or the re‐energization of ENAs around midnight local times. The ENA injection signatures form near magnetic longitudes associated with magnetotail thinning.

Modulation of Whistler Mode Waves by Ion‐Scale Waves Observed in the Distant Magnetotail

AbstractWave activities in tailward flows have been explored in the distant magnetotail at ~54 RE, where the coupling between whistler mode waves and ion‐scale waves was observed. The whistler mode waves periodically appeared at each cycle of the ion‐scale waves, and the electron distribution functions associated with the whistler mode waves showed enhancement in the direction parallel to background magnetic field. Wave analyses show that the field‐aligned electron components act as the energy source of the whistler mode waves. The ion‐scale waves are generated by the interaction of the hot ion beam with background ions. A likely candidate of the ion‐scale wave is the kinetic Alfven wave, which can generate the enhanced field‐aligned electron populations by the parallel electric field.

Hot WHIM counterparts of FUV O VI absorbers: Evidence in the line-of-sight towards quasar 3C 273

Aims. We explore the high spectral resolution X-ray data towards the quasar 3C 273 to search for signals of hot (∼106−7 K) X-ray-absorbing gas co-located with two established intergalactic far-ultraviolet (FUV) O VI absorbers. Methods. We analyze the soft X-ray band grating data of all XMM-Newton and Chandra instruments to search for the hot phase absorption lines at the FUV predicted redshifts. The viability of potential line detections is examined by adopting the constraints of a physically justified absorption model. The WHIM hypothesis is investigated with a complementary 3D galaxy distribution analysis and by detailed comparison of the measurement results to the WHIM properties in the EAGLE cosmological, hydrodynamical simulation. Results. At one of the examined FUV redshifts, z = 0.09017 ± 0.00003, we measured signals of two hot ion species, O VIII and Ne IX, with a 3.9σ combined significance level. While the absorption signal is only marginally detected in individual co-added spectra, considering the line features in all instruments collectively and assuming collisional equilibrium for absorbing gas, we were able to constrain the temperature (kT = 0.26 ± 0.03 keV) and the column density (NH × Z⊙/Z = 1.3−0.5+0.6 × 1019 cm−2) of the absorber. Thermal analysis indicates that FUV and X-ray absorption relate to different phases, with estimated temperatures, TFUV ≈ 3 × 105, and, TX − ray ≈ 3 × 106 K. These temperatures match the EAGLE predictions for WHIM at the FUV/X-ray measured Nion-ranges. We detected a large scale galactic filament crossing the sight-line at the redshift of the absorption, linking the absorption to this structure. Conclusions. This study provides observational insights into co-existing warm and hot gas within a WHIM filament and estimates the ratio of the hot and warm phases. Because the hot phase is thermally distinct from the O VI gas, the estimated baryon content of the absorber is increased, conveying the promise of X-ray follow-up studies of FUV detected WHIM in refining the picture of the missing baryons.

Convection in the Magnetosphere of Saturn During the Cassini Mission Derived From MIMI INCA and CHEMS Measurements

AbstractAn extensive analysis of Cassini Ion and Neutral Camera (INCA) and Charge Energy Mass Spectrometer (CHEMS) measurements of ~6–231 keV ion anisotropies acquired during selected spin and stare periods for nearly all mission orbits has been completed. Based on this analysis, we find that the computed azimuthal speed of Saturn's magnetodisk plasma increases within the inner and middle magnetosphere. Beyond the orbit of Titan, in the magnetotail, the calculated rotation speed remains roughly constant with increasing distance from Saturn. The component of convection parallel to Saturn's spin axis is smaller and on average nearly zero. The radial speed of plasma shows distinct local time dependence and increases outward with increasing distance down the magnetotail. The magnetodisk flow remains primarily azimuthal to large distances, indicating the plasma is still under the influence of Saturn as it transits across the nightside. Tailward flows have been observed in the region near the dawn and dusk magnetotail flanks. The plasma flow in the predawn quadrant is much more disorganized than that in the premidnight quadrant. The hydrogen and oxygen hot ion temperatures increase with decreasing distance to Saturn. Some plasma evidently escapes into a dusk boundary layer at the dusk magnetotail flank, while the remaining plasma primarily moves across the magnetotail and is entrained into the flow of a boundary layer at the dawn flank of the magnetotail. When scaled to the magnetopause standoff distance and corotation fraction, the convection speed of plasma in the magnetospheres of Jupiter and Saturn is similarly organized.

Ultrafast hot ion-exchange triggered electrocatalyst modification and interface engineering on silicon photoanodes

Slow charge transfer kinetics and poor stability are two critical issues for silicon (Si) photoanodes in photoelectrochemical (PEC) water splitting. Herein, a facile and ultrafast interfacial reaction was performed on n-Si/Ni for stable and high-performance Si photoanode by regulating both the Ni electrocatalyst and Si surface. The calculated and experimental results reveal that highly catalytic oxygen vacancies-rich Fe:NiOOH layer will be formed on Ni surface during the hot Fe ions exchange reaction, which can create abundant active sites for oxygen evolution reaction (OER). The interfacial reaction also can modulate the interfacial state of Si photoanode to increase barrier height for n-Si/Ni/Fe:NiOOH photoanode, thereby accelerating the charge separation and transportation. More significantly, a thin iron silicide (FeSi2) layer will be generated on Si surface (Ni-free region), which is beneficial for the stability of Si photoanode. This work provides a low-cost and straightforward approach to design high-performance Si photoanodes by interface engineering and electrocatalyst defects regulation.

Comparative study of dust acoustic solitons in two-temperature ion homogeneous and inhomogeneous plasmas

The dust acoustic solitary waves are theoretically investigated in dusty plasmas for different cases of with and without density gradients. These low-frequency solitary waves are studied using appropriate Korteweg–de Vries equations obtained using relevant stretched coordinates. The soliton solutions in homogeneous plasma, weakly inhomogeneous plasma and strongly inhomogeneous plasma, are thoroughly investigated for studying the effect of different parameters like dust charge and density of all the plasma species on the soliton profiles. The combination of the dust charge with its number density changes the dynamics of the solitons and that is further affected by the number density of the hot ion with respect to the cold ions.

Radioactive ion beam manipulation at the IGISOL-4 facility

The IGISOL-4 facility in the JYFL Accelerator Laboratory of the University of Jyvaskyla (JYFL-ACCLAB) produces low-energy radioactive ion beams, primarily for nuclear spectroscopy, utilizing an ion guide-based, ISOL-type mass separator. Recently, new ion manipulation techniques have been introduced at the IGISOL-4 including the application of the PI-ICR (Phase-Imaging Ion Cyclotron Resonance) technique at the JYFLTRAP Penning trap, as well as commissioning of a Multi-Reflection Time-Of-Flight (MR-TOF) separator/spectrometer. The successful operation of the MR-TOF also required significant improvement of the Radio-Frequency Quadrupole (RFQ) cooler and buncher device beam pulse time structure. In addition, laser ionization techniques have been developed for particular cases, for example, a hot cavity laser ion source for silver production. A new stable isotope ion source and a beam line has been introduced for tuning and calibration purposes. In addition to the installations at the IGISOL-4 facility, the extension of the vacuum-mode recoil separator MARA (Mass Analysing Recoil Apparatus), MARA-LEB (MARA Low Energy Branch) has been under development. MARA-LEB will utilize the gas-cell technique and laser ionization to convert MeV-scale radioactive beams to low-energy ones.