Plasma Ejection Research Articles

Effects of bias magnetic field on plasma ejection and dynamic characteristics of a coaxial gun operated in gas-puffed mode

The effects of bias magnetic field on the discharge characteristics of a coaxial gun and the parameters of ejected plasma are studied. At constant initial conditions (charging voltage, gas-puffed), magnetic probe data at different axial positions reveal the influence of the external bias magnetic field on the current distribution within the annular flow channel. Both photodiode signals and plasma radiation images show the plasma ejection characteristics. It is found that either applying or not applying the bias magnetic field results in two types of plasma with distinct ejection characteristics: spheromak or jet. By comparing the plasma parameters with and without bias magnetic field, it is found that the variation of jets velocity and momentum with discharge conditions are consistent with the snowplow model, whereas the spheromak plasma is subjected to a retarding force during the ejection, which decelerates the spheromak. Irrespective of the bias magnetic field, an increase in the discharge current amplitude leads to an elevation in electron density and temperature. The density of the spheromak is lower than that of the jet, but the temperature is higher. This is due to the fact that the electromagnetic focusing mechanism in the jet leads to a further increase in density, while the magnetic field lines stretched during the formation of the spheromak inhibit the focusing effect and expand freely after ejection. In addition, the magnetic field stretching process consumes part of the axial kinetic energy from the plasma and converts it into magnetic energy. The subsequent magnetic reconnection event causes the magnetic energy to be dissipated resistively by heating the plasma and then be converted into thermal energy. These results give us a better understanding in the interaction between plasma and magnetic field.

Spectro-temporal Studies of Rapid Transition of the Quasi-periodic Oscillations in the Black Hole Source H1743-322

Abstract An appearance or disappearance of quasi-periodic oscillations (QPOs) associated with the variation of X-ray flux can be used to decipher the accretion–ejection mechanism of black hole X-ray sources. We searched for and studied such rapid transitions in H1743-322 using archival data from the Rossi X-ray Timing Explorer and found eight such events, where a QPO vanishes suddenly along with the variation of X-ray flux. The appearance/disappearance of QPOs was associated with four events exhibiting type-B QPOs at ∼4.5 Hz: one was a type-A QPO at ν ∼ 3.5 Hz, and the other three were connected to type-C QPOs at ∼9.5 Hz. Spectral studies of the data revealed that the inner disk radius remained at the same location around 2–9 r g , depending on the model used, but power-law indices were varying, indicating that either a corona or a jet is responsible for the events. The probable ejection radii of coronas were estimated to be around 4.2–15.4 r g based on the plasma ejection model. Our X-ray and quasi-simultaneous radio correlation studies suggest that the type-B QPOs are probably related to the precession of a weak jet, though a small and weak corona is present at its base, and the type-C QPOs are associated with the base of a relatively strong jet, which is acting like a corona.

Hard X-ray selected giant radio galaxies – III. The LOFAR view

ABSTRACT Giant radio galaxies (GRGs), with extended structures reaching hundreds of kpc, are among the most spectacular examples of ejection of relativistic plasma from supermassive black holes. In this work, third of a series, we present Low-Frequency Array (LOFAR) images at 144 MHz, collected in the framework of the LOFAR Two-metre Sky Survey Data Release 2 (LoTSS DR2), for nine sources extracted from our sample of hard X-ray-selected GRGs (HXGRGs, i.e. from INTEGRAL/Imager on-Board the INTEGRAL Satellite and Swift/Burst Alert Telescope catalogues at >20 keV). Thanks to the resolution and sensitivity of LoTSS, we could probe the complex morphology of these GRGs, unveiling cases with diffuse (Mpc-scale) remnant emission, presence of faint off-axis wings, or a misaligned inner jet. In particular, for one source (B2 1144+35B), we could clearly detect a ∼300 kpc wide off-axis emission, in addition to an inner jet whose orientation is not aligned with the lobes axis. For another source (J1153.9+5848), a structure consistent with jet precession was revealed, appearing as an X-shaped morphology with relic lobes having an extension larger than the present ones, and with a different axis orientation. From an environment analysis, we found two sources showing an overdensity of cosmological neighbours, and a correspondent association with a galaxy cluster from catalogues. Finally, a comparison with radio-selected GRGs from LoTSS DR1 suggested that, on average, HXGRGs can grow to larger extents. These results highlight the importance of deep low-frequency observations to probe the evolution of radio galaxies, and ultimately estimate the duty cycle of their jets.

Observation and modelling of solar jets.

The solar atmosphere is full of complicated transients manifesting the reconfiguration of the solar magnetic field and plasma. Solar jets represent collimated, beam-like plasma ejections; they are ubiquitous in the solar atmosphere and important for our understanding of solar activities at different scales, the magnetic reconnection process, particle acceleration, coronal heating, solar wind acceleration, as well as other related phenomena. Recent high-spatio-temporal-resolution, wide-temperature coverage and spectroscopic and stereoscopic observations taken by ground-based and space-borne solar telescopes have revealed many valuable new clues to restrict the development of theoretical models. This review aims at providing the reader with the main observational characteristics of solar jets, physical interpretations and models, as well as unsolved outstanding questions in future studies.

Atherogenic index of plasma and left ventricular ejection fraction in newly diagnosed type 2 diabetes mellitus patients

Background: Atherogenic index of plasma (AIP), a logarithm of ratio of triglycerides and high-density lipoprotein-cholesterol is associated with the risk of cardiovascular diseases. The cardiovascular complication in Type 2 diabetes is often assessed by the left ventricular ejection fraction (LVEF). Aim: This study aimed to observe and to find any correlation between LVEF and AIP in newly diagnosed Type 2 diabetes mellitus patients. Materials and Methods: In this cross-sectional observational study, we recruited 140 (male 81, female 59) newly diagnosed Type 2 diabetes mellitus patients from a tertiary care hospital. Plasma lipids were measured from venous blood after 12-h fasting. The LVEF was measured by echocardiography. Data were presented as mean, standard deviation, and statistically tested by Chi-square and Pearson correlation coefficient in IBM SPSS Statistics 20. Results: The mean age of the participants was 53.95 ± 11.63 years (male 53.85 ± 11.12 years, female 54.08 ± 12.39 years, unpaired t-test P = 0.91). The mean LVEF was 0.59 ± 0.06 and 0.6 ± 0.05 (unpaired t-test P = 0.17) in males and females, respectively. The AIP was 0.57 ± 0.07 and 0.57 ± 0.07 (unpaired t-test P = 0.97) in males and females, respectively. There was a negative correlation (r = −0.56, P

Evaluating the Performance of a Plasma Analyzer for a Space Weather Monitor Mission Concept

AbstractWe use historical analysis of solar wind plasma and coronal mass ejections to define the range of performance required for an ion analyzer for future space weather monitoring missions. We adopt the design of a top hat electrostatic analyzer, capable of measuring the plasma protons and constructing their three‐dimensional distribution functions. The design is based on previous heritage instruments and allows monitoring of extreme space weather events. In order to evaluate the future observations and their analysis methods, we model the expected response of the instrument in simulated plasma conditions. We evaluate a novel analysis method which can determine on board the plasma bulk properties, such as density, velocity, and temperature from the statistical moments of the observed velocity distribution functions of the plasma particles. We quantify the accuracy of the derived parameters critical for space weather purposes, by comparing them with the corresponding input solar wind parameters. In order to validate the instrument design, we examine the accuracy over the entire range of the input parameters we expect to observe in solar wind, from benign to extreme space weather conditions. We also use realistic parameters of fast solar wind streams and interplanetary coronal mass ejections as measured by the Advanced Composition Explorer spacecraft, to investigate the performance of the example instrument and the accuracy of the analysis. We discuss the achieved accuracy and its relevance to space weather monitoring concepts. We address sources of significant errors, and we demonstrate potential improvements by using a fitting analysis method to derive the results.

On the Possibility of Heating the Solar Corona by Heat Fluxes from Coronal Magnetic Structures

We estimate the role of heat flux from hot magnetic loops and open flux tubes into the surrounding corona as a possible source of heating of the corona. We show that hot magnetic-flux tubes (Type-II spicules) provide a more efficient source of coronal heating than hot magnetic loops, as the closed magnetic structure of a loop substantially restricts the heat flux into the corona. In order to compensate for radiation and thermal-conduction losses, approximately $10^{4}$ Type-II spicules with a temperature of several million Kelvin are required, which is about 1% of the number of spicules simultaneously observed on the solar disk. Our analysis shows that the principal source of energy that heats the coronal plasma is photospheric convection, which generates electric currents of about $10^{10}$ – $10^{12}$ A in magnetic loops and spicules. Dissipation of the currents increases significantly in the partially ionized plasma, i.e. when ion–atom collisions and the associated Cowling conductivity occur. This results in two important effects: heating of plasma in magnetic structures up to several million Kelvin, and ejection of hot plasma from open magnetic-flux tubes to the corona, replenishing the corona with hot plasma. The ejection of hot plasma results from the heating of the spicule foot-point by electric-current dissipation, which grows with a sporadic increase in the velocity of photospheric convection, for example, due to five-minute oscillations or the Rayleigh–Taylor instability. As a result, the rate of heating the photospheric foot-points of the spicules by ring currents exceeds radiation losses, which leads to a jump in the pressure gradient and the ejection of hot plasma into the corona from the open tips of the magnetic-flux tubes.

Thermal conduction effects on formation of chromospheric solar tadpole-like jets

ABSTRACT We measure the effects of non-isotropic thermal conduction on generation of solar chromospheric jets through numerical simulations carried out with the use of one fluid magnetohydrodynamics (MHD) code magnus. Following the work of Srivastava et al. (2018), we consider the atmospheric state with a realistic temperature model and generate the ejection of plasma through a gas pressure driver operating in the top chromosphere. We consider the magnetic field mimicking a flux tube and perform parametric studies by varying the magnetic field strength and the amplitude of the driver. We find that in the case of thermal conduction the triggered jets exhibit a considerably larger energy and mass fluxes and their shapes are more collimated and penetrate more the solar corona than for the ideal MHD equations. Low magnetic fields allow these jets to be more energetic, and larger magnetic fields decrease the enhancement of mass and energy due to the inclusion of the thermal conductivity.

Cross-field transport in detached helium plasmas in Magnum-PSI

In this study, enhanced radial transport in a volume-recombining region in detached helium plasmas in a linear device, Magnum-PSI, was investigated. By installing a reciprocating Langmuir probe, electrostatic fluctuations with high spatiotemporal resolutions were measured and analyzed. As a result, the ion-flux profile broadening in the detached state and the coherent plasma structure, which has an internal electric field in the azimuthal direction, were confirmed. By analyzing the emission intensities obtained with a fast framing camera viewing around the probe head, an enhanced fluctuation, which has an azimuthal mode number of m = 1, was found to be correlated with radial plasma ejection. This m = 1 mode rotates by the drift with the radial electric field and magnetic field and is correlated with the m = 0 mode. These two modes behave like a predator and prey; they quasi-periodically appear with about a quarter-period shift. Because the ion flux flowing into the target plate decreases when the radial transport is enhanced, this cross-field transport disperses the ion flux and decreases the maximum heat load applied to the target.

Micro-cathode arc thruster using segmented insulated anode with a slit for micro-satellite propulsion

Micro-cathode arc thruster (µCAT) is an electric propulsion device that uses metal cathode material as propellent to create plasma and ultimately produce thrust, which is suitable to serve as a propulsion system for microsatellites. In order to improve propulsion performance of the µCAT, a structure using a segmented insulated anode with a slit (SISA-µCAT), which mainly consists of a truncated-cone-shaped cathode, an insulating sleeve, a segmented anode including proximal anode and distant anode, and an anodic insulation layer with a slit, is proposed in this paper. We compare and analyze the differences in discharge characteristics, plasma generation characteristics and propulsion performance among the SISA-µCAT, a segmented exposed anode µCAT (SEA-µCAT) and the known non-segmented exposed anode µCAT (NSEA-µCAT). Study results show that when adopting the SISA-µCAT, plasma ejection performance is effectively improved by utilizing the special spatial electric field formed between segmented anode and the slit structure on the anodic insulation layer, thus improving the propulsion performance of the µCAT. During a single shot, compared with the NSEA-µCAT, peak values of generated thrust and thrust-to-power ratio are increased by 11.4 times and 10.4 times, respectively, by using the SISA-µCAT. Plasma parameters indicate that peak plasma density and propagation speed are increased by 8.2 times and 2.93 times, respectively.

Absorption of decimetre radio waves in the Earth’s high-latitude ionosphere during a geomagnetic storm in June 2015

We have analyzed the radio occultation (RO) results of ∼100 sounding sessions of the high-latitude (>65°N) lower ionosphere of the Earth’s northern hemisphere, which were carried out on 22–23 June 2015 at the GPS-frequency of 1545.42 MHz (L1 band) in the FORMOSAT-3/COSMIC experiment. Coronal plasma ejections that reached the Earth in this period provoked a class G4 magnetic storm (strong geomagnetic storm with planetary Kp-index equal to 8), which in turn caused significant ionospheric fluctuations of radio waves on the sounding paths: navigation (GPS) satellites – low-orbit (FORMOSAT-3/COSMIC) satellites. For the first time, the analysis of FORMOSAT-3/COSMIC radio frequency measurements revealed the absorption of L1 radio waves in the lower high-latitude ionosphere of the Earth. The absorption value is ∼3 dB in the range of 60-90 km and in some cases reaches ∼10 dB at altitudes from 90 to 95 km. It is shown that it is possible to obtain the absorption coefficient of GPS-frequency radio waves in the Earth’s ionosphere at these altitudes from experimental data of FORMOSAT-3/COSMIC.

Eruptive–Impulsive Homologous M-class Flares Associated with Double-decker Flux Rope Configuration in Minisigmoid of NOAA 12673

Abstract We present a multiwavelength analysis of two homologous, short-lived, impulsive flares of GOES class M1.4 and M7.3 that occurred from a very localized minisigmoid region within the active region NOAA 12673 on 2017 September 7. Both flares were associated with initial jetlike plasma ejection that for a brief amount of time moved toward the east in a collimated manner before drastically changing direction toward the southwest. Nonlinear force-free field extrapolation reveals the presence of a compact double-decker flux rope configuration in the minisigmoid region prior to the flares. A set of open field lines originating near the active region that were most likely responsible for the anomalous dynamics of the erupted plasma gave the earliest indication of an emerging coronal hole near the active region. The horizontal field distribution suggests a rapid decay of the field above the active region, implying high proneness of the flux rope system toward eruption. In view of the low coronal double-decker flux ropes and compact extreme ultraviolet brightening beneath the filament, along with associated photospheric magnetic field changes, our analysis supports the combination of initial tether-cutting reconnection and subsequent torus instability for driving the eruption.

The OH Megamaser galaxy IRAS11506−3851: an AGN and star formation revealed by multiwavelength observations

ABSTRACT We present Gemini Multi-Object Spectrograph (GMOS) Integral Field Unit (IFU), Hubble Space Telescope (HST), and Very Large Array (VLA) observations of the OH Megamaser (OHM) galaxy IRAS 11506−3851. The HST images reveal an isolated spiral galaxy and the combination with the GMOS-IFU flux distributions and VLA data allow us to identify a partial ring of star-forming regions surrounding the nucleus with a radius of ≈ 500 pc. While this ring shows starburst excitation and low velocity dispersion, the region internal to the ring shows higher excitation and velocity dispersion values, with values increasing towards its borders at ≈ 240 pc from the nucleus, resembling a projected bubble. The enhanced excitation and velocity dispersion of this bubble surrounds a 8.5-GHz radio emission structure, supporting its origin in a faint active galactic nucleus (AGN) that is mostly shocking the surrounding gas via a plasma ejection seen in radio at the present stage. This is the fourth of the 5 OHM galaxies we have studied so far (from our sample of 15 OHM) for which GMOS-IFU data indicate the presence of a previously unknown faint AGN at the nucleus, consistent with the hypothesis that OHM galaxies harbour recently triggered AGN.

Coronal Mini-jets in an Activated Solar Tornado-like Prominence

Abstract High-resolution observations from the Interface Region Imaging Spectrometer reveal the existence of a particular type of small solar jet, which arose singly or in clusters from a tornado-like prominence suspended in the corona. In this study, we perform a detailed statistical analysis of 43 selected mini-jets in the tornado event. Our results show that the mini-jets typically have (1) a projected length of 1.0–6.0 Mm, (2) a width of 0.2–1.0 Mm, (3) a lifetime of 10–50 s, (4) a velocity of 100–350 km s−1, and (5) an acceleration of 3–20 km s−2. Based on spectral diagnostics and EM-Loci analysis, these jets seem to be multithermal small-scale plasma ejections with an estimated average electron density of ∼2.4 × 1010 cm−3 and an approximate mean temperature of ∼2.6 × 105 K. Their mean kinetic energy density, thermal energy density, and dissipated magnetic field strength are roughly estimated to be ∼9 erg cm−3, 3 erg cm−3, and 16 G, respectively. The accelerations of the mini-jets, the UV and EUV brightenings at the footpoints of some mini-jets, and the activation of the host prominence suggest that the tornado mini-jets are probably created by fine-scale external or internal magnetic reconnections (a) between the prominence field and the enveloping or background field or (b) between twisted or braided flux tubes within the prominence. The observations provide insight into the geometry of such reconnection events in the corona and have implications for the structure of the prominence magnetic field and the instability that is responsible for the eruption of prominences and coronal mass ejections.

Spatiotemporal dynamics of cross-field ejection events in recombining detached plasma

Three-dimensional spatiotemporal dynamics of detached helium plasma parameters along time, radius, and magnetic field were revealed in the linear device NAGDIS-II. To measure plasma parameters before and after the radial plasma ejection that was enhanced around the volume-recombining region, the conditional averaging technique was applied. The radial ejection was found to correlate with low-frequency changes of plasma-column parameters, which seemed to suppress the axial movement of the recombining region. Moreover, an azimuthal charge separation inside the ejected structure was observed, similar to the typical edge transport phenomenon: blobby plasma transport. The neutral flow effect was suggested as a candidate of the driving force.

Analysis of plasma detachment in the magnetic thrust chamber using full particle-in-cell simulation

A magnetic nozzle, which is a convergent-divergent magnetic field to control a plasma flow, has been investigated for application to plasma propulsion systems in spaceships. In the magnetic nozzle, plasma thermal energy is converted to one-directional kinetic energy by Lorentz force to generate thrust. Although magnetic field structure and strength are optimized for improvement of the thrust performance, it is essential to understand physical processes of plasma ejection from the nozzle, because the plasma may flow back along lines of magnetic field if the directed plasma continues being strongly magnetized. It is assumed, for one of the scenarios to explain a plasma detachment, that a plasma detaches from magnetic field when a cyclotron radius exceeds a scale length of magnetic field in size. Hence, we investigate a plasma detachment condition by analyzing parameters of the plasma for unmagnetization. We assumed individual particle motion of a fully ionized plasma in the magnetic nozzle and conducted a full particle-in-cell simulation in a two-dimensional coordinate system. We calculated a ratio of cyclotron radius to a scale length of the magnetic field. The ratio increased in a downstream due to variation of magnetic field induced from a diamagnetic cavity, suggesting unmagnetization.

Design of High Voltage Pulsed Power Supply for HFRC

The HUST field-reversed configuration (HFRC) is a field reversed plasma research device based on colliding and merging under design. To increase the parameters of the initial plasma formed in the theta-pinch, the theta-pinch is designed with very high parameters, namely a chamber diameter of 0.6 m, a bias magnetic field of -0.16 T, a preionization frequency of 150 kHz, and a main magnetic field of 0.6 T. To control the plasma formation and ejection, the discharge regulating accuracy for the theta-pinch is required within several microseconds. Thus, a high voltage, high current pulsed power supply with high controllability is required to satisfy the physical design. This article mainly presents the challenges and solutions in the design of the power supply system. First, 18 theta-pinch coils are used for the field generation to reduce the current on each coil, which results in design parameters of 70 kV/86 kA for the power supply. Then, a new topology with two power supply modules connected in series is adopted to feed the coil, which reduces the system voltage level and increases the operational reliability. Besides, hydrogen thyratron is adopted as the pulsed switch, and a corresponding trigger circuit based on insulated gate bipolar transistor (IGBT) is designed to ensure the precise control of the sequential discharge. Experimental tests are also performed on the thyratron and its trigger circuit, and the breakdown delay time is proven to be less than 1 μs. In conclusion, the designed power supply system can satisfy the requirements of high operation parameters and high controllability.

Application of dynamic mode decomposition to rotating structures in detached linear plasmas

Dynamic mode decomposition (DMD) was applied to time-series snapshots of dynamic behavior in detached plasmas with a fast framing camera in the linear plasma device NAGDIS-II. The DMD extracted radial plasma ejection and Er×B rotation structures, which are associated with blob-like plasma structures. Besides, we investigated the influences from neutral gas pressure on the growth rates of the DMD modes. By increasing the neutral gas flow rate in the detached plasma, the growth rate of rotation mode became larger while the frequency decreased. The results indicated that the ejected plasma existed for a longer time in the periphery region. It is likely due to the fact that the ratio of the radial velocity to the rotation velocity of the ejected plasma decreased.

Local plasma parameter measurements in colliding laser-produced plasmas for studying magnetic reconnection

We have implemented laser Thomson scattering for local plasma measurement of electron and ion temperatures, electron density, flow velocity, and charge state. The electron density increases by two times in the interaction of two plasma flows, indicating collisionless interaction. The density and velocity show fluctuations only at t=40 ns, and the density suddenly decreases, indicating the plasma ejection from the interaction region, which can be explained by a magnetic reconnection. The electron temperature in the double-flow is larger than that in the single flow. This may be explained by the energy transfer from the plasma kinetic energy to thermal energy. The ion temperature is much larger than electron temperature in the double-flow, and this may be explained by collisional effects between two plasmas, and/or possibly interpreted as a thermalization due to magnetic reconnection.

Excitation Sources of Oscillations in Solar Coronal Loops: A Multi-wavelength Analysis

Abstract An investigation into the excitation sources of oscillations detected in a coronal loop structure is carried out using the images obtained with Interface Region Imaging Spectrometer (IRIS) and the Atmospheric Imaging Assembly (AIA) instrument on board the Solar Dynamics Observatory (SDO). A loop structure in the active region AR 11967 on 2014 January 28, oscillating in the vicinity of a strong eruption and an M3.6 class flare site, is clearly noticeable in SDO/AIA 171 Å images. We study in detail, the oscillations with detected periods between 4 and 13 minutes and their connection in IRIS SJI 1330 Å and SDO/AIA 1700 Å images; both of these wavelengths sample the lower parts of the solar atmosphere. The simultaneous presence of many oscillations in the region of interest in all three wavelength passbands suggest that these oscillations were excited in the lower-chromosphere–photosphere plasma connected to the loop structure and then propagated at higher heights. We further investigate the Doppler velocity measurements from the spectrograph snapshots in IRIS C ii 1336 Å, Si iv 1403 Å and Mg ii k 2796 Å. These show signatures of upflows in the vicinity of the loop structure’s endpoints estimated from 171 Å images. We suggest that some of the oscillations observed in AIA 171 Å have been triggered by plasma ejections and perturbations seen in the lower layers of the solar atmosphere. Based on the estimated phase speeds, the oscillations are likely to be slow magnetoacoustic in nature.