共查询到20条相似文献，搜索用时 531 毫秒
1.
C. D. Gregory A. D. Ash D. M. Chambers C. Courtois R. A. D. Grundy N. C. Woolsey 《Astrophysics and Space Science》2005,298(1-2):389-393
Presented are interferometric results of the interaction of two plasmas without and with a magnetic field. This study is based
on the collision-free interaction of two millimetre-scale, counter-streaming plasmas – a proposed experimental simulation
of shock production in a supernova remnant. This collision-free interaction is compared with a separate set of experiments
with an external 7.5 T magnetic field applied. The interaction dynamics are inferred from spatially and temporally resolved
electron density measurements, and the effect of the magnetic field on the plasma interaction is discussed. 相似文献
2.
Vladimir A. Osherovich 《Astrophysics and Space Science》1982,86(2):453-469
One procedure for solving MHD equations is to search for a solution in an area that is restricted by boundary surfaces. This procedure requires the magnetic field to be truncated on the boundary. As a result, boundary current sheets appear. This approach is certainly acceptable for laboratory plasma experiments in which these surfaces are made of metal. For astrophysically relevant plasma, an alternative approach has been formulated by the author. We require the total magnetic energy,W, to be finite and, simultaneously, the magnetic fieldB to be continuous. The proposed approach leads to an eigenvalue problem that is treated analytically. The complete set of exact MHD solutions with multi-toroidal structure is obtained. These solutions are applied to coronal loops and transients, using the similarity assumption for time-dependent solutions.The derived pressure and density excess distributions are discussed. The estimation of the total mass excess, as well as the minimum value of the magnetic field intensity, is demonstrated. An indirect way of obtaining magnetic field measurements for transients, based on the developed model, is proposed. 相似文献
3.
P. A. Sturrock P. J. Baum J. M. Beckers C. E. Newman E. R. Priest H. Rosenberg D. F. Smith D. G. Wentzel 《Solar physics》1976,46(2):411-431
This report summarizes the proceedings of a meeting held on 17–20 September 1974, at Stanford University. The purpose was to explore plasma physics problems which arise in the study of solar physics. Sessions were concerned with specific questions including the following: Is the solar plasma thermal or non-thermal? What spectroscopic data are required? What types of magnetic field structures exist? Do MHD instabilities occur? Do resistive or non-MHD instabilities occur? What mechanisms of particle acceleration have been proposed? What information do we have concerning shock waves? Very few questions were answered categorically but, for each question, there was discussion concerning the observational evidence, theoretical analyses, and existing or potential laboratory and numerical experiments. 相似文献
4.
The Viking missions to Mars failed to detect any organic material in regolith samples. Since then, several removal mechanisms of organic material have been proposed. Two of these proposed methods are removal due to exposure to plasmas created in dust devils and exposure to UV irradiation. The experiments presented here were performed to identify similarities between the two potential removal mechanisms and to identify any compounds produced from these mechanisms that would have been difficult for the Viking instruments to detect. Five organic compounds, phenanthrene, octadecane, octadecanoic acid, decanophenone and benzoic acid, were exposed to a glow discharge plasma created in simulated martian atmospheres as might be present in dust devils, and to UV irradiation similar to that found at the surface of Mars. Glow discharge exposure was carried out in a chamber with 6.9 mbar pressure of a Mars like gas composed mostly of carbon dioxide. The plasma was characterized using emission spectroscopy and found to contain cations and excited neutral species including carbon dioxide, carbon monoxide, and nitrogen. UV irradiation experiments were performed in a Mars chamber which simulates the temperature, pressure, atmospheric composition, and UV fluence rates of equatorial Mars. The non-volatile residues left after each exposure were characterized by mass loss, infrared spectroscopy and high resolution mass spectrometry. Oxidized, higher molecular weight versions of the parent compounds containing carbonyl, hydroxyl and alkenyl functional groups were identified. The presence of these oxidized compounds suggests that searches for organic material in soils on Mars use instrumentation suitable for detection of compounds which contain the above functional groups. Discussions of possible reaction mechanisms are given. 相似文献
5.
Propagation of a quasi-neutral narrow ion beam across a magnetised cold plasma is investigated in slab geometry. This problem is of interest in connection with artificial beam injection experiments and with naturally appearing plasma injections into magnetic fields as astrophysical jets. Several different cases are discussed briefly where the beam is assumed either slow or fast. For fast beams it is shown that they propagate due to generation of a polarisation electric field even in the case of presence of a background plasma. Slow beams can depolarise by currents flowing into the beam along the field lines and providing the required electrons for charge neutralisation. Some implications of the model are discussed in the context of recent active beam injection experiments into space plasma. 相似文献
6.
J. C. Sherman 《Astrophysics and Space Science》1973,24(2):459-485
A review is given of the experimental investigations concerning the critical velocity of the interaction between a neutral
gas and a plasma in relative motion. In most of the experiments this critical velocity is equivalent to a voltage limitation
of a discharge through a partially ionized magnetized plasma. The critical velocity phenomenon can have been of importance
in a large number of experiments but it has been observed in rather few cases and studied in detail in less than half a dozen
plasma machines. The major investigations were made in rotating plasma devices like the Homopolar, plasma guns and a plasma-neutral
gas impact experiment. The emphasis of this paper is concentrated, though not limited, to collision-free plasmas. Thus the
(MPD-)arc experiments are not extensively treated. It is concluded that the existence, under certain conditions, of a critical
velocity, critical voltage or criticalE/B (depending on the particular observation) is proved by sufficient experimental evidence.
In a following article in this issue by J. Sherman the theoretical work in the same field is discussed. 相似文献
7.
C. D. Gregory J. Howe B. Loupias S. Myers M. M. Notley Y. Sakawa A. Oya R. Kodama M. Koenig E. Falize S. Bouquet C. Michaut N. C. Woolsey 《Astrophysics and Space Science》2009,322(1-4):37-41
We present the results of experiments in which jets are created through the collision of two laser-produced plasmas. These experiments use a simple ‘v-foil’ target design: two thin foils are placed at an angle of 140° to each other, and irradiated with a high-energy laser. The plasmas from the rear face of these foils collide and drive plasma jets moving with a velocity of ～300 km?s?1. By choosing the foil thickness and material to suit the laser conditions available, it has proven possible to create plasma jets for which the relevant scaling parameters show significant overlap with those of outflows associated with young stellar objects (YSOs). Preliminary results are also shown from experiments to study the effect of an ambient gas on jet propagation. Nominally identical experiments are conducted either in vacuum or in an ambient medium of 5 mbar of nitrogen gas. The gas is seen to increase the jet collimation, and to introduce shock structures at the head of the outflow. 相似文献
8.
V. I. Sotnikov R. Presura V. V. Ivanov T. E. Cowan J. N. Leboeuf B. V. Oliver 《Astrophysics and Space Science》2007,307(1-3):99-101
Laboratory experiments on the interaction of a plasma flow, produced by laser ablation of a solid target with the inhomogeneous
magnetic field from the Zebra pulsed power generator demonstrated the presence of strong wave activity in the region of the
flow deceleration. The deceleration of the plasma flow can be interpreted as the appearance of a gravity-like force. The drift
due to this force can lead to the excitation of flute modes. In this paper a linear dispersion equation for the excitation
of electromagnetic flute-type modes with plasma and magnetic field parameters, corresponding to the ongoing experiments is
examined. Results indicate that the wavelength of the excited flute modes strongly depends on the strength of the external
magnetic field. For magnetic field strengths ∼0.1 MG the excited wavelengths are larger than the width of the laser ablated
plasma plume and cannot be observed during the experiment. But for magnetic field strengths ∼1 MG the excited wavelengths
are much smaller and can then be detected. 相似文献
9.
B. Lehnert 《Astrophysics and Space Science》1988,144(1-2):31-42
The problem is considered of a cloud of neutral dust moving into a cloud of static plasma which is confined in a magnetic field. Earlier experiments with rotating plasma devices and plasma guns on critical velocity limitation suggest that such limitation could also arise in the case of plasma-neutral dust interaction in cosmos.Nevertheless further analysis is required to provide a clear picture of the relations between the cosmical and laboratory conditions for plasma-neutral gas and plasma-neutral dust interaction. In particular this applies to the question how to relate the experiments, which are largely in the plasma-physical MHD range, to the cosmical interaction which appears to be mainly governed by kinetic effects.Paper dedicated to Professor Hannes Alfvén on the occasion of his 80th birthday, 30 May 1988. 相似文献
10.
A. Frank E. G. Blackman A. Cunningham S. V. Lebedev D. Ampleford A. Ciardi S. N. Bland J. P. Chittenden M. G. Haines 《Astrophysics and Space Science》2005,298(1-2):107-114
We present new data from High-Energy Density (HED) laboratory experiments designed to explore the interaction of a heavy hypersonic
radiative jet with a cross wind. The jets are generated with the MAGPIE pulsed power machine where converging conical plasma
flows are produced from a cylindrically symmetric array of inclined wires. Radiative hypersonic jets emerge from the convergence
point. The cross wind is generated by ablation of a plastic foil via soft-X-rays from the plasma convergence region. Our experiments
show that the jets are deflected by the action of the cross wind with the angle of deflection dependent on the proximity of
the foil. Shocks within the jet beam are apparent in the data. Analysis of the data shows that the interaction of the jet
and cross wind is collisional and therefore in the hydrodynamic regime. We consider the astrophysical relevance of these experiments
applying published models of jet deflection developed for AGN and YSOs. We also present results of 3-D numerical simulations
of jet deflection using a new astrophysical Adaptive Mesh Refinement code. These simulations show highly structured shocks
occurring within the beam similar to what was observed in the experiments. 相似文献
11.
N. A. Tahir T. Stöhlker A. Shutov I. V. Lomonosov V. E. Fortov M. French N. Nettelmann R. Redmer A. R. Piriz C. Deutsch 《Astrophysics and Space Science》2011,336(1):61-65
Development of ultra-high power lasers has lead to the very interesting and important field of Laboratory Astrophysics. Recent
progress and expected near future developments in the technology of strongly bunched intense particle beams has opened up
the possibility of studying planetary interiors in the laboratory which hopefully will eventually converge in the new field
of Laboratory Planetary Physics. GSI Helmholzzentrum für Schwerionenforschung, Darmstadt is a well known laboratory worldwide
due to its unique particle accelerator facilities. Construction of the new huge accelerator complex, the Facility for Antiprotons
and Ion Research (FAIR), will substantially improve the existing capabilities of the GSI. A dedicated program named, HEDgeHOB,
that aims to study different problems in High Energy Density (HED) Physics at the FAIR facility, has been proposed. One of
these proposed experiments LAPLAS (LAboratory PLAnetary Science), aim to study materials at extreme conditions as relevant
for the interiors of giant planets. In this paper we present simulation results that show that various regions of the high-pressure
phase diagram of water can be probed within the LAPLAS experiments. For instance, the plasma and the superionic phase are
predicted to occur in the interior of water-rich planets such as Uranus and Neptune as well as in extrasolar planets such
as GJ 436b. 相似文献
12.
D. J. Mullan 《Solar physics》1977,54(1):183-206
Short-lived increases in the brightness of many red dwarfs have been observed for the last 30 yr, and a variety of more or less exotic models have been proposed to account for such flares. Information about flares in the Sun has progressed greatly in recent years as a result of spacecraft experiments, and properties of coronal flare plasma are becoming increasingly better known. In this paper, after briefly reviewing optical, radio and X-ray observations of stellar flares, we show how a simplified model which describes conductive plus radiative cooling of the coronal flare plasma in solar flares has been modified to apply to optical and X-ray stellar flare phenomena. This model reproduces many characteristic features of stellar flares, including the mean UBV colors of flare light, the direction of flare decay in the two-color diagram, precursors, Stillstands, secondary maxima, lack of sensitivity of flare color to flare amplitude, low flux of flare X-rays, distinction between so-called spike flares and slow flares, Balmer jumps of as much as 6–8, and emission line redshifts up to 3000 km s–1. In all probability, therefore, stellar flares involve physical processes which are no more exotic (and no less!) than those in solar flares. Advantages of observing stellar flares include the possibilities of (i) applying optical diagnostics to coronal flare plasma, whereas this is almost impossible in the Sun, and (ii) testing solar flare models in environments which are not generally accessible in the solar atmosphere. 相似文献
13.
Jesse C. James 《Solar physics》1970,12(1):143-162
The results of a series of radar studies of the sun at 38.2 MHz are presented. The echoes imply ever-present compressional waves in the corona, and these waves are likely associated with coronal heating. Some echoes are refracted by plasma clouds high in the corona. Other echoes are reflected by dense plasma irregularities moving outward very slowly at 0 to 20 km/sec. These are sometimes found as far out as three solar radii from the sun's center. Suggestions for future solar radar experiments and the need for them are outlined. 相似文献
14.
It is suggested that, in Petschek's model of magnetic field annihilation, plasma which flows through the boundary layer where its magnetic energy is released is rendered highly turbulent by current driven electrostatic instability. This leads to a physical insight into the mechanism of dissipation, and, by analogy with laboratory experiments on turbulent plasma, can explain the observed X-ray and microwave emissions.When the microstructure is calculated using electrical conductivity appropriate to highly turbulent plasma, a field configuration exists in which protons can be accelerated to very high energies. The results of some numerical calculations of this process are presented. 相似文献
15.
In the equatorial plasmasphere, plasma waves are frequently observed. To improve our understanding of the mechanism generating plasma waves from instabilities, a comparison of observations, linear growth-rate calculations, and simulation results is presented. To start the numerical experiments from realistic initial plasma conditions, we use the initial parameters inferred from observational data obtained around the plasma-wave generation region by the Akebono satellite. The linear growth rates of waves of different modes are calculated under resonance conditions, and compared with simulation results and observations. By employing numerical experiments by a particle code, we first show that upper hybrid-, Z-, and whistler-mode waves are excited through instabilities driven by a ring-type velocity distribution. The simulation results suggest a possibility that energetic electrons with energies of some tens of keV confined around the geomagnetic equator are responsible for the observed enhancements of Z- and whistler-mode waves. While the comparison between linear growth-rate calculations and observations shows the different tendency of wave amplitude of Z-mode and whistler-mode waves, the wave amplitude of these wave modes in the simulation results is consistent with the observation. 相似文献
16.
G. A. Doschek 《Solar physics》1983,86(1-2):49-58
17.
The efficiency with which critical ionization velocity (CIV) discharges can be generated in space experiments is affected by the altitude at which the experiments are conducted. At around 500 km higher plasma density enhances plasma lower hybrid instability, momentum coupling efficiency, and charge exchange which is needed for seed ionization. At higher altitudes where atomic hydrogen and helium become the dominant ambient neutral species, the conditions for CIV discharge may improve considerably because less energy is lost to atmospheric ionization, even though the ambient density is reduced. 相似文献
18.
The positron acoustic shock and solitary wave are explored in nonextensive electron-positron-ion plasma. The plasma system under-consideration, consists of a classical positron beam, q distributed electrons and positively charged bulky ions constitute a neutralizing background. The nonlinear Korteweg-de Vries and Burger equations are derived by employing the standard reductive perturbation method. The positron acoustic wave in linear limit is also discussed for dissipative as well as nondissipative cases of nonextensive plasmas. The plasma parameters such as, the concentration of neutralizing ions background, beam velocity, temperature and q parameter of the nonextensive electrons are noticed to significantly affect the positron acoustic shock and solitary waves. Our findings may be helpful in the understanding of laboratory beam plasma interaction experiments as well as the astrophysical nonextensive plasmas interacting with positron beam. 相似文献
19.
Similarity theory, which is necessary in order to apply the results of laboratory astrophysics experiments to relativistic
astrophysical plasmas, is presented. The analytical predictions of the similarity theory are compared with PIC numerical simulations
and the most recent experimental data on monoenergetic electron acceleration in diluted plasmas and high harmonic generation
at overdense plasma boundaries. We demonstrate that similarity theory is a reliable tool for explaining a surprisingly wide
variety of laboratory plasma phenomena the predictions of which can be scaled up to astrophysical dimensions. 相似文献
20.
Data observed during spacecraft encounters with magnetic clouds have been extensively analyzed in the literature. Moreover, several models have been proposed for the magnetic topology of these events, and fitted to the observations. Although these interplanetary events present well-defined plasma features, none of those models have included a simultaneous analysis of magnetic field and plasma data. Using as a starting point a non-force-free model that we have developed previously, we present a global study of MCs that include both the magnetic field topology and the plasma pressure. In this paper we obtain the governing equations for both magnitudes inside a MC. The expressions deduced are fitted simultaneously to the measurements of plasma pressure and magnetic field vector. We perform an analysis of magnetic field and plasma WIND observations within several MCs from 1995 to 1998. The analysis is confined to four of these events that have high-quality data. Only in one fitting procedure we obtain the orientation of the magnetic cloud relative to the ecliptic plane and the current density of the plasma inside the cloud. We find that the equations proposed reproduce the experimental data quite well. 相似文献