Plasma Torus Research Articles

Variability of the Auroral Footprint of Io Detected by Juno-JIRAM and Modelling of the Io Plasma Torus

Variability of the Auroral Footprint of Io Detected by Juno-JIRAM and Modelling of the Io Plasma Torus

Ion-molecule charge exchange in Io's extended atmosphere: Velocity dependence

The Io plasma torus is mostly composed of electrons and ions of O and S, singly and multiply-charged. These ions interact with the neutral species of Io's atmosphere (S, O, SO2 and SO) through symmetrical (e.g., O+ + O ⇒ O + O+) and asymmetrical (e.g., S+ + O ⇒ S + O+) charge exchange reactions. Moreover, molecular ions (SO2+, SO+) produced in Io's atmosphere by ionization or charge exchange are accelerated as they are picked up by the local plasma flow and eventually also charge exchange with the atmospheric neutrals (e.g., SO2+ + SO2 ⇒ SO2 + SO2+).Cross sections for many charge exchange reactions were estimated in Johnson and Strobel (1982) and McGrath and Johnson (1989) for ion speeds of 60 km/s appropriate for torus/neutral cloud interactions where the plasma is approximately at corotation in Io's reference frame. But close to Io, the flow velocity and ion temperature are drastically reduced (Vflow < 10 km/s and Tion < 50 eV) and greatly increased on its flanks (∼80 km/s and 400 eV). Thus, velocity-dependent charge exchange cross sections are critical for numerical simulations of the Io plasma/atmosphere interaction.We provide estimates of charge exchange cross sections of ions on molecular neutrals and of molecular ions on neutrals for the range of velocity [5–120] km/s representative of ion velocities at Io. We combine several methods valid at the low and higher velocities in this range: Two-state impact parameter approximation, quasi-thermal rate constant extrapolation, Langevin orbiting cross sections and scaling from experimental data. We describe these methods in details.Our estimates at 60 km/s are 2–3 times smaller or larger than previously published values, depending on the reaction. Most are generally large (∼60–90 Å2) at small velocities. We discuss the most important reactions relevant to Io's interaction and where improvements and experimental values are needed. We anticipate the effect of these velocity-dependent cross sections in numerical simulations of Io's interaction and show that some of these reactions are of critical importance regarding the plasma composition close to Io, the plasma supply to the torus and the neutral supply to Io's corona and to the giant neutral clouds that extend along Io's orbit.

Lost alpha Faraday cup foil noise characterization during Joint European Torus plasma post-processing analysis.

Capacitive plasma pickup is a well-known and difficult problem for plasma-facing edge diagnostics. This problem must be addressed to ensure an accurate and robust interpretation of the real signal measurements vs noise. The Faraday cup fast ion loss detector array of the Joint European Torus (JET) is particularly prone to this issue and can be used as a testbed to prototype solutions. The issue of separation and distinction between warranted fast ion signal and electromagnetic plasma noise has traditionally been solved with hardware modifications, but a more versatile post-processing approach is of great interest. This work presents post-processing techniques to characterize the signal noise. While hardware changes and advancements may be limited, the combination with post-processing procedures allows for more rapid and robust analysis of measurements. The characterization of plasma pickup noise is examined for alpha losses in a discharge from JET's tritium campaign. In addition to highlighting the post-processing methodology, the spatial sensitivity of the detector array is also examined, which presents significant advantages for the physical interpretation of fast ion losses.

Broadband Energization of Superthermal Electrons in Jupiter’s Inner Magnetosphere

AbstractThe Juno spacecraft in a polar orbit around Jupiter has observed broadband electron energization signatures at high latitudes (Mauk et al., 2017, https://doi.org/10.1038/nature23648). We investigate the origin of this energization by simulating the propagation of dispersive Alfvén waves from the Io plasma torus to high latitudes. These waves may be triggered by mechanisms such as the moon‐magnetosphere interaction or inflows from radial transport. We build on the initial hybrid gyrofluid‐kinetic electron simulation of Damiano et al. (2019, https://doi.org/10.1029/2018gl081219) to further quantify electron energization by Alfvénic waves, and investigate this process as a local source mechanism for observed broadband superthermal electron populations. We find that the magnitude of energization increases with the wave amplitude, while decreasing the radial wavelength reduces the high‐latitude wave and particle energy flux. Over the examined range of initial conditions we successfully generate broadband electron populations consistent with Juno observations (Mauk et al., 2017, http://doi.org/10.1038/nature23648; Szalay et al., 2018, https://doi.org/10.1029/2018je005752), that contribute to both precipitating populations and those that form trans‐hemispheric beams. Our energized electron distributions are consistent with observed superthermal populations critical for the torus energy budget (Bagenal &amp; Delamere, 2011, https://doi.org/10.1029/2010ja016294) and Io‐related auroral emission.

Field Line Resonances and Cavity Modes at Earth and Jupiter

Ultra-Low-Frequency (ULF) waves provide a means for the rapid propagation of energy and field-aligned current in planetary magnetospheres. At Earth, the ULF frequency range is usually defined as including waves with periods of 0.2–600 s; however, at Jupiter these waves can extend to periods of tens of minutes. In both magnetospheres, shear mode Alfvén waves can form field line resonances that exist between the ionospheres, with periods of a few minutes at Earth and a few tens of minutes at Jupiter. A major distinction between these two magnetospheres is in the density distribution. Earth has a dense ionosphere full of heavy ions, an extended, cold plasmasphere and a relatively low-density plasma sheet. In contrast, at Jupiter, the ionosphere is largely hydrogen (both in atomic form and in the H3+molecular ion), there is no appreciable plasmasphere and the plasma disk is dense and populated with heavy ions (largely sulfur and oxygen) originating at the moon Io and to some extent from other moons. As at Earth, the sharp Alfvén speed gradient above the ionosphere forms an ionospheric Alfvén resonator at Jupiter with periods of seconds. Furthermore, the high-latitude lobes at Jupiter have very low density and a resonant structure can be formed by waves bouncing between the ionosphere and the dense plasma disk. This structure leads to periods of tens of seconds. Finally, the dense Io plasma torus and plasma sheet provide conditions for compressional cavity modes to form in this region. Thus, the structure of the field line resonance modes is quite different at the two planets. Implications of these resonances on auroral particle acceleration will be discussed.

Simulation Model of Low-pressure Mercury-argon Torus Plasma Generated in Inductive Fluorescent Lamp

Simulation Model of Low-pressure Mercury-argon Torus Plasma Generated in Inductive Fluorescent Lamp

Determining the fuel ion ratio for D(T) and T(D) plasmas at JET using neutron time-of-flight spectrometry

The fusion fuel ion ratio, , is an important plasma parameter that needs to be tuned to maximize the power of a tokamak type fusion reactor. It is recognized as a parameter required for optimizing several ITER operating scenarios, and will likely be continuously monitored in future high-performance fusion devices such as DEMO. Tritium was recently introduced in the Joint European Torus (JET) plasma for the first time since the 1997 DTE1 and 2003 TTE campaigns, enabling the possibility to investigate fuel ion ratios. We present a method for measuring using neutron time-of-flight (TOF) spectrometry. By fitting the measured neutron spectral features, the relative reaction rate intensities between different ion species can be inferred, from which the fuel ion ratio can be extracted for a corresponding modeled reactivity. Unlike previous measurements of using neutron spectrometry, we utilize the neutron energy continuum produced in the three-body TT reaction to determine the fuel ion ratio for plasmas with large concentrations of tritium. Furthermore, the use of neutron TOF spectrometry has never previously been demonstrated for evaluating . The method is applied to TOF spectra acquired with TOFOR (JET name KM11) and shown to be consistent with the optical JET diagnostic KT5P which uses optical spectroscopy of a modified Penning gauge plasma to measure tritium and deuterium concentrations in the divertor exhaust gas.

Scattering and resonant frequency of a toroidal plasma covered by a dielectric layer

In this study, by calculating the electric potential related to the toroid cold plasma covered with a dielectric layer, we obtain resonant frequency of this configuration in two different states of polarization of the incident electric field. We consider the incident electric field along the parallel to the axis of the torus and along the perpendicular to the axis of the torus. By solving the Laplace equation and using the appropriate boundary conditions in the toroidal coordinates, we calculate the electrical potential inside plasma and dielectric layer and outside the considered configuration. Then resonant frequency of the toroid plasma derived. Furthermore, the electrical field inside the plasma is calculated. Then, we plot the normalized resonant frequency and the normalized amplitudes of the potentials for different polarizations of the electric field numerically. The resonant frequency as function of geometry and dielectric constant are calculated. It is assumed that the wavelength of incident wave is much greater than the dimensions of the cross section of the plasma torus.

Reflection and Refraction of the L-O Mode 5kHz Saturn Narrowband Emission by the Magnetosheath.

The reflection‐by‐sheath mechanism of 5 kHz narrowband emissions (NB) at Saturn is confirmed by Cassini observations during several crossings of the magnetopause, which show that the 5 kHz NB can be prevented from escaping Saturn's magnetosphere. The L‐O mode 5 kHz NB remained visible in areas of low plasma density but disappeared in regions of high plasma density. In three cases, NB disappeared immediately after the crossings of Saturn's magnetopause. A possible reflected NB event observed near the magnetosheath is discussed. This mechanism can help explain the 5 kHz NB observed at low latitudes outside the Enceladus plasma torus and their upper frequency limit variations. This mechanism significantly improves the current understanding of the 5 kHz NB.

Self-Sustained Divertor Oscillation Driven by Magnetic Island Dynamics in Torus Plasma

A new type of self-sustained divertor oscillation is discovered in the Large Helical Device stellarator, where the peripheral plasma is detached from material diverters by means of externally applied perturbation fields. The divertor oscillation is found to be a self-regulation of an isolated magnetic field structure (the magnetic island) width induced by a drastic change in a poloidal inhomogeneity of the plasma radiation across the detachment-attachment transitions. A predator-prey model between the magnetic island width and a self-generated local plasma current (the bootstrap current) is introduced to describe the divertor oscillation, which successfully reproduces the experimental observations.

Investigation of the compact torus plasma motion in the KTX-CTI device based on circuit analyses

Compact torus (CT) injection is one of the most promising methods for the central fuelling of next-generation reactor-grade fusion devices due to its high density, high velocity, and self-contained magnetised structure. A newly compact torus injector (CTI) device in Keda Torus eXperiment (KTX), named KTX-CTI, was successfully developed and tested at the University of Science and Technology in China. In this study, first, we briefly introduce the basic principles and structure of KTX-CTI, and then, present an accurate circuit model that relies on nonlinear regression analysis (NRA) for studying the current waveform of the formation region. The current waveform, displacement, and velocity of CT plasma in the acceleration region are calculated using this NRA-based one-dimensional point model. The model results were in good agreement with the experiments. The next-step upgrading reference scheme of the KTX-CTI device is preliminarily investigated using this NRA-based point model. This research can provide insights for the development of experiments and future upgrades of the device.

In situ observations of ions and magnetic field around Phobos: the mass spectrum analyzer (MSA) for the Martian Moons eXploration (MMX) mission

The mass spectrum analyzer (MSA) will perform in situ observations of ions and magnetic fields around Phobos as part of the Martian Moons eXploration (MMX) mission to investigate the origin of the Martian moons and physical processes in the Martian environment. MSA consists of an ion energy mass spectrometer and two magnetometers which will measure velocity distribution functions and mass/charge distributions of low-energy ions and magnetic field vectors, respectively. For the MMX scientific objectives, MSA will observe solar wind ions, those scattered at the Phobos surface, water-related ions generated in the predicted Martian gas torus, secondary ions sputtered from Phobos, and escaping ions from the Martian atmosphere, while monitoring the surrounding magnetic field. MSA will be developed from previous instruments for space plasma missions such as Kaguya, Arase, and BepiColombo/Mio to contribute to the MMX scientific objectives.

Looking into the cradle of the grave: J22564–5910, a potential young post-merger hot subdwarf

Context. We present the discovery of J22564–5910, a new type of hot subdwarf (sdB) which shows evidence of gas present in the system and it has shallow, multi-peaked hydrogen and helium lines which vary in shape over time. All observational evidence points towards J22564–5910 being observed very shortly after the merger phase that formed it. Aims. Using high-resolution, high signal-to-noise spectroscopy, combined with multi-band photometry, Gaia astrometry, and TESS light curves, we aim to interpret these unusual spectral features. Methods. The photometry, spectra, and light curves were all analysed, and their results were combined in order to support our interpretation of the observations: the likely presence of a magnetic field combined with gas features around the sdB. Based on the triple-peaked H lines, the magnetic field strength was estimated and, by using the SHELLSPEC code, qualitative models of gas configurations were fitted to the observations. Results. All observations can either be explained by a magnetic field of ∼650 kG, which enables the formation of a centrifugal magnetosphere, or a non-magnetic hot subdwarf surrounded by a circumstellar gas disc or torus. Both scenarios are not mutually exclusive and both can be explained by a recent merger. Conclusions. J22564–5910 is the first object of its kind. It is a rapidly spinning sdB with gas still present in the system. It is the first post-merger star observed this early after the merger event, and as such it is very valuable system to test merger theories. If the magnetic field can be confirmed, it is not only the first magnetic sdB, but it hosts the strongest magnetic field ever found in a pre-white dwarf object. Thus, it could represent the long sought-after immediate ancestor of strongly magnetic white dwarfs.

Plasma Stability in a Tokamak with Reactor Technologies Taking into Account the Pressure Pedestal

Studying stationary regimes with high plasma confinement in a tokamak with reactor technologies (TRT) [1] involves calculating the plasma stability taking into account the influence of the current density profiles and pressure gradient in the pedestal near the boundary. At the same time, the operating limits should be determined by the parameters of the pedestal, which, in particular, are set by the stability limit of the peeling–ballooning modes that trigger the peripheral disruption of edge localized modes (ELM). Using simulation of the quasi-equilibrium evolution of the plasma by the ASTRA and DINA codes, as well as a simulator of magnetohydrodynamic (MHD) modes localized at the boundary of the plasma torus based on the KINX code, stability calculations are performed for different plasma scenarios in the TRT with varying plasma density and temperature profiles, as well as the corresponding bootstrap current density in the pedestal region. At the same time, experimental scalings for the width of the pedestal are used. The obtained pressure values are below the limits for an ITER-like plasma due to the lower triangularity and higher aspect ratio of TRT plasma. For the same reason, the reversal of magnetic field shear in the pedestal occurs at a lower current density, which causes the instability of modes with low toroidal wave numbers and reduces the effect of diamagnetic stabilization.

A Possible Dust Origin for an Unusual Feature in Io’s Sodium Neutral Clouds

Abstract We report the results of model simulations performed to explain the nature of a sodium emission feature in Io Neutral Clouds. The feature was detected via high-resolution spectroscopic observations from the 3.6 m Italian telescope TNG. The emission feature is blueshifted compared to the main emission (the banana-shaped Neutral Cloud of Io) by a few tens of km s−1, and it is most prominent when Io is a few tens of degrees before eclipse behind Jupiters shadow. The feature’s morphology changes with time, indicative of a geometrical effect. We constrained its direction, velocity, and column density with a model of sodium atom trajectories under the influence of Io’s and Jupiter’s gravity, and solar radiation pressure. The model that best explains this emission feature has the atoms injected into the exosphere from the leading/sub-Jovian hemisphere of Io (45°–68° west longitude), with velocities from 50 to 90 km s−1 relative to Io. These trajectories are consistent with those of negatively charged dust grains (radius ∼10 nm) accelerated by the corotational electric field of Jupiters magnetosphere. We propose that sputtering of sodium atoms from Na-bearing molecules (NaCl and Na2SO4) in these nanodust grains is the process responsible for our emission feature. Both modeling and observational constraints provide an order-of-magnitude estimate of the sodium production rate of ∼1026 s−1. Our work provides another method to monitor the amount of material that Io is supplying to its Neutral Clouds and plasma torus.

How to create an artificial magnetosphere for Mars

If humanity is ever to consider substantial, long-term colonization of Mars, the resources needed are going to be extensive. For a long-term human presence on Mars to be established, serious thought would need to be given to terraforming the planet. One major requirement for such terraforming is having the protection of a planetary magnetic field - which Mars currently does not have. The Earth's magnetosphere helps protect the planet from the potential sterilizing effects of cosmic rays and also helps retain the atmosphere, which would otherwise by stripped by large solar storms as they pass over the planet. Mars does have small patches of remnant surface magnetic field, but these are localized in the southern hemisphere and are not of sufficient size or magnitude to protect the planet or a colony.In this article we explore comprehensively for the first time, the practical and engineering challenges that affect the feasibility of creating an artificial magnetic field capable of encompassing Mars. This includes the concerns that define the design, where to locate the magnetic field generator and possible construction strategies. The rationale here is not to justify the need for a planetary magnetosphere but to put figures on the practicalities so as to be able to weigh the pros and cons of the different engineering approaches.The optimum solution proposed is completely novel, although inspired by natural situations and fusion plasma techniques. The solution with the lowest power, assembly and mass is to create an artificial charged particle ring (similar in form to a ‘radiation belt’), around the planet possibly formed by ejecting matter from one of the moons of Mars (in a fashion similar to that which forms the Jupiter-Io plasma torus), but using electromagnetic and plasma waves to drive a net current in the ring(s) that results in an overall magnetic field.With a new era of space exploration underway, this is the time to start thinking about these new and bold future concepts and to begin filling strategic knowledge gaps. Furthermore, the principles explored here are also applicable to smaller scale objects like manned spacecraft, space stations or moon bases, which would benefit from the creation of protective mini-magnetospheres.

Morphology of the Io Plasma Torus From Juno Radio Occultations

AbstractThe jovian moon Io disperses about 1 ton/s of material in the planetary magnetosphere, mainly by sublimation of SO2 from the surface and by its intense volcanic activity. The ejected material supplies the plasma cloud surrounding Jupiter known as Io Plasma Torus (IPT). The radio communication between Juno and the Earth DSN station crosses the IPT near the closest approach. Being a dispersive medium, the IPT introduces a path delay in the signal, which can be analyzed to retrieve the density distribution of electrons. We used radio tracking data from the first 25 orbits to investigate the morphology of the IPT and its variability. We adopted a static and axisymmetric model for the electron density and we updated it including temporal and longitudinal variability. We found that our best fit model must include both variabilities, even though on average the morphology of the IPT agrees with previous analyses. Our results suggest that the density of the outer region of the IPT fluctuates over 50% the average value over a typical time scale of about 420 days.

Spatial distribution of the X-ray-emitting plasma of SS Cygni in quiescence and outburst

Abstract We present our analysis of the Suzaku data of SS Cygni (SS Cyg) from 2005 both in quiescence and outburst. A fluorescent iron Kα line bears significant information about the geometry of an X-ray-emitting hot plasma and a cold reflector, such as the surfaces of the white dwarf (WD) and the accretion disk (AD). Our reflection simulation has revealed that the X-ray-emitting hot plasma is located either very close to the WD surface in the boundary layer (BL), with an upper limit radial position of &amp;lt;1.004 times the white dwarf radius (RWD), or near the entrance of the BL where the optically thick AD is truncated at a distance of 1.14–1.27 RWD for the assumed WD mass of 1.19 M⊙ in quiescence. In the latter configuration, the plasma torus is located just above the inner edge of the AD. The result suggests that the accreting matter is heated up close to the maximum temperature immediately after the matter enters the BL. The matter probably expands precipitously at the entrance of the BL and leaves the disk plane to reach a height comparable to the radial distance of the plasma torus from the center of the WD. In outburst, on the other hand, our spectral analysis favors the picture that the optically thick disk reaches the WD surface. In addition, the plasma distributes above the disk like coronae, as suggested by a previous study, and the 90% upper limit of the coronae radial position is 1.2 RWD.

Statistical Study on Spatial Distribution and Polarization of Saturn Narrowband Emissions

Abstract The spatial distribution and polarization of Saturn narrowband (NB) emissions have been studied by using Cassini Radio and Plasma Wave Sciences data and goniopolarimetric data obtained through an inversion algorithm with a preset source located at the center of Saturn. From 2004 January 1 to 2017 September 12, NB emissions were selected automatically by a computer program and rechecked manually. The spatial distribution shows a preference for high latitude and intensity peaks in the region within 6 Saturn radii (R s ) for both 5 and 20 kHz NB emissions. 5 kHz NB emissions also show a local time preference roughly in the 18:00−22:00 sector. The Enceladus plasma torus makes it difficult for NB emissions to propagate to the low latitude regions outside the plasma torus. The extent of the low latitude regions where 5 and 20 kHz NB emissions were never observed is consistent with the corresponding plasma torus density contour in the meridional plane. 20 kHz NB emissions show a high circular polarization while 5 kHz NB emissions are less circularly polarized with V &lt; 0.6 for majority of the cases. And cases of 5 kHz NB emissions with high circular polarization are more frequently observed at high latitude especially at the northern and southern edges of the Enceladus plasma torus.

Jupiter’s X-ray aurora during UV dawn storms and injections as observed byXMM–Newton, Hubble, andHisaki

ABSTRACTWe present results from a multiwavelength observation of Jupiter’s northern aurorae, carried out simultaneously by XMM–Newton, the Hubble Space Telescope (HST), and the Hisaki satellite in 2019 September. HST images captured dawn storms and injection events in the far-ultraviolet aurora several times during the observation period. Magnetic reconnection occurring in the middle magnetosphere caused by internal drivers is thought to start the production of those features. The field lines then dipolarize, which injects hot magnetospheric plasma from the reconnection site to enter the inner magnetosphere. Hisaki observed an impulsive brightening in the dawnside Io plasma torus (IPT) during the final appearance of the dawn storms and injection events, which is evidence that a large-scale plasma injection penetrated the central IPT between 6 and 9RJ (Jupiter radii). The extreme ultraviolet aurora brightened and XMM–Newton detected an increase in the hard X-ray aurora count rate, suggesting an increase in electron precipitation. The dawn storms and injections did not change the brightness of the soft X-ray aurora and they did not ‘switch-on’ its commonly observed quasi-periodic pulsations. Spectral analysis of the X-ray aurora suggests that the precipitating ions responsible for the soft X-ray aurora were iogenic and that a power-law continuum was needed to fit the hard X-ray part of the spectra. The spectra coincident with the dawn storms and injections required two power-law continua to get good fits.