共查询到20条相似文献,搜索用时 15 毫秒
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The steady-state electric-current distribution and the magnetic pressure in a uniform conducting medium, flowing in a cylindrical configuration between two circular electrodes, was determined by solving the magnetic field transport equation with a superimposed axial magnetic field. This medium models the interelectrode plasma of the diffuse mode metal vapor vacuum arc. The results show the following. a) The electric current and the flux of the poloidal magnetic field are constricted at the anode side of the flowing plasma. Most of the constriction takes place within a boundary layer, with a characteristic length of 1/Rme, where Rme is the magnetic-Reynolds number for axial electron flow. b) The electric-current constriction inversely depends on K?, where K? is the azimuthal surface current density which produces the axial magnetic field. c) The magnetic-pressure profile shows a radial pinch force in most of the interelectrode region, but in the anode boundary layer it is axially directed, thus retarding the plasma flow. d) The peak of the magnetic pressure is at the anode, and its amplitude directly depends on K?. As K? increases, the peak location moves toward the anode center. 相似文献
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As vacuum arcs subjected to a magnetic field parallel to their positive column (an axial magnetic field) spread uniformly over all the electrodes and burn in the interelectrode region, arc voltages of these arcs are low and quiescent. When the magnetic field strength decreases, however, the arc voltage develops a large noise component and electrode melting occurs. Experiments were conducted to investigate the condition of these transition phenomena. As a result of these experiments, it was found that these two phenomena do not always occur simultaneously and that a new explanation for the mechanism of anode spot formation should be considered. 相似文献
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When an axial magnetic field is applied to a vacuum arc, the arc tends to be stabilized in its diffuse mode. A minimum arc voltage is found for a certain magnetic field. In this condition, interrupting current is significantly increased, and it is nearly proportional to the diameter of electrodes. About ten years ago, a practical axial magnetic field electrode was developed for vacuum circuit breakers. Since then, through various improvements in its structure, this electrode has been refined for practical application in vacuum circuit breaker interrupters. The application has successfully covered not only medium-voltage circuit breakers, but also high-voltage (84 kV), dc high-voltage, and high-current circuit breakers. In this paper, ten years experience in this area is described. 相似文献
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首先叙述了由单个轴向磁化环所产生的磁场,并就两个永磁环所产生的纵向磁场进行了分析.对于两个沿同一方向磁化的永磁体环,沿磁环中心线将会产生一个强度较为均匀的轴向磁场.如果两者的磁化方向相反,则在两磁铁间的区域将产生一个纵向的梯度磁场,其磁场强度介于-B0到+B0之间.设计制造了一个高梯度的轴向磁场,其磁场梯度为47.2Tm,测量结果与计算结果非常一致.文中还讨论了产生变梯度磁场的方法.由于永磁环所产生的磁场和螺线管的磁场较为相似,磁铁外部空间将有较大的漏场,最后还讨论了屏蔽漏场的问题. 相似文献
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Wenxin Liu Ziqiang Yang Zheng Liang 《International Journal of Infrared and Millimeter Waves》2006,27(8):1073-1085
A model of two-stream Free-Electron Lasers (FEL) with an axial guiding magnetic field (AGMF) is proposed and investigated
in this paper. The dispersion relation is derived employing linear fluid theory. The characteristics of dispersion relation
are analyzed in detail by numerical solutions, which show that the growth rate can be considerably enhanced and the operation
frequency is significantly broader with the suitable of AGMF, separation velocity and beams’ relative density factor, and
the occurrences of two-stream instability in FEL are stronger due to the presence of AGMF. 相似文献
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Russian Physics Journal - The effect of a relatively short external axial magnetic field on the characteristics of a vacuum arc discharge in a vacuum circuit breaker is studied. A pulsed magnetic... 相似文献
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We calculate the energy states and Aharonov--Bohm oscillations of an electron in elliptical quantum rings in the presence of a uniform magnetic field by using an exact numerical diagonalization. The calculated results show that the elliptical quantum rings are flatter, larger amplitudes and periods of the Aharonov--Bohm oscillations are observed. In addition, in the limits of a circular quantum ring, the results of our approach are in good agreement with those of earlier theories. 相似文献
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Experimental measurements in a vacuum interrupter have shown that the application of a transverse magnetic field results in substantial increases in arc voltage. Photographic studies of the arc column indicate that strong magnetic fields reduce the effective anode area and may lead to severe arc constriction. 相似文献
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Electron-Cyclotron Laser Using Free-Electron Two-Quantum Stark Radiation in a Strong Uniform Axial Magnetic Field and an Alternating Axial Electric Field in a Voltage-Supplied Pill-Box Cavity 下载免费PDF全文
《中国物理快报》2016,(3)
We consider the radiation from the beam electrons traveling in a strong uniform axial magnetic field and an axiai alternating electric field of wavelength λ_w generated by a voltage-supplied pill-box cavity.The beam electrons emit genuine laser radiation that propagates only in the axial direction through free-electron twoquantum Stark radiation.We find that laser radiation takes place only at the expense of the axial kinetic energy when λ_wc/(ω_c/γ),where ω_c/γ is the reiativistic electron-cyclotron frequency.We formulate the laser power based on quantum-wiggler electrodynamics,and envision a laser of length 10 m with estimated power 0.1 GW/(kA) in the 10~(-4) cm wavelength range. 相似文献
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Schneider A. V. Popov S. A. Dubrovskaya E. L. Batrakov A. V. 《Russian Physics Journal》2019,62(5):900-905
Russian Physics Journal - The influence of an external synchronous axial magnetic field on the characteristics of a vacuum-arc discharge is investigated within the range of discharge currents from... 相似文献
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In order to explore the inducing factors and mechanism of the non-synchronous vibration, the flow field structure and its formation mechanism in the non-synchronous vibration state of a high speed turbocompressor are discussed in this paper, based on the fluid–structure interaction method. The predicted frequencies fBV (4.4EO), fAR (9.6EO) in the field have a good correspondence with the experimental data, which verify the reliability and accuracy of the numerical method. The results indicate that, under a deviation in the adjustment of inlet guide vane (IGV), the disturbances of pressure in the tip diffuse upstream and downstream, and maintain the corresponding relationship with the non-synchronous vibration frequency of the blade. An instability flow that developed at the tip region of 90% span emerged due to interactions among the incoming main flow, the axial separation backflow, and the tip leakage vortices. The separation vortices in the blade passage mixed up with the tip leakage flow reverse at the trailing edge of blade tip, presenting a spiral vortex structure which flows upstream to the leading edge of the adjacent blade. The disturbances of the spiral vortexes emerge to rotate at 54.5% of the rotor speed in the same rotating direction as a modal oscillation. The blade vibration in the turbocompressor is found to be related to the unsteadiness of the tip flow. The large pressure oscillation caused by the movement of the spiral vortex is regarded as the one of the main drivers for the non-synchronous vibration for the present turbocompressor, besides the deviation in the adjustment of IGV. 相似文献
16.
M. Sato 《等离子体物理论文集》1981,21(2):77-86
Influences of an axial magnetic field on the ionization wave and the positive column in rare gas discharges are studied experimentally. The upper critical current Ic for the appearance of ionization waves in the magnetic field B is newly found. As B is gradually increased, the value of Ie slightly increases from the Pupp's value and after passing a prominent maximum, finally become very small. In addition an anomaly takes place in the axial electric field E of the positive column stable for helical instabilities. With increasing the magnetic field the value of E goes through a weak maximum before decreasing. It is concluded that this anomaly, apparently incompatible with classical diffusion theory, is closely related to the appearance of ionization waves in the positive column. 相似文献
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Hiroshi Tsukuda Masaru Masuzaki Norio Toyosugi Cha Yeol Lee Ritoku Ando Keiichi Kamada Tsuguhiro Watanabe 《International Journal of Infrared and Millimeter Waves》2001,22(8):1147-1162
A linear analysis is described on stabilities driven by an intense relativistic electron beam in an infinitely long, plasma-filled, and dielectric-lined circular waveguide immersed in a finite strength axial magnetic field. A dispersion equation is derived from the cold fluid theory and solved numerically. Beam-plasma instabilities due to interaction between beam modes and the Trivelpiece-Gould modes appear as well as the Cherenkov and the cyclotron Cherenkov instabilities. Parametric researches are carried out varying magnetic field strength, plasma density, and dielectric constant. Effects of a finite magnetic field and plasma filling are discussed in connection with the possibilities of using this system as a microwave radiation source. 相似文献
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Magnetic resonance imaging is well known as a highly effective technique of medical visualization. One of its relatively new approaches is diffusion imaging. As a rule, the majority of magnetic resonance investigations in biology and medicine tends to be carried out in high magnetic fields (1.5 T and higher), but there are some advantages of the same experiments in low magnetic fields. It can be strongly useful, for example, for designing and testing new pulse sequences, training operators of magnetic resonance imagers, making new phantoms (model objects). In this study, diffusion-weighted imaging experiments in a low magnetic field 7 mT are performed in the first time. Nevertheless, this field is about two orders of magnitude bigger than an extremely low Earth field, and so concomitant gradients and polarization problems do not arise. In particular, diffusion weighted images of combined model samples (phantoms) are presented. 相似文献
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A fluid Maxwell theory has been derived to study a system of multibeams propagating parallel to an applied axial magnetic field in an evacuated conducting drift tube. The stability analysis is performed for a rigid-rotor and cold-laminar flow equilibria. It is assumed that the particle beams are tenuous and the guiding field is very strong. As a result, the perturbation theory is derived under the condition that the plasma frequency is much smaller than the cyclotron frequency for each beam particle. A dispersion relation is obtained for a special case of sharp-boundary density profiles. The stability properties of infinitely long beams are illustrated in detail for different geometries and various beam parameters. The results agree with those obtained by Uhm [8] in a special case where a solid electron beam propagates through an annular electron beam. The finite geometry effect of the accelerator is discussed briefly. It might have a substantial influence on the behavior of a real device. 相似文献