共查询到20条相似文献，搜索用时 234 毫秒
1.
Marian Karlický 《Astrophysics and Space Science》1997,257(2):249-257
A new mechanism for the generation of the electric ring current is presented. During the radial bombardment of a rotating
gas torus by a neutral beam, electrons and protons are dragged by rotating gas. Due to collisions electrons obtain the torus
velocity faster than protons, therefore in some layer there is a difference in electron and proton beam toroidal velocities;
the electric current is thus generated. This current is discussed as the seed magnetic field in early stages of evolving galaxies,
which is then amplified by the dynamo process to present values of the magnetic field.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
2.
A previous study of electromagnetic radiation from a finite train of electron pulses is extended to an infinite train of such pulses. The electrons are assumed to follow an idealized helical path through a space plasma in such a manner as to retain their respective position within the beam. This leads to radiation by coherent spontaneous emission. The waves of interest in this region are the whistler slow (compressional) and fast (torsional) Alfvén waves. Although a general theory is developed, analysis is then restricted to two approximations, the short and long electron beam. Formulas for the radiation per unit solid angle from the short beam are presented as a function of both propagation and ray angles, electron beam pulse width and separation and beam current, voltage, and pitch angle. Similar formulas for the total power radiated from the long beam are derived as a function of frequency, propagation angle, and ray angle. Predictions of the power radiated are presented for representative examples as determined by the long beam theory. 相似文献
3.
Yu. A. Rylov 《Astrophysics and Space Science》1978,53(2):377-402
It has been shown that vibrations can be generated in the electron cap of the neutron star (Rylov, 1976, 1977; Jackson, 1976) under certain conditions. The mechanism of generation is like that in a klystron. The electron gas of the cap plays the role of the klystron resonant circuit. The electron beam penetrating the electron cap and returning to the star's surface plays the role of the klystron electron beam. The bunching electron stream along the magnetic axis acts like a strongly directed antenna. The conditions in which it is possible to generate these vibrations were also investigated. The energy of the accelerated primary electrons, the frequency of radiated radiowaves and the degree of the radiation directivity are evaluated. 相似文献
4.
The critical velocity triggering anomalous ionization of the neutral gas by plasma flow is calculated for the model based on the lower hybride instability. It depends strongly on the plasma and gas parameters, denning the instability development of the ionized atoms beam in the counter-streaming plasma.In particular, the possible role of the critical ionization mechanism for Halley's comet is examined. The fulfilment of both Townsend's condition for the selfustained beam plasma discharge and Alfven's condition for the critical velocity mechanism indicates that this mechanism may operate only within 104 km from the cometary nucleus and give an ion production rate close to that observed for Kohoutek's comet. 相似文献
5.
Yasunori Nejoh 《Astrophysics and Space Science》1996,235(2):245-253
The stationary ion-acoustic double layer is investigated in a plasma with an electron beam. The condition of the existence sensitively depends on the parameters such as the electron beam temperature, the ion temperature, the beam density and the effect of the trapped electrons. The properties of the double layer are also depicted. It turns out that the electron beam velocity is relatively small. This investigation predicts new findings of the ion-acoustic double layers in a plasma with an electron beam. 相似文献
6.
7.
The POLAR 5 sounding rocket, launched from Andøya, Norway, on February 1, 1976, was of the “mother-daughter” configuration.A rocket-borne electron accelerator, mounted on the “daughter,” produced a pulsed electron beam with a maximum current of 130 mA and electron energies up to 10 kev.Using a photometer the luminescence at 391.4nm produced by electrons colliding with ambient nitrogen molecules was studied. The observed light at 391.4 nm consisted of low background, with occasional flashes due to the natural auroral excitations, and intense sparkles when the electron beam was emitted.Below 130 km the light observed during beam injection can be explained by excitations of ambient N2 due to high energy beam electrons.In the altitude range from 150 km to apogee at 220 km, the observed light level during beam emission is fairly constant and much larger than that produced by the high energy beam electrons. A possible source of this light is the excitation of ambient N2 by an enhanced population of low energy electrons, created by the presence of a beam plasma discharge in the vicinity of the “daughter” payload. 相似文献
8.
《Chinese Astronomy and Astrophysics》1982,6(3):192-198
We investigate the possibility of an additional acceleration of the high speed solar wind by whistler waves propagating outward from a coronal hole. We consider a stationary, spherically symmetric model and assume a radial wind flow as well as a radial magnetic field. The energy equation consists of (a) energy transfer of the electron beam which excites the whistler waves, and (b) energy transfer of the whistler waves described by conservation of wave action density. The momentum conservation equation includes the momentum transfer of two gases (a thermal gas and an electron beam). The variation of the temperature is described by a polytropic law. The variation of solar wind velocity with the radial distance is calculated for different values of energy density of the whistler waves. It is shown that the acceleration of high speed solar wind in the coronal hole due to the whistler waves is very important. We have calculated that the solar wind velocity at the earth's orbit is about equal to 670 km/sec (for wave energy density about 10?4 erg cm?3 at 1.1R⊙). It is in approximate agreement with the observed values. 相似文献
9.
As one of the most violent activities in the solar atmosphere,white-light flares(WLFs)are generally known for their enhanced white-light(or continuum)emission,which primarily originates in the solar lower atmosphere.However,we know little about how white-light emission is produced.In this study,we aim to investigate the response of the continua at 3600?and 4250?and also the Hαand Lyαlines during WLFs modeled using radiative hydrodynamic simulations.We take non-thermal electron beams as the energy source for the WLFs in two different initial atmospheres and vary their parameters.Our results show that the model with non-thermal electron beam heating clearly shows enhancements in the continua at 3600?and 4250?as well as in the Hαand Lyαlines.A larger electron beam flux,a smaller spectral index,or an initial penumbral atmosphere leads to a stronger emission increase at 3600?,4250?and in the Hαline.The Lyαline,however,is more obviously enhanced in a quiet-Sun initial atmosphere with a larger electron beam spectral index.It is also notable that the continua at 3600?and 4250?and the Hαline exhibit a dimming at the start of heating and reach their peak emissions after the peak time of the heating function,while the Lyαline does not show such behaviors.These results can serve as a reference for the analysis of future WLF observations. 相似文献
10.
Huang Guang-Li Qin Zhi-Hai Yan Guo Fu Qi-Jun Liu Yu-Ying 《Astrophysics and Space Science》1998,259(3):317-326
A typical event of solar microwave type III burst with both positive and negative frequency drifts was observed by the 1–2
GHz spectrograph at Beijing Observatory on January 5, 1994. The separatrix frequency (1.3 GHz) may correspond to an acceleration
region. The energy of the electron beam responsible for the burst is calculated from the drift rate and the height of the
source above the photosphere. Moreover, if the solar microwave type III burst is explained by the beam-plasma instability
as suggested by Huang (1998), the energy density as well as the particle density of the electron beam may be estimated from
the burst flux, the growth rates and the modularity (Huang et al., 1996). So that, a very good power- law distribution is
simulated for the energetic spectrum of the electron beam in this event with a spectrum index 4.5. The electron beam may be
accelerated by an electric field with a length of 107 m and a strength of <10-4 V m- 1. These results are necessary for understanding the acceleration process in solar flares.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
11.
M. Favre J. Moreno H. Chuaqui E. Wyndham M. Zambra P. Choi C. Dumitrescu-Zoita 《Astrophysics and Space Science》1997,256(1-2):337-342
Discharge formation in the A–K space of transient hollow cathode discharge (THCD) is causally linked with the emission of high energy electron beams originating in the hollow cathode region (HCR). Ionization in the A–K gap proceeds through the formation of a moving virtual anode, whose time evolution is strongly correlated with different periods in the electron beam activity. Here, we report on time and space resolved observations of different ionization events inside the HCR, which are time correlated with ionization processes inside the A–K gap. The experiments have been performed in Hydrogen, at pressures between 50 and 400 mTorr. A statistical study of the characteristic times associated with the different ionization events, based on von Laue plots, shows that the time distribution of events is well described by a single Gaussian distribution. 相似文献
12.
Gui-Yun Liang Hui-Gang Wei Da-Wei Yuan Fei-Lu Wang Ji-Min Peng Jia-Yong Zhong Xiao-Long Zhu Mike Schmidt Günter Zschornack Xin-Wen Ma Gang Zhao 《天文和天体物理学研究(英文版)》2018,(1)
Spectra are fundamental observation data used for astronomical research,but understanding them strongly depends on theoretical models with many fundamental parameters from theoretical calculations.Different models give different insights for understanding a specific object.Hence,laboratory benchmarks for these theoretical models become necessary.An electron beam ion trap is an ideal facility for spectroscopic benchmarks due to its similar conditions of electron density and temperature compared to astrophysical plasmas in stellar coronae,supernova remnants and so on.In this paper,we will describe the performance of a small electron beam ion trap/source facility installed at National Astronomical Observatories,Chinese Academy of Sciences.We present some preliminary experimental results on X-ray emission,ion production,the ionization process of trapped ions as well as the effects of charge exchange on the ionization. 相似文献
13.
Characteristics of the astrophysical important Stark broadened 388.86 nm, 471.32 nm and 501.56 nm He I spectral line profiles have been measured at electron densities between 4.4·1022 and 8.2·1022 m−3 and electron temperatures between 18,000 and 33,000 K in plasmas created in five various discharge conditions using a linear, low-pressure, pulsed arc as an optically thin and reproductive plasma source operated in a helium–nitrogen–oxygen gas mixture. On the basis of the observed asymmetry of the line profiles, we have obtained their ion broadening parameters (A) caused by influence of the ion microfield and also the influence of the ion dynamic effect (D) to the line shape. Our A and D parameters represent the first data obtained experimentally by the use of the line profile deconvolution procedure. We have found stronger influence of the ion contribution to these He I line profiles than the semiclassical theoretical approximation provides. This can be important for some astrophysical plasma modelling or for diagnostics. 相似文献
14.
The dynamics of an electron beam is considered when the initial electron distribution is localized in a space region. Analysis is conducted for the parameters of the beam and plasma that give radio emission. We demonstrate both numerically and analytically that beam electrons propagate as a beam-plasma structure at large distances. The speed of the beam-plasma structure is equal to half of the maximum velocity of the electrons involved in this structure. The structure conserves the shape of the initial spatial distribution of electrons. A plateau with a constant maximum velocity is formed at the electron distribution function in each spatial point. 相似文献
15.
A method is described for the analytical evaluation of the force acting on a relativistic electron beam spreading in dense gas plasma by the ohmic plasma channel. This is useful for the solution of the general definitions for the force of the beam plasma interactions in the case of an arbitrary displacement of the symmetry axis of the plasma channel relative to the corresponding axis of the beam. The accuracy of these procedures is tested and their efficiency illustrated with practical applications, including the computation of the tracking force exerting on a relativistic electron beam by the ohmic plasma channel. 相似文献
16.
Electron-acoustic waves are studied with orbital angular momentum (OAM) in an unmagnetized collisionless uniform plasma, whose constituents are the Boltzmann hot electrons, inertial cold electrons and stationary ions. For this purpose, we employ the fluid equations to obtain a paraxial equation in terms of cold electron density perturbations, which admits both the Gaussian and Laguerre–Gaussian (LG) beam solutions. Furthermore, an approximate solution for the electrostatic potential problem is found, which also allows us to express the components of the electric field in terms of LG potential perturbations. Calculating the energy flux of the electron-acoustic waves, an OAM density for these waves is obtained. Numerically, it is found that the parameters, such as, azimuthal angle, radial and angular mode numbers, and the beam waist strongly modify the LG potential profiles associated with electron-acoustic waves. The present results should be helpful to study the trapping and transportation of plasma particles and energy as well as to understand the electron-acoustic mode excitations produced by the Raman backscattering of laser beams in a uniform plasma. 相似文献
17.
《New Astronomy》2004,9(8):629-633
Stark widths (W) and shifts (d) of the astrophysically very important singly ionized magnesium (Mg II) resonance h and k (279.5528 and 280.2705 nm) spectral lines in the 3s–3p transition have been measured at a 26,000 K electron temperature and 1.1 × 1023 m−3 electron density in helium–oxygen plasma created in an optically thin linear, low-pressure, pulsed arc discharge. The magnesium atoms, as impurities in the driving gas, have been introduced by erosion from the pure magnesium bands fixed on the discharge electrodes providing conditions free of the self-absorption in the resonance h and k lines. Besides, the W and d values of the 279.0777 nm and 279.7998 nm Mg II lines in the 3p–3d transition have also been measured. Our W and d have been compared to the existing experimental and theoretical data. Good agreement was found with the results calculated by the semiclassical perturbation formalism, especially in the case of the Stark widths. 相似文献
18.
Fabrice Doveil Alessandro Macor Anass Aïssi 《Celestial Mechanics and Dynamical Astronomy》2008,102(1-3):255-272
The motion of charged particle in longitudinal waves is a paradigm for the transition to large scale chaos in Hamiltonian systems. Recently a test cold electron beam has been used to observe its non-self-consistent interaction with externally excited wave(s) in a specially designed Traveling Wave Tube (TWT). The velocity distribution function of the electron beam is recorded with a trochoidal energy analyzer at the output of the TWT. An arbitrary waveform generator is used to launch a prescribed spectrum of waves along the slow wave structure (a 4 m long helix) of the TWT. The resonant velocity domain associated to a single wave is observed, as well as the transition to large scale chaos when the resonant domains of two waves and their secondary resonances overlap. This transition exhibits a “devil’s staircase” behavior when increasing the excitation amplitude in agreement with numerical simulation. A new strategy for control of chaos by building barriers of transport which prevent electrons to escape from a given velocity region as well as its robustness are also successfully tested. Thus generic features of Hamiltonian chaos have been experimentally observed. 相似文献
19.
This is a quantitative investigation of the electron beam effect on the hydrogen line profiles and continuum intensity distribution during the impulsive phase of flares. The flaring atmosphere is suggested to be a hydrogenic one and its physical condition corresponds to the gas dynamics problem solution. The radiative transfer, steady-state and particle conservation equations are solved for the three-level hydrogen model atoms with continua. Return-current losses were neglected. Hydrogen line profiles are found to be slightly sensitive to nonthermal impacts with beam electrons in the cores and more sensitive in the wings. With the initial energy flux,F
0, rising and energy spectral index, , decreasing, the wing intensities begin to increase, and the H lines are shown to have rather extended wings as is often observed. The hydrogen continua are shown to be strongly affected by nonthermal impacts. The bigger the value ofF
0 and the smaller the value of , the greater absolute intensities of the hydrogen continua heads. This effect is more noticeable for the Balmer and Paschen continua. The head intensity slopes of them can be used for determination of these electron beam parameters on depths of the hydrogen emission origin and their following comparison with the same parameters for the coronal heights from the X-ray observations. 相似文献
20.
K. R. Anantharamaiah 《Journal of Astrophysics and Astronomy》1985,6(4):203-226
The recent survey of H 272α recombination line (324.99 MHz) in the direction of 34 Hn regions, 12 SNRs and 6 regions of continuum
minimum (‘blank’ regions) in the galactic plane is used to derive the properties of diffuse ionized gas in the inner Galaxy.
The intensity of radio recombination lines at high frequencies is dominated by spontaneous emission in high-density gas and
that at low frequencies (325 MHz) by stimulated emission in low-density gas. We have used this property to obtain the electron
density in the gas in the direction of blank regions and SNRs, by combining the H 272 α measurements (preceeding paper) with
the published data at higher frequencies. Further, we have imposed constraints on the electron temperature and pathlength
through this gas using the observed high-frequency continuum emission, average interstellar electron density and geometry
of the line-emitting regions. The derived properties of the gas are (i) electron density 0.5–6 cm-3, (ii) electron temperature 3000–8000 K and (iii) emission measures 500–3000 pc cm-6 The corresponding pathlengths are 50–200 pc.
As the derived sizes of the low-density regions are small compared to the pathlength through the Galaxy, the low-frequency
recombination lines cannot be considered as coming from a widely distributed component of the interstellar medium.
The Hn regions studied in the above survey cannot themselves produce the H 272α lines detected towards them because of pressure
broadening, optical depth, and beam dilution. However, the agreement in velocity of these lines with those seen at higher
frequencies suggests that the low-frequency recombination lines arise in low-density envelopes of the Hn regions. Assuming
that the temperature of the envelopes are similar to those of the cores and invoking geometrical considerations we find that
these envelopes should have electron densities in the range 1–10 cm-3 and linear sizes of 30–300 pc in order to produce the observed H 272α lines. 相似文献