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1.
An analytical solution of the problem on the initial stage of the formation of a virtual cathode in an electron beam passing through a dielectric medium is presented. 相似文献
2.
The Peccei-Quinn (PQ) solution of the strong CP problem requires the existence of axions, which are viable candidates for dark matter. If the Nambu-Goldstone potential of the PQ model is replaced by a potential V(|Phi|) admitting a tracker solution, the scalar field |Phi| can account for dark energy, while the phase of Phi yields axion dark matter. If V is a supergravity (SUGRA) potential, the model essentially depends on a single parameter, the energy scale Lambda. Once we set Lambda approximately equal to 10(10) GeV at the quark-hadron transition, |Phi| naturally passes through values suitable to solve the strong CP problem, later growing to values providing fair amounts of dark matter and dark energy. 相似文献
3.
Comparative investigation of two forms of attachment of a dc (20 < I < 200 A) atmospheric-pressure arc in argon to a thermionic cathode made of pure tungsten is carried out. The current-voltage characteristics of the arc, axial distribution of the cathode rod surface temperature (except for the site of arc attachment), and plasma temperature axial distribution in the cathode region are measured, and the current density on the cathode surface is estimated. The measurements of current-voltage curves shows that the voltages of the arc with different forms of cathode attachment differ distinctly (but not too much) one from another, the curves for two modes iontersect. This confirms the results of theoretical analysis carried out earlier by M.S. Benilov who has showed that an existence of different forms of attachment is associated with the presence of branching points in a solution to the cathode heat balance problem. The point of intersection should be viewed as one such point. Optical measurements disclose that the temperature and its distribution over the cathode rod surface differ greatly for the two forms of attachment considered. The plasma temperature in the cathode region of the contracted attachment far exceeds that in the diffuse attachment, exceeding 3 eV in the immediate vicinity of the cathode surface. The maximal temperature of the plasma in the contracted attachment does not depend on the current. Analysis of erosion prints shows that the current density on the cathode does not depend on the current for both forms of cathodic attachment. For the contracted attachment, the current density is roughly four times higher (~104 A/cm2) than for the diffuse form. The experimental data are in good agreement with present-day calculations of the cathode plasma parameters and temperature conditions. 相似文献
4.
Relation between space-charge-limiting current and electric field enhancement factor at curved surface cathode 下载免费PDF全文
A two-dimensional solution of space-charge-limiting current for a high current vacuum diode with a spherical cathode is presented. The relation between space-charge-limiting current and electric field enhancement factor at the cathode surface for the diode with a curved surface cathode is also discussed. It is shown that compared with the current given by the conventional Child—Langmuir law, which describes the one-dimensional space-charege-limiting current, the two-dimensional space-charge-limiting current in such a diode is enhanced due to the electric-field enhancement along the cathode surface. Among practical parameter ranges, enhancement factor ηb approximately satisfies ηb ≈ Aβn, where β is the electric field enhancement factor at the cathode surface, and n is a constant between 1 and 2, which is confirmed to be universal for the diodes with curved surface cathodes. 相似文献
5.
An electron gun using lanthanum hexaboride (LaB6) as a cathode material is being studied for use as a robust thermionic emitter at high cathode current densities. It has a standard planar cathode, Pierce-type electron gun design with a space-charge-limited perveance of 3.2 × 10-6 A/V3/2. Thus far it has been operated up to 36 kV in the space-charge-limited regime. The cathode is heated by electron bombardment and radiation from an auxiliary tungsten filament. The total heating requirement is found to be 202 W/cm2 of cathode area at a cathode temperature of 1626°C. These observations are found to be in reasonable agreement with a thermal steady-state power balance model. Beam current distribution measurements are made with a movable collector and Faraday cup, and are found to be in agreement with an electron-gun computer code. The cathode temperature distribution is also measured. 相似文献
6.
An abrupt change in the spectral width of optogalvanic (OG) signals of Kr atomic lines has been observed at a distance from the cathode wall where the signal itself changes its sign, by using a hollow cathode lamp whose cathode has its both ends open. The width is broader near the cathode wall with its magnitude varying by discharge current while the narrower width which is obtained on passing the laser beam in the central region of cathode cylinder is independent of the current. It is suggested that a well-defined region, where the particles of larger cross section of collisions with Kr atom are confined, is present in front of the cathode wall. 相似文献
7.
The steady-state electric current distribution in a multicathode-spot vacuum arc was determined by a solution of the magnetic transport equation subject to various boundary conditions. The inter-electrode region of the arc is modeled as a uniform plasma flowing from the cathode to the anode. Dimensional analysis shows that three parameters determine the magnetic field, and hence the current density which is derived from it: AR-the ratio of the electrode separation to the electrode radius, Rmm-magnetic Reynolds number of the axial material flow, and Rme-magnetic Reynolds number of the axial electron flow. While the anode side of the conducting medium is described as an equipotential surface, the following three cases of boundary conditions for the cathode side are examined: 1) a known current density distribution is assumed over the entire cathode side of the plasma surface; 2) the cathode side is an equipotential surface; and 3) the current is allowed to cross the cathode surface only through a finite number of ring shaped regions. Numerical solutions of the nonlinear magnetic transport equation show a constriction of the current at the anode side for all boundary conditions mentioned. On the other hand, the current moves to the perimeter of the cathode for boundary condition 2). When AR, Rmm, and Rme equal 0.72,-0.16, and 1.73, respectively, and a uniform current density flows at the cathode side, the on-axis current density at the anode is six times larger than its value at the cathode. 相似文献
8.
在现行光学教材中有一道关于迈克耳孙干涉仪的应用例题,由于忽略了一个极微小的细节,使得计算结果出现了偏差.本文对此问题进行了详细的分析. 相似文献
9.
The current of a steady-state electron beam emitted from the magnetically insulated, finite-emissivity edge cathode of a two-electrode coaxial gun is calculated. The dependence of the emission current on the applied voltage is analyzed by solving a self-consistent problem. The field structure near the cathode edge is investigated, and its dependence on the current of the generated electron beam is determined. 相似文献
10.
A physical model of a self-sustaining reflective discharge is formulated based on the continuity equation for the electron
flux and the equation of energy balance on the hot cathode. The model allows one to calculate the current-voltage characteristic
of a high current reflective discharge with a hot cathode in a wide range of magnetic fields, discharge cell dimensions, and
cathode material work functions. An advantage of the model is that it is capable of describing the ordinary operating mode
of a reflective discharge with cold cathodes as a limiting case. The model predicts the existence of two discharge operating
modes with thermionic electron emission on the cathode: a low-voltage mode with a high current density and a high-voltage
mode with a significantly lower current density. It is shown that the low-voltage operating mode can occur in a wide range
of the discharge currents, while the discharge voltage can be substantially reduced by using a cathode material with a low
work function. 相似文献
11.
A. I. Arbuzov 《Russian Physics Journal》1988,31(10):810-814
A numerical study is performed of a one-dimensional model of a high current plasma-filled diode, connected in a circuit with a voltage generator. Flow of the plasma from an external source into the diode anode-cathode gap through the plane of the cathode grid proves to have a definite effect on the diode current-voltage characteristic. An estimate is made of the limiting current above which formation of a cathode double layer occurs. Generation of explosive emission at a high value of current or the time derivative of current causes rapid expansion of the cathode layer due to a lack of the majority, electron current component and the presence of a phase intensified by plasma erosion. Dependence of the current-voltage characteristic on density of cathode explosive emission centers is noted.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 48–53, October, 1988. 相似文献
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13.
Abulencia A Adelman J Affolder T Akimoto T Albrow MG Ambrose D Amerio S Amidei D Anastassov A Anikeev K Annovi A Antos J Aoki M Apollinari G Arguin JF Arisawa T Artikov A Ashmanskas W Attal A Azfar F Azzi-Bacchetta P Azzurri P Bacchetta N Badgett W Barbaro-Galtieri A Barnes VE Barnett BA Baroiant S Bartsch V Bauer G Bedeschi F Behari S Belforte S Bellettini G Bellinger J Belloni A Benjamin D Beretvas A Beringer J Berry T Bhatti A Binkley M Bisello D Blair RE Blocker C Blumenfeld B Bocci A 《Physical review letters》2007,98(12):122001
We report a measurement of the Lambda b0 lifetime in the exclusive decay Lambda b0-->J/psi Lambda 0 in pp collisions at square root s=1.96 TeV using an integrated luminosity of 1.0 fb-1 of data collected by the CDF II detector at the Fermilab Tevatron. Using fully reconstructed decays, we measure tau(Lambda b0)=1.593(-0.078)(+0.083)(stat)+/-0.033(syst) ps. This is the single most precise measurement of tau(Lambda b0) and is 3.2sigma higher than the current world average. 相似文献
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Iodice M Cusanno F Acha A Ambrozewicz P Aniol KA Baturin P Bertin PY Benaoum H Blomqvist KI Boeglin WU Breuer H Brindza P Bydzovský P Camsonne A Chang CC Chen JP Choi S Chudakov EA Cisbani E Colilli S Coman L Craver BJ De Cataldo G de Jager CW De Leo R Deur AP Ferdi C Feuerbach RJ Folts E Fratoni R Frullani S Garibaldi F Gayou O Giulani F Gomez J Gricia M Hansen JO Hayes D Higinbotham DW Holmstrom TK Hyde CE Ibrahim HF Jiang X Kaufman LJ Kino K Kross B Lagamba L LeRose JJ Lindgren RA 《Physical review letters》2007,99(5):052501
An experiment measuring electroproduction of hypernuclei has been performed in hall A at Jefferson Lab on a 12C target. In order to increase counting rates and provide unambiguous kaon identification two superconducting septum magnets and a ring imaging Cherenkov detector were added to the hall A standard equipment. An unprecedented energy resolution of less than 700 keV FWHM has been achieved. Thus, the observed (Lambda)(12)B spectrum shows for the first time identifiable strength in the core-excited region between the ground-state s-wave Lambda peak and the 11 MeV p-wave Lambda peak. 相似文献
16.
We investigated the decolorization of acid red B in aqueous solution by atmospheric discharge. It was found that decolorization was significantly greater when the aqueous solution served as the cathode than when it served as the anode. Our investigation suggests that hydroxyl radicals could be a major factor for decolorization in the solution phase. An analysis of the energy transportation by charge carriers in the discharge processes revealed that the mean energy transported from positive ions to the aqueous cathode was considerably higher than that transported from electrons/negative ions to the aqueous anode, and this could probably have indirectly affected the decolorization. 相似文献
17.
利用Na2SiO3-KOH溶液体系,以工业纯铝为基体材料对约束阴极微弧氧化的放电特性进行了研究.考察了恒压模式下电极距离对氧化电流、电位分布及起弧电压的影响,并对电极距离与微弧氧化电能利用率间的关系进行了分析. 结果表明:对于阴阳极等约束条件下,随阴阳极距离加大,工作电流逐渐减小. 而对于仅约束阴极情况,工作电流随着阴阳极间距增加而增大. 这是由于增加阴阳极间距时,虽然约束阴极正下方试样表面的电场强度降低,工作电流减小,但远离约束电极处,阳极表面电场强度却增加,工作电流增大. 起弧电压随电极间距离的增大而升高,但阳极表面电场强度几乎保持不变. 微弧氧化陶瓷层厚度由处理中心沿半径向外逐渐变薄,且中心处陶瓷膜厚度随电极距离的增大迅速减小,电能利用率随之降低.
关键词:
微弧氧化
约束阴极
放电特性
电极间距 相似文献
18.
The problem of the potential distribution in a plane vacuum diode is solved for arbitrary values of the space charge density
and the initial electron velocity. The resultant solution makes it possible to study the conditions for the potential minimum
appearing near the cathode, to determine the position and depth of this minimum, to derive analytic formulas for the potential
distribution in the entire space between the cathode and the anode, and to analyze the problem of an infinitely high space
charge density. 相似文献
19.
I. A. Krinberg 《Technical Physics》2001,46(11):1371-1378
A general solution to the problem of the steady-state spherical expansion of a current-carrying multicomponent plasma into
a vacuum is derived. It is shown that, in vacuum arc discharges, the main force accelerating the cathode material, which becomes
a plasma at distances of 1 to 300 μm from the cathode surface, is the electron pressure gradient force maintained by Joule
heating. It is established that ions of different charges move with the same hydrodynamic velocity, which is uniquely determined
by the mass and mean charge of the ions and the maximum electron temperature in the cathode region. 相似文献