Plasma Disk Research Articles

Formation Mechanism of Fingers That Protrude Eastward From the Io Plasma Disk During the Interchange Instability

AbstractThe solar wind‐magnetosphere‐ionosphere interaction at Jupiter is reproduced numerically adopting the nine‐component magnetohydrodynamic simulation. Calculations take into account the magnetosphere‐ionosphere coupling, Jovian rotation, and Io plasma source. High‐speed rotating plasma inside restricted magnetospheric space causes expansion and contraction of magnetic field, forming super‐rotation at radial distance 20∼30 Rj and co‐rotation breakdown further outside. Field‐perpendicular current that restores co‐rotational delay beyond 30 Rj is connected via field‐aligned current to the main oval in the ionosphere. Inside 20 Rj, there is almost co‐rotation region (deviation from co‐rotation less than 20 km/s). Particularly within 10 Rj, the deviation from co‐rotation is less than 2 km/s. In the nearly co‐rotating region, the Io plasma forms a disk structure through field‐aligned redistribution. The interchange instability occurs near the outer wall of the Io plasma disk, and instability flow develops to vortex. Through this instability, a part of the centrifugal drift current supporting the Io plasma disk is connected to low‐latitude field‐aligned current that generates beads‐like spots on the lower latitude side of the main oval. Resulting interchange instability comes to satisfy the structure of convection and enables further development of vortex. The Coriolis force acting on eastward flow inside the developing vortex makes this flow protrude further outward, forming eastward bending fingers. Inside 10 Rj, Io plasma transport by the interchange instability becomes slower, despite the center of the disk. Io plasma escapes from the inner magnetosphere with a time constant of 20 days if this slow transport is taken into account.

Radial and Vertical Structures of Plasma Disk in Jupiter's Middle Magnetosphere

AbstractThe Juno mission flew through the plasma disk near the equator in Jupiter's magnetosphere frequently. We identify 274 plasma disk crossings of Juno between 10 and 40 RJ from PJ5 to PJ44. Using a forward modeling method that combines the JADE‐I time‐of‐flight and SPECIES data sets, we perform a survey of ion properties in the plasma disk. Ions are heated from 1.5 to 6 keV between 15 and 30 RJ. Density and temperature are locally anti‐correlated. Assumed to be related to centrifugal instabilities, cold, dense plasma are commonly observed near midnight. Plasma corotates around Jupiter and the rigid corotation breaks down outside 15–20 RJ. The plasma bulk velocity increases from the post‐dusk sector to the pre‐dawn sector featuring injection flows in the pre‐dawn sector, which is consistent with the Vasyliunas cycle. Strong outflows (>100 km/s) are commonly observed outside 20 RJ and the average radial velocity increases with radial distance. The ion abundance changes between 10 and 18 RJ and that might indicate plasma sources and/or sinks near Europa and Ganymede. The vertical distribution of ions is controlled by the balance between centrifugal, pressure gradient, and ambipolar electric field forces. An example near the M‐shell of 13.5 shows that average plasma temperature increases by a factor of 10 from the disk center to edge, because cold ions are more confined near the equator. Lighter ions with higher charge states have more mobility along the field line and have larger scale heights. The observations are compared with multi‐species diffusive equilibrium model.

Forward Modeling of 3‐D Ion Properties in Jupiter’s Magnetosphere Using Juno/JADE‐I Data

AbstractThe Jovian Auroral Distributions Experiment Ion sensor (JADE‐I) on NASA’s Juno mission provides in‐situ measurements of ions from 0.1 to 46.2 keV/q inside Jupiter’s magnetosphere. JADE‐I is used to study the plasma with two types of datasets from the same measurement: Time‐of‐flight (TOF) and SPECIES. The TOF dataset provides mass‐per‐charge measurements with a range of 1–64 amu/q but oversamples particles over 6π steradian viewing per spacecraft spin and has little directional information. On the other hand, the SPECIES dataset can provide a good measurement of the flow direction but does not provide mass‐per‐charge information due to the telemetry limit. In this study, we developed a 2‐step forward modeling method that combines the advantages and avoids the disadvantages of TOF and SPECIES data to derive the 3‐D properties of heavy ions. Assuming that the ion velocity distribution can be described with the kappa distribution, we first perform the forward model fit of the TOF data to calculate the relative abundance of heavy ion species. Then we fix the relative abundance and perform the second forward model fit on the SPECIES data. Using this method, we obtain the densities of different heavy ions, the shared temperature and kappa value, and the 3‐D flow velocity vector. Some data examples of the equatorial plasma disk before Perijove 24 are included to demonstrate the method. Plasma properties can then be mapped to explore spatial and temporal variabilities in Jupiter’s magnetosphere.

A Self‐Consistent Model of Radial Transport in the Magnetodisks of Gas Giants Including Interhemispheric Asymmetries

AbstractOutward transport of plasma in the inner and middle magnetospheres of gas giants results from an interplay between mass loading from the inner dominant mass sources (volcanic moons), flux tube interchange in the centrifugally unstable magnetospheric plasma disk, turbulent heating of the plasma, and coupling between the equatorial plasma and the planetary upper atmosphere through magnetic field‐aligned current loops and/or Alfvén waves. We present a new analytical formalism describing large scale transport in gas giant systems, combining two historical approaches: radial diffusion of mass and energy through flux tube interchange, and angular momentum transport through corotation enforcement. Under the hypotheses of axisymmetry, steady‐state, and multi‐fluid plasma, we provide transport equations for total contents of flux tubes. They feature new transport parameters accounting for the latitudinal extent of the disk, and self‐consistently include field‐aligned potential drops in the magnetosphere‐ionosphere coupling. Our general formalism has a wealth of applications, two of which are presented, corresponding to the cases of the two gas giants: the effect of interhemispheric asymmetries in the resistive and magnetic properties between the northern and southern ionospheres on the transport of angular momentum at Jupiter, and the influence of the plasma disk thickness on transport at Saturn. We apply our formalism to derive ionospheric parameters and reproduce the Juno and Cassini data. Further work will allow for more complete numerical solutions of our equations, with the aim of capturing the broad complexity of fast rotating magnetospheric systems which can be found inside and outside the Solar System.

Plasma Observations During the 7 June 2021 Ganymede Flyby From the Jovian Auroral Distributions Experiment (JADE) on Juno

AbstractWe report on plasma observations from Juno/Jovian Auroral Distributions Experiment during the Ganymede flyby on 7 June 2021. Juno approached Ganymede from southern latitudes, passed through the wake region, then through its magnetosphere to closest approach (1,046 km from the surface) on the night side, and then back into Jupiter's plasma disk. We describe general plasma properties in the regions explored along the trajectory. We infer that Juno traversed a region of open field lines where one end intercepts Ganymede and the other Jupiter. The observations do not support Juno crossing into the closed field line region. The ion composition near Ganymede is very different than that of the nearby plasma environment. H2+ and H3+ ions were detected near Ganymede and in the wake region. Low energy (∼0.1–1 keV) electrons are enhanced just outside the magnetopause, in the wake (inbound trajectory) and in the magnetopause boundary layer (outbound trajectory).

The Impact of Black Radiation on the Jeans Gravitational Instability Criterion in a Circumstellar Plasma Disk in View of Nonisentropic Effects

The Impact of Black Radiation on the Jeans Gravitational Instability Criterion in a Circumstellar Plasma Disk in View of Nonisentropic Effects

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.

Research progress on the seed plasma disk magnetohydrodynamic generator

To fully and clearly understand the development status and key research problems of the seed plasma disk magnetohydrodynamic (MHD) generator, this study reviews the development process of the seed plasma disk MHD generator. The development of the disk MHD generator has experienced the stages of suppressing the ionization instability of nonequilibrium plasma, revealing the characteristics of stable nonequilibrium plasma based on the concept of seed full ionization, and proving the high performance of the disk MHD generator. At present, there are attempts to use a small area ratio disk MHD generator to obtain a high entropy efficiency at a high enthalpy extraction rate with cesium added inert gas as the working fluid. Moreover, the research progress is described from two aspects of numerical simulation and experimental research, and the key technologies and problems to be solved and the development prospects of the seed plasma disk MHD generator are analysed. It is shown that the future theoretical research still will be focused on the generation and ionization process of nonequilibrium plasma. The key technology in the future is still aimed to obtain high-quality, uniform and stable non-equilibrium plasma. Therefore, in the future, it is expected to become a high-power static power supply with a compact structure and high-power conversion efficiency. Tables 2, Figs 9, Refs 153.

Observation of Zeeman splitting effect in a laser-driven coil

The Zeeman splitting effect is observed in a strong magnetic field generated by a laser-driven coil. The expanding plasma from the coil wire surface is concentrated at the coil center and interacts with the simultaneously generated magnetic field. The Cu I spectral lines at wavelengths of 510.5541, 515.3235, and 521.8202 nm are detected and analyzed. The splittings of spectral lines are used to estimate the magnetic field strength at the coil center as ∼31.4 ± 15.7 T at a laser intensity of ∼5.6 × 1015 W/cm2, which agrees well with measurements using a B-dot probe. Some other plasma parameters of the central plasma disk are also studied. The temperature is evaluated from the Cu I spectral line intensity ratio, while the electron density is estimated from the Stark broadening effect.

Роль черного излучения в модификации критериев неустойчивости Джинса для экзопланетного пылевого плазменного диска при учете магнитной вязкости и лучевого теплообмена

Within the framework of the problem of modeling the evolution of an exoplanetary disk, the influence of blackbody radiation on the Jeans magneto-gravitational instability for a self-gravitating plasma disk is discussed, taking into account the influence on the critical length of the disturbing wave of rotation, magnetic field, dissipative processes of viscosity and thermal conductivity, as well as radiation pressure and radiation heat loss. Using the analysis of the normal mode, the general dispersion relation is derived. On its basis, modified criteria for the Jeans instability were obtained for a number of special cases associated with different relative orientations of the magnetic field, the axis of rotation, and the propagation vector of the disturbance wave. The stability of the environment is discussed using the Hurwitz criterion. Both in the case of longitudinal and transverse directions of propagation of the disturbance wave, the Jeans instability criterion is modified due to the presence of radiation heat losses and Stokes correction. The results obtained are aimed at solving the problem associated with the instability of exoplanetary accretion disks and with the formation of exoplanets.

Cassini‐Plasma Interaction Simulations Revealing the Cassini Ion Wake Characteristics: Implications for In‐Situ Data Analyses and Ion Temperature Estimates

AbstractWe have used Spacecraft Plasma Interaction Software (SPIS) simulations to study the characteristics (i.e., dimensions, ion depletion, and evolution with the changing spacecraft attitude) of the Cassini ion wake. We focus on two regions, the plasma disk at 4.5–4.7 RS, where the most prominent wake structure will be formed, and at 7.6 RS, close to the maximum distance at which a wake structure can be detected in the Cassini Langmuir probe (LP) data. This study also reveals how the ion wake and the spacecraft plasma interaction have impacted the Cassini LP measurements in the studied environments, for example, with a strong decrease in the measured ion density but with minor interference from the photoelectrons and secondary electrons originating from the spacecraft. The simulated ion densities and spacecraft potentials are in very good agreement with the LP measurements. This shows that SPIS is an excellent tool to use for analyses of LP data, when spacecraft material properties and environmental parameters are known and used correctly. The simulation results are also used to put constraints on the ion temperature estimates in the inner magnetosphere of Saturn. The best agreement between the simulated and measured ion density is obtained using an ion temperature of 8 eV at ∼4.6 RS. This study also shows that SPIS simulations can be used in order to better constrain plasma parameters in regions where accurate measurements are not available.

Survey of Juno Observations in Jupiter's Plasma Disk: Density

AbstractWe explore the variation in plasma conditions through the middle magnetosphere of Jupiter with latitude and radial distance using Juno‐JADE measurements of plasma density (electrons, protons, sulfur, and oxygen ions) surveyed on Orbits 5–26 between March 2017 and April 2020. On most orbits, the densities exhibit regular behavior, mapping out a disk between 10 and 50 RJ (Jovian radii). In the disk, the heavy ions are confined close to the centrifugal equator which oscillates relative to the spacecraft due to the ∼10° tilt of Jupiter's magnetic dipole. Exploring each crossing of the plasma disk shows there are some occasions where the density profiles are smooth and well‐defined. At other times, small‐scale structures suggest temporal and/or spatial variabilities. There are some exceptional orbits where the outer regions (30–50 RJ) of the plasma disk show uniform depletion, perhaps due to enhanced ejection of plasmoids down the magnetotail, possibly triggered by solar wind compression events.

Global Simulation of the Jovian Magnetosphere: Transitional Structure From the Io Plasma Disk to the Plasma Sheet

AbstractJupiter has a strong magnetic field, and a huge magnetosphere is formed through the solar wind‐Jupiter interaction. The generated magnetosphere–ionosphere system is reproduced based on the 9‐component Magnetohydrodynamics (MHD) and the current conservation in the ionosphere. Assuming Io plasma emission rate 1.4 t/sec, this paper reproduces self‐consistently global magnetic configuration, generations of the field‐aligned current (FAC) and aurora, formation of the Io plasma disk at 8–20 RJ, plasma corotation, instability in the plasma disk, transition from the Io plasma disk to the plasma sheet at 20–150 RJ, and the plasmoid ejection. The rotating Io plasma in the disk forms instabilities that promotes radial diffusion. H+ is supplied from the ionosphere along high‐latitude magnetic field lines and mixed with heavy ions around 15–20 RJ. Beyond 20 RJ, mixed plasma diffuses further outward by the centrifugal force that can exceed magnetic tension. In the ionosphere, the main oval occurs at 13.7°–15.5° colatitude. The Io disk is inner side of magnetic field lines traced from the low‐latitude edge of the main oval. Along magnetic field lines, the main oval is mapped from the outer edge of the Io disk to the entire plasma sheet accompanying rotation delay. Due to the corotation limit, convection is accompanied by plasmoid ejection. Back reaction of plasmoid ejection affects even transport process in the Io disk. The downward FAC occurs in the polar cap showing variability. The region of externally driven Dungey convection seems quite narrow.

Low-frequency monitoring of flare star binary CR Draconis: long-term electron-cyclotron maser emission

Recently detected coherent low-frequency radio emission from M dwarf systems shares phenomenological similarities with emission produced by magnetospheric processes from the gas giant planets of our Solar System. Such beamed electron-cyclotron maser emission can be driven by a star-planet interaction or a breakdown in co-rotation between a rotating plasma disk and a stellar magnetosphere. Both models suggest that the radio emission could be periodic. Here we present the longest low-frequency interferometric monitoring campaign of an M dwarf system, composed of twenty-one ≈8 h epochs taken in two series of observing blocks separated by a year. We achieved a total on-source time of 6.5 days. We show that the M dwarf binary CR Draconis has a low-frequency 3σ detection rate of 90−8+5% when a noise floor of ≈0.1 mJy is reached, with a median flux density of 0.92 mJy, consistent circularly polarised handedness, and a median circularly polarised fraction of 66%. We resolve three bright radio bursts in dynamic spectra, revealing the brightest is elliptically polarised, confined to 4 MHz of bandwidth centred on 170 MHz, and reaches a flux density of 205 mJy. The burst structure is mottled, indicating it consists of unresolved sub-bursts. Such a structure shares a striking resemblance with the low-frequency emission from Jupiter. We suggest the near-constant detection of high brightness temperature, highly-circularly-polarised radiation that has a consistent circular polarisation handedness implies the emission is produced via the electron-cyclotron maser instability. Optical photometric data reveal the system has a rotation period of 1.984 ± 0.003 days. We observe no periodicity in the radio data, but the sampling of our radio observations produces a window function that would hide the near two-day signal.

General features of the linear crystalline morphology of accretion disks

In this paper, we analyze the so-called Master Equation of the linear backreaction of a plasma disk in the central object magnetic field, when small scale ripples are considered. This study allows to single out two relevant physical properties of the linear disk backreaction: (i) the appearance of a vertical growth of the magnetic flux perturbations; (ii) the emergence of sequence of magnetic field O-points, crucial for the triggering of local plasma instabilities. We first analyze a general Fourier approach to the solution of the addressed linear partial differential problem. This technique allows to show how the vertical gradient of the backreaction is, in general, inverted with respect to the background one. Instead, the fundamental harmonic solution constitutes a specific exception for which the background and the perturbed profiles are both decaying. Then, we study the linear partial differential system from the point of view of a general variable separation method. The obtained profile describes the crystalline behavior of the disk. Using a simple rescaling, the governing equation is reduced to the second-order differential Whittaker equation. The zeros of the radial magnetic field are found by using the solution written in terms Kummer functions. The possible implications of the obtained morphology of the disk magnetic profile are then discussed in view of the jet formation.Graphic

Polar Flattening of Jupiter's Magnetosphere

AbstractJupiter's magnetosphere is filled with plasma that expands from Io into an equatorial plasma disk, which preferentially inflates the magnetosphere against the solar wind equatorially. This results in a polar flattened magnetosphere and changes the dynamics between the solar wind and the magnetopause boundary. The degree of polar flattening at Jupiter, however, is not well known because no spacecraft has traversed the magnetopause at high latitudes. Instead, estimates must be made from much lower latitudes. In this study, we present a new method of estimating the large‐scale shape of magnetospheres by using magnetic field draping within the magnetosheath. Utilizing data of Jupiter's dawn magnetosheath from the Juno spacecraft, we estimate the ratio of the semimajor to semiminor axes of the Jupiter‐Sun‐North Y‐Z elliptical cross section of Jupiter's magnetopause is 1.29 ± 0.29.

Distinct Accretion Modes of Cygnus X-1 Revealed from Hard X-Rays

Abstract Thanks to recurrent observations of the black hole binary Cyg X-1 carried out over 15 years the INTEGRAL satellite has collected the largest data set in the hard X-ray band for this source. We have analyzed these data, complemented by data collected by other X-ray satellites and radio flux at 15 GHz. To characterize the spectral and variability properties of the system we have examined parameters such as the hard X-ray flux, photon index, and fractional variability. Our main result is that the 2D distribution of the photon index and flux determined for the 22–100 keV band forms six clusters. This result, interpreted within the Comptonization scenario as the dominant process responsible for the hard X-ray emission, leads to a conclusion that the hot plasma in Cyg X-1 takes the form of six specific geometries. The distinct character of each of these plasma states is reinforced by their different X-ray and radio variability patterns. In particular, the hardest and softest plasma states show no short-term flux–photon index correlation typical for the four other states, implying a lack of interaction between the plasma and accretion disk. The system evolves between these two extreme states, with the spectral slope regulated by a variable cooling of the plasma by the disk photons.

Can the magneto rotational instability be performed in the presence of strong magnetic field?

According to previous studies, it is known that Magneto-Rotational-Instability (MRI) can produce turbulent in accretion disks and it can be the origin of viscosity in these systems. These studies showed that MRI can not perform in systems with strong magnetic field. So, the origin of viscosity is as open question in accretion disks with strong magnetic field yet. In this paper, we try to review the instability of accretion plasma disks in the presence of the term including electron pressure in Ohm law. This term can be important in the inner region of accretion disks where the temperature is high and density is low. Some additional terms such as time dependent electrical field and Nernst coefficients are added to equations also. Noted, these terms are neglected in previous studies. Then, the local instability analysis is applied and solutions show that the presence of electron pressure term in Ohm law, can affect the stability of system. According to results, in a system with strong magnetic field \((\beta \leq 0.1)\) and without this term, \((A=0)\), the growth rate of MRI mode is so small, \(\gamma <0.2\). This result is same as previous result and means that MRI can not perform in accretion systems with strong magnetic field. However, in the presence of this term, \(A\neq 0\), result becomes difference. Low \(A\) parameter, \(A\leq 0.12\), can decrease the growth rate of unstable mode to zero and leads to more stability in system. On the other hands, big one, \(A\succeq 0.2\) increases the growth rate of unstable mode and leads to more instability in system. So, a system with strong magnetic field, (\(\beta =0.1\)) can be unstable, \(\gamma =0.7\), when the fraction of electron pressure term in Ohm law is big, \(A=0.9\). These results show that the MRI can be amplified by electron pressure in the inner part of accretion disks and so a system with strong magnetic field can be magneto rotationally unstable in the presence of big electron pressure.

Relation between etching profile and voltage–current shape of sintered SiC etching by atmospheric pressure plasma

Sintered silicon carbide (SiC) was etched by a dielectric barrier discharge source. A high voltage bipolar pulse was used with helium gas for the plasma generation. One stable filament plasma was generated and could be used for SiC etching. As the processing gas (NF3) mixing rate increased, the width and depth of the etching profile became narrower and deeper. The differentiated V–Q Lissajous method was used for measuring the capacitances (Ceq) of the electrode after the plasma turned on. The width of the etching profile was proportional to Ceq. As the current peak value Ismx of the substrate current increased, the volume removal rate of SiC increased. The etch depth was proportional to the ratio of Ismx to Ceq. Additionally, because of the different characteristics of the plasma disks on SiC substrate by the voltage polarity, the etching profile was unstable. However, in high NF3 mixing process, the etching profile became stable and deeper.

Optimal Parameters for Intervertebral Disk Resection Using Aqua-Plasma Beams.

A minimally invasive procedure for intervertebral disk resection using plasma beams has been developed. Conventional parameters for the plasma procedure such as voltage and tip speed mainly rely on the surgeon's personal experience, without adequate evidence from experiments. Our objective was to determine the optimal parameters for plasma disk resection. Rate of ablation was measured at different procedural tip speeds and voltages using porcine nucleus pulposi. The amount of heat formation during experimental conditions was also measured to evaluate the thermal safety of the plasma procedure. The ablation rate increased at slower procedural speeds and higher voltages. However, for thermal safety, the optimal parameters for plasma procedures with minimal tissue damage were an electrical output of 280 volts root-mean-square (Vrms) and a procedural tip speed of 2.5 mm/s. Our findings provide useful information for an effective and safe plasma procedure for disk resection in a clinical setting.