Plasma Cloud Research Articles

Self-organization of touching-target current with ac voltage in atmospheric pressure plasma jet for medical application parameters

In experiments with the cold atmospheric pressure plasma jet, the frequency of the current measured near the treated target shows a mismatch with the voltage frequency. The system including the plasma device and target organizes the plasma delivery differently with changing voltage frequency and amplitude. All electromagnetic and chemical processes near the target depend on the frequency of the plasma-target contacts. In experiments and in 2D fluid model simulations, the self-organization of touching-target current is studied for voltage frequencies of 10–50 kHz and amplitudes of 2.5–6 kV. The streamer propagation through the volumetric plasma cloud outside of discharge device and the mechanism responsible for variation of touching-target current frequency are discussed.

Ionospheric disturbance caused by artificial plasma clouds under different release conditions

The generation and evolution of artificial plasma clouds is a complicated process that is strongly dependent on the background environment and release conditions. In this paper, based on a three-dimensional two-species fluid model, the evolution characteristics of artificial plasma clouds under various release conditions were analyzed numerically. In particular, the effect of ionospheric density gradient and ambient horizontal wind field was taken into account in our simulation. The results show that an asymmetric plasma cloud structure occurs in the vertical direction when a nonuniform ionosphere is assumed. The density, volume, and expansion velocity of the artificial plasma cloud vary with the release altitude, mass, and initial ionization rate. The initial release velocity can change the cloud's movement and overall distribution. With an initial velocity perpendicular to the magnetic field, an O+ density cavity and two bumps exist. When there is an initial velocity parallel to the magnetic field, the generated plasma cloud is bulb-shaped, and only one O+ density cavity and one density bump are created. Compared to the cesium case, barium clouds expand more rapidly. Moreover, Cs+ clouds have a higher density than Ba+ clouds, and the snowplow effect of Cs+ is also stronger.

Research of Plasma Parameters Formed in the Laser Welding Area in Vacuum

The use of laser technology in the manufacturing processes of mechanical engineering is gradually increasing. However, laser welding cannot compete with electron beam welding because the processes of the interaction of the laser beam with the plasma arising above the zone of the laser beam affecting the metal are not sufficiently studied. Of particular interest is the use of laser welding in vacuum. The study of the secondary emission signal in the zone of the laser beam affecting the metal allows one to obtain information about the plasma cloud in the zone of laser welding in vacuum. To study the secondary emission current in the laser welding zone, a computer system with an analog-to-digital interface can be used. The registered secondary emission current made it possible to estimate such parameters of the plasma arising in the laser welding zone in vacuum as the plasma concentration, electron temperature, and plasma potential.

Particle acceleration by interstellar plasma shock waves in non-uniform background magnetic field

ABSTRACTParticle acceleration by plasma shock waves is investigated for a magnetized plasma cloud propagating in a non-uniform background magnetic field by means of analytical and numerical calculations. The mechanism studied here is mainly, magnetic trapping acceleration (MTA) which is previously investigated for a cloud moving through the uniform interstellar magnetic field (IMF). In this work, the acceleration is studied for a cloud moving in an antiparallel background field with spatial variations along the direction of motion. For negative variation, the cloud moves towards an antiparallel magnetic field with an increasing intensity, the trapped particle moves to locations with higher convective electric field and therefore gains more energy over time. For positive variation, the background field decreases to zero and changes into a parallel field with an increasing intensity. It is concluded that, when the background field vanishes, the MTA mechanism ceases and the particle escapes into the space. This leads to a bouncing acceleration which further increases energy of the gyrating particle. The two processes are followed by a shock drift acceleration, where due to the background magnetic field gradient, the particle drifts along the electric field and gains energy. Although for positive variation, three different mechanisms are involved, energy gain is less than in the case of a uniform background field.

Extreme intra-hour variability of the radio source J1402+5347 discovered with Apertif

The propagation of radio waves from distant compact radio sources through turbulent interstellar plasma in our Galaxy causes these sources to twinkle, a phenomenon called interstellar scintillation. Such scintillations are a unique probe of the micro-arcsecond structure of radio sources as well as of the sub-AU-scale structure of the Galactic interstellar medium. Weak scintillations (i.e. an intensity modulation of a few percent) on timescales of a few days or longer are commonly seen at centimetre wavelengths and are thought to result from the line-of-sight integrated turbulence in the interstellar plasma of the Milky Way. So far, only three sources were known that show more extreme variations, with modulations at the level of some dozen percent on timescales shorter than an hour. This requires propagation through nearby (d ≲ 10 pc) anomalously dense (ne ∼ 102 cm−3) plasma clouds. Here we report the discovery with Apertif of a source (J1402+5347) showing extreme (∼50%) and rapid variations on a timescale of just 6.5 min in the decimetre band (1.4 GHz). The spatial scintillation pattern is highly anisotropic, with a semi-minor axis of about 20 000 km. The canonical theory of refractive scintillation constrains the scattering plasma to be within the Oort cloud. The sightline to J1402+5347, however, passes unusually close to the B3 star Alkaid (η UMa) at a distance of 32 pc. If the scintillations are associated with Alkaid, then the angular size of J1402+5347 along the minor axis of the scintels must be smaller than ≈10 μas, yielding an apparent brightness temperature for an isotropic source of ≳1014 K.

Pulsar radio emission mechanism − I. On the amplification of Langmuir waves in the linear regime

ABSTRACT Observations suggest that in normal period radio pulsars, coherent curvature radiation is excited within 10${{\ \rm per\ cent}}$ of the light cylinder. The coherence is attributed to Langmuir mode instability in a relativistically streaming one-dimensional plasma flow along the open magnetic field lines. In this work, we use a hot plasma treatment to solve the hydrodynamic dispersion relation of Langmuir mode for realistic pulsar parameters. The solution involves three scenarios of two-stream instability, viz. driven by high energy beams, due to longitudinal drift that leads to a separation of electron–positron distribution functions in the secondary plasma and due to cloud–cloud interaction causing spatial overlap of two successive secondary plasma clouds. We find that sufficient amplification can be obtained only for the latter two scenarios. Our analysis shows that longitudinal drift is characterized by high growth rates only for certain multipolar surface field geometry. For these configurations, very high growth rates are obtained starting from a few tens of km from the neutron star surface, which then falls monotonically with increasing distance. For cloud–cloud overlap, growth rates become high starting only after a few hundred km from the surface, which first increases and then decreases with increasing distance. A spatial window of up to around a 1000 km above the neutron star surface has been found where large amplitude Langmuir waves can be excited while the pair plasma is dense enough to account for high brightness temperature.

Optimization of Electric Thrust Based on Pulse Arc Plasma Using Pulsed Magnetic Field

Based on the results of a numerical simulation, a possibility in principle is shown to achieve an effective magneto-induction correction of high-gradient plasma expansion from a localized arc source and a respective severalfold increase in the thrust pulse with a steepness of the induction rise in the accelerator on the order of 104 T/s. In these conditions, a pulse-periodic mode of the device operation is required with a delay of the current pulse front in the magnetic field source relative to the ignition voltage pulse in the plasma source, which is determined by the expansion velocity of the plasma cloud within the device.

Low-Frequency Whistlers Produced by Laser Plasma Clouds in a Magnetized Plasma

The limiting mode of the generation of low-frequency torsional whistlers is obtained for the first time. Laser plasma clouds create only weak whistlers in a weakly magnetized laboratory plasma (argon), allowing the whistler magnetic field to reach record values of ~25% of the background magnetic field.

Numerical simulation on the formation and merging of ablation plasma in two exploding aluminum wires

In this paper, computational results characterizing the formation and merging of counter-streaming interpenetrating plasma flows formed in exploding double parallel aluminum wires are presented. A radial magnetohydrodynamic computation is carried out first to obtain the parameters of core-corona structure in individual wires, providing an initial condition for the planar magnetohydrodynamic model in a multi-species fluids scheme with two-temperature treatment of plasma. In the XY plane, two aluminum plasma clouds are surrounded by extremely thin air, which represents a vacuum environment. A long-lasting compressed layer of extremely thin air in the central region of the inter-wire gap is formed before the merger of aluminum plasma flows. The accordance between the increasing mass fraction of aluminum plasma species in the central slit and the enhancement in self-emission light demonstrates that the real physical characteristics of extremely low-density vacuum environment plays an important role in merger of aluminum plasma flows. Current density is concentrated in the central column during the merging process of counter-streaming interpenetrating aluminum plasma flows, evolving from a structure of bifurcated current sheets into a single narrow sheet. Efficient numerical investigation on the interaction between counter-streaming plasma flows requires the incorporation of surrounding fluid species of extremely thin air.

Electromagnetic Scattering by Artificial Plasma Clouds in the Ionosphere

Vaporized samarium (Sm) has been released in the ionosphere for artificially creating plasma clouds, which may be tailored as radio wave reflectors for over-the-horizon communications. The model of samarium releases needs to be further refined for filling the gap between experimental observations and theoretical simulations. A sophisticated simulation model, so far to date, for samarium release in the ionosphere has been developed, and the redundancy reaction, inversion, and the photochemical reactions are all taken into account. The model results are consistent with experimental observations. Due to the geomagnetic field and neutral wind, the shape of artificial plasma clouds significantly changes. The error of the spherically symmetric reflection model is large. According to the density distribution of plasma clouds, the geometric theory of diffraction (GTD) is introduced here to deal with the electromagnetic scattering. The GTD-based scattering model has been established and used to study the time–space evolution of the ground-received power patterns in this article.

Generation of confined plasma balls propagating along discharge channels: A comparison with ball lightning

This work provides a tabletop analogy to thunderstorms, which allows to produce confined and luminous plasma balls. The spectral, temporal, and spatial characterizations of these plasma balls give some indications on the formation of ball lightning. The formation of these luminous plasma balls originates from the confinement and motion of plasma cloud injected into the lower pressure channel produced along the path of the discharge.

Analysis of the amplitude-time parameters of current pulses in a plasma during laser beam welding

The share of application of laser processing of materials in technological processes of mechanical engineering has increased over the past few years. In this regard, there is a need for reliable control of the technological parameters of the laser welding process. In deep penetration laser welding, part of the beam power is absorbed by the plasma cloud. As a result, a significant decrease in the penetration depth is observed. Using amplitude-time pulse of current in the plasma in the zone of impact of the laser beam on the metal is one of the directions of the work necessary for the control of the processes in the melting channel. The study of the processes of secondary emission in the plasma in the zone of impact of the laser beam on the metal allowed carrying out numerical simulation of the processes during laser welding. The models took into account the dependence on the focusing of the laser beam and other technological parameters of laser welding. The registration of the secondary emission current was also carried out in order to control the geometric parameters of penetration during laser welding. This technique can be used to build methods for the operational control of the welding process.

The Secret of the Titius-Bode Law: A New Theory on How Our Planetary System Came Into Existence

Our planetary system still has several unsolved riddles. One of them is the Titius-Bode law. With the aid of this law, it is easy to find the distances of planets from the sun. For many astronomers, this is coincidence. They argue that there is no known physical mechanism that generates a particular sequence of planets’ distances. However, if one investigates the structure of the law, it quickly becomes clear that the Titius-Bode law is directly connected with the formation of planets. Our planets did not come into existence through so-called accretion. At the beginning of its existence, the sun was presumably a T-Tauri star. These are young stars in the process of their formation. They pulsate irregularly, thereby accelerating clouds of plasma in the surrounding dust disk. Each of these eruptions thus generated a planet. This of course goes much more quickly than if they had to be formed from the dust of planetary disks. This new theory not only describes how the planets and the distances of the planets came into existence. It also gives a new description of how the moon came into existence, the cause for large moon craters, the slow rotation of Venus, the formation of the asteroid belt, the high iron content of the planet Mercury, and the sun’s loss of rotational impulse, among other things.

Comparison between ionospheric disturbances caused by barium and cesium

After being released in the ionosphere, alkali-metal atoms will be rapidly photoionized by solar UV, producing positive ions and electrons, and forming artificial plasma cloud. Based on a three-dimensional two-species fluid model, considering both the loss of barium atoms due to photoionization and oxidation and the influence of horizontal wind field in the release region, the spatial-temporal evolution of the artificial plasma cloud is discussed. By taking into account the electromagnetic field force, pressure gradient, particle collisions and ion inertia, the ionospheric disturbance effects caused by barium and cesium are compared with each other. The simulation results show that the alkali metal rapidly expands after being released in the ionosphere, and the generated plasma cloud gradually forms an ellipsoidal structure from the inside to the outside under the constraint of magnetic field with considering no wind. Meanwhile, the expanded plasma cloud pushes away the background oxygen ions, forming an oxygen ion density hole in the release center and two symmetrical density bumps on both sides. In the absence of neutral wind, the plasma cloud is dominated by the movement along magnetic field, while considering the background neutral wind, the plasma cloud and background disturbance area will move along the direction of wind, so that the density gradient of plasma cloud becomes steepening on the upwind side. Although the movement of ion cloud across the magnetic field is constrained, the neutrals can pass through the magnetic field freely, so the ion cloud and neutral cloud will separate from each other slowly. Also, the presence of horizontal wind field will make a greater disturbance to the background oxygen ion. By comparing the simulation results of barium and cesium we can see that, qualitatively, the expansion characteristics of Cs<sup>+</sup> and Ba<sup>+</sup> as well as their effects on the background O<sup>+</sup> are similar. Due to the small diffusion coefficient of cesium, the barium cloud expands more rapidly and the coverage area of Ba<sup>+</sup> cloud is wider. Because of the large photoionization rate of cesium, the ionization yield of cesium is higher than that of barium when the same mass is released. In addition, the snowplow effect of Cs<sup>+</sup> is stronger than that of Ba<sup>+</sup>, and the oxygen ion density holes and bumps caused by Cs<sup>+</sup> are also larger.

Magnetic Field Effect on Antenna Signals Induced by Dust Particle Impacts

AbstractThe Radio and Plasma Wave Science instrument on Cassini has observed fewer than expected dust particle impacts during the mission's Grand Finale orbits. The relatively strong magnetic field in the close vicinity of the planet has been suggested to affect the intensity of the dust impact generated signals. A laboratory investigation is performed using dust particles accelerated to ≥20 km/s speed impacting onto a previously developed model of the spacecraft and the Radio and Plasma Wave Science antennas. The external magnetic field is generated by two sets of magnetic coils. The recorded antenna waveforms are decomposed into contributions from the electrons and ions of the dust impact generated plasma cloud. A good qualitative understanding of the waveforms is achieved by dividing the electron and ion population into two portions: one that is escaping from the spacecraft and another that is collected by the spacecraft. The experimental results show that the part of the signal corresponding to escaping electrons is affected by the magnetic field and that dust impact signals can be significantly reduced for spacecraft floating potentials close to zero.

Low-frequency waves produced by a package of laser plasma clouds in a magnetized background

It was shown for the first time that in a laboratory experiment a train of laser plasma clouds makes it possible to increase the length of the whistler waves generated in the power tube of a magnetized medium. The intensity of waves is orders of magnitude higher than the level achieved by known methods.

Relationship Between Scattering and Dispersion Measure of the Crab Nebula Pulsar

The correlation between scattering and the dispersion measure of the Crab Nebula pulsar B0531+21, obtained earlier from observations made on the Large Phased Array (LPA) at 111 MHz and at Jodrell Bank Observatory, has been confirmed using new independent measurements at the Pushchino Radio Astronomy Observatory and Jodrell Bank. The scattering varies in the range 10–115 ms, and can be explained by the passage of clouds of plasma in the nebula with sizes 1011–1012 m, electron densities ne = 103–104 cm−3, and various degrees of turbulence in front of the pulsar. During a relatively quiescent period in 2002–2007, the turbulence coefficient in the direction of the Crab Nebula pulsar was found to be C2n = 0.00661 m−7, and the mean density variations in the Crab Nebula to be Δne ~ 0.02 cm−3, ne ~ 2 cm−3, so that Δne/ne ~ 0.01. In the comparatively active period 2009–2013, C2n = 0.0662 m−7, ne ~ 2 cm−3, Δne ~ 0.06 cm−3, and Δne/ne ~ 0.03.

Diamagnetic Plasma Clouds in the Near Lunar Wake Observed by ARTEMIS

Abstract Because of the plasma pressure gradient across the lunar wake boundary, the interplanetary magnetic field is enhanced in the lunar wake. In previous works, the solar wind ions that enter into the near lunar wake are found to have an unimportant influence on the magnetic field within the lunar wake. In this study, two cases of a 22%–70% reduction of the magnetic field in the near lunar wake are first observed by the Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon’s Interaction with the Sun mission (ARTEMIS). The magnetic field depressions are caused by the refilling of dense plasma clouds (with densities of 0.20–0.47 cm−3) into the near lunar wake. The ions of the plasma clouds that originate from the reflected solar wind ions in the lunar dayside are accelerated into the near lunar wake by the solar wind convection electric field. The source regions of the reflected ions can be traced back to the lunar magnetic anomalies over the sunlit surface. Pressure (magnetic pressure + thermal pressure) balances are roughly maintained for both cases at the boundary between the plasma cloud and the ambient plasma. Our results imply that the interaction between the solar wind and lunar magnetic anomalies drastically disturbs the near-Moon electromagnetic environment.

The motion and distribution of the gas in the central 300 pc of the galaxy as revealed by spectra of H3.

Spectroscopy of absorption lines of H3+ in the central molecular zone (CMZ) of the Galaxy show that a previously largely unknown component of the interstellar medium there, warm (T∼200 K) and diffuse (n ≲ 102 cm-3) gas, makes up a large fraction of the volume of the CMZ, and that this gas is moving radially outward from the centre. These discoveries upend the generally accepted understanding that the interstellar environment of the CMZ comprises almost entirely an ultra-hot plasma and dense molecular clouds. The radial momentum associated with the diffuse gas in the CMZ exceeds that of the ejecta of thousands of core-collapse supernovae and implies some extraordinary past activity in the centre, possibly associated with the supermassive black hole, Sgr A*. We speculate that within approximately 106 years, gravity could halt the expansion of the diffuse gas and that contraction towards the centre could then commence. This article is part of a discussion meeting issue 'Advances in hydrogen molecular ions: H3+, H5+ and beyond'.

Моделирование развития экваториальных плазменных пузырей из плазменных облаков

В работе определяются и изучаются два параметра процесса развития экваториальных плазменных пузырей (ЭПП): максимальная скорость внутри ЭПП и время развития ЭПП. Исследования проводятся для случаев, когда ЭПП возникают из одной, двух или трех зон повышенной концентрации, или начальных плазменных облаков. Механизмом развития ЭПП является неустойчивость Релея–Тэйлора (НРТ). Ранее было выяснено, что время начальной стадии развития ЭПП должно уложиться в интервал времени, благоприятный для формирования ЭПП (в этом случае линейный инкремент нарастания больше нуля). Этот интервал укладывается для экваториальной ионосферы Земли в промежуток от 3000 с до 7000 с.