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1.
Multi-pulsed intense electron beam emission from velvet,carbon fibers,carbon nano-tubes and dispenser cathodes
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XIA Lian-Sheng YANG An-Min CHEN Yi ZHANG Huang LIU Xing-Guang LI Jin JIANG Xiao-Guo ZHANG Kai-Zhi SHI Jin-Shui DENG Jian-Jun ZHANG Lin-Wen 《中国物理C(英文版)》2010,34(11):1733-1737
The experimental results of studies of four kinds of cathode emitting intense electron beams are demonstrated under multi-pulsed mode based on an experimental setup including two multi-pulse high voltage sources.The tested cathodes include velvet,carbon fibers,carbon nano-tubes(CNTs)and dispenser cathodes.The results indicate that all four are able to emit multi-pulsed beams.For velvet,carbon fiber and CNTs,the electron induced cathode plasma emission may be the main process and this means that there are differences in beam parameters from pulse to pulse.For dispenser cathodes tested in the experiment,although there is a little difference from pulse to pulse for some reason,thermal-electric field emission may be the main process. 相似文献
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Ya E. Krasik K. Chirko J. Z. Gleizer A. Krokhmal A. Dunaevsky J. Felsteiner 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,19(1):89-95
In this paper the parameters of two types of high-current switches based on ferroelectric BaTiO3 ignition are presented. Both types of switches showed a reliable and controllable operation with a repetition rate of several
Hz. The first type is a vacuum two-electrode switch ignited by the plasma which is generated by a BaTiO3 cathode. This type of switch was tested in the voltage range of 3-25 kV and switched current amplitude of 2-15 kA with either
negative or positive polarity of the high-voltage electrode. The second type is a BaTiO3 surface flashover strip-like switch ignited by a driving pulse which has an amplitude of several kV. It was shown that the
application of the driving pulse (>10 kV) leads to the appearance of many non-complete surface discharges which transform
further to a multi-channel discharge. This type of switch was tested in the voltage range of 1-25 kV and current amplitude
of 0.5-15 kA. The design of the switches, their lifetime, the time jitter and the parameters of the switched current for different
discharge conditions are presented.
Received 5 November 2001 相似文献
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M.G. Donato G. Faggio M. Marinelli G. Messina E. Milani A. Paoletti S. Santangelo A. Tucciarone G. Verona Rinati 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,20(1):133-139
High quality synthetic diamonds were grown on single-crystal silicon by microwave plasma enhanced chemical vapour deposition
(CVD). A careful optimisation of both the experimental setup and the growth parameters was necessary before that the achievement
of the best results was made possible. The films were deposited using a CH4-H2 gas mixture at methane concentrations variable in the range 0.6-2.2%, while the substrate temperature was fixed at 750 °C. Raman spectroscopy and photoluminescence (PL) were utilised to monitor the quality of the deposited films and to study
the spatial distribution of defects, respectively. Micro-Raman analysis shows that linewidths of the diamond peak lower than
2.4 cm-1 can be easily measured at the growth surface, indicating that the crystalline quality of individual grains is comparable
to that of the best natural diamonds. The excellent phase purity of the diamond microcrystals at the growth surface is witnessed
by the complete absence of any non-diamond carbon feature and by a very weak luminescence background in the 1.6-2.4 eV spectral
range. A worsening of the quality of the diamond particles is found moving from the growth surface towards the film-substrate
interface. A photoluminescence feature at about 1.68 eV, commonly associated to Si impurities, is distinctly observed as the
exciting laser beam is focused close to the interface. A progressive degradation of the global quality of the films is found
with increasing methane concentration in the gas mixture, as witnessed by an increased PL background in the films grown at
higher methane concentrations.
Received 24 November 2000 相似文献
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Shiffler D. LaCour M. Golby K. Sena M. Mithcell M. Haworth M. Hendricks K. Spencer T. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》2001,29(3):445-451
Presents results of an experimental comparison of a velvet cathode- and a carbon fiber cathode-coated with cesium iodide (CsI) salt. Each cathode had a planar geometry, with similar emission areas. The cathodes were tested at electric field strengths of 50 kV/cm at anode-cathode (A-K) gaps of 4.0 cm. The applied voltage had a 1-μs duration and the pulser was operated at up to a 1-Hz repetition rate. The system had a low base pressure (<1.0×10-7 torr). This paper reports the results and comparisons of experiments on each cathode. We address the current and voltage characteristics, the shot-to-shot reproducibility, the pressure evolution of the diode under 1-Hz operation, and the lifetime of the cathodes 相似文献
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E. Neumann A. Pikovsky 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(2):219-228
We consider the dynamics of the overdamped Josephson junction under the influence of an external quasiperiodic driving field.
In dependence on parameter values either a quasiperiodic motion or a strange nochaotic attractor (SNA) can be observed. The
latter corresponds to a resistive state in the current-voltage characteristics while for quasiperiodic motion a finite superconducting
current exists for zero voltage. It is shown that in the case of SNA a nonzero mean voltage across the junction can appear
due to symmetry breakings. Based on this observation a detailed symmetry consideration of the generalized equation of motion
is performed and symmetry conditions ensuring zero mean voltage across the junction are found.
Received 16 August 2001 and Received in final form 22 January 2002 相似文献
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Hong-Kang Zhao 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,33(3):365-372
The ac Stark effect is investigated in the toroidal carbon nanotube system threaded with an ac magnetic flux. The Floquet
theory is employed to deal with the time-dependent quantum problems. The time-averaged energy of the system is derived and
is found to exhibit a strong relationship with an external field, and the modified energy gap has been presented. The ac flux
enhances energy gaps to cause metal-semiconductor transition. The steady current has been obtained by employing the free energy
approach, and the persistent current is a special case as the magnitude of the ac flux approaches zero. The photon-assisted
current is quite different from the persistent current due to the absorption and emission of photons. The local density of
states is obtained by calculating the Green's function in the Floquet state, and photon-resonant structures are observed.
All of the novel features are associated with the ac Stark effect, which is caused by the modification of energy levels.
Received 20 November 2002 / Received in final form 7 February 2003 Published online 20 June 2003
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ID="a"e-mail: zhaohonk@yahoo.com 相似文献
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Turchi P.J. Peterkin R.E. Jr 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1998,26(5):1485-1491
Electron-beam diodes driven by fast-rising, high-voltage pulses often operate with cold cathodes for which the presence of a plasma adjacent to the cathode surface is essential to obtain adequate electron emission. A consequence of such surface plasma, however, is closure of the interelectrode gap by plasma motion. Resistive heating of the plasma competes with work performed in expanding the plasma and heat transfer to the cold-cathode boundary. The resulting closure speed is calculated, using an MHD code, and found to agree well with results of experiments using organic-cloth cathodes at 35 kV. Computed plasma speeds are typically 8-12 km/s, and are relatively insensitive to the applied voltage. Gap closure due to the plasma motion calculated numerically corresponds to estimates based on impedance collapse in the experiments 相似文献
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M. Beuve M. Caron B. Gervais H. Rothard A. Clouvas C. Potiriadis 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,15(3):293-300
It is usually well accepted that for swift protons, the induced backward and forward electron emission yield is proportional
to the projectile electronic stopping power. This was observed in particular for thin amorphous carbon foils. However, this
law was established from a non extensive set of experimental data and somewhat confirmed by rough macroscopic theories. We
then developed a standard Monte Carlo simulation to predict the yield dependence on proton energy [0.5–10 MeV] and for a wide
range of foil thickness. After evaluating the reliability of this simulation, we showed and explained why the law of proportionality
cannot generally hold for forward electron emission. In particular, the ratio between forward yield and stopping power generally
depends on foil thickness and proton energy. We performed a new experiment that confirmed our theoretical predictions.
Received 9 March 2001 相似文献
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采用电泳沉积法、碳纳米管纸和化学气相沉积直接生长法制备了三种碳纳米管阴极. 从强流发射性能、阴极等离子体膨胀、阴极起动、发射均匀性、工作稳定性以及脉冲放气特性等多个方面, 对比研究了碳纳米管阴极和化纤天鹅绒阴极的强流发射特性, 研究表明碳纳米管阵列和碳纳米管纸阴极发射性能明显优于普通化纤天鹅绒, 碳纳米管阴极发射性能与碳纳米管取向无关, 管壁的缺陷发射对无序碳纳米管阴极强流发射具有重要贡献. 碳纳米管阴极的起动场强约为普通化纤天鹅绒的2/3, 电场上升率相同时碳纳米管阴极比化纤天鹅绒阴极起动时间短12–17 ns. 碳纳米管阴极发射均匀性优于化纤天鹅绒, 尤其是碳纳米管阵列, 整个阴极表面等离子体光斑致密且均匀. 在二极管本底气压为6×10-3 Pa时, 碳纳米管纸阴极对应的二极管峰值气压不到0.3 Pa, 约为普通化纤天鹅绒阴极的1/5, 碳纳米管阵列阴极放气量在三种阴极中最少, 仅为0.042 Pa. 结果表明, 碳纳米管阴极在强流电子束源和相关高功率微波器件领域具有潜在的应用价值. 相似文献
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D. Bernardi V. Colombo G.G.M. Coppa A. D'Angola 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,14(3):337-348
The paper deals with the time-dependent numerical simulation of inductively-coupled plasma torches during the ignition transient,
which is induced by a graphite rod and leads to the final, self-sustaining plasma condition. The study has been performed
by using a 2D time-dependent fluid-magnetic code based on the SIMPLER algorithm within the assumptions of laminar flow, local
thermodynamic equilibrium conditions and optically thin plasma. The graphite rod has been treated as a real obstacle for the
gas and the electron emission due to the thermoionic effect has been suitably taken into account. The advantage of using a
time-dependent code in order to select different plasma operating conditions that can lead to stable discharges is pointed
out. Results for both argon and air discharges are presented for different torch geometries, RF frequencies and inlet gas
configurations (also including the presence of a carrier gas injected along the axis of the torch). Moreover, the final self-sustaining
plasma configurations obtained are compared, when available, with results coming from static models, which have been published
by other authors.
Received 29 December 2000 相似文献
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This paper mainly investigates plasma characterization on carbon
fiber cathodes with and without cesium iodide (CsI) coating powered
by a ~300~ns, ~ 200~kV accelerating pulse. It was found
that the CsI layers can not only improve the diode voltage, but also
maintain a stable perveance. This indicates a slowly changed diode
gap or a low cathode plasma expansion velocity. By spectroscopic
diagnostics, in the vicinity of the cathode surface the average
plasma density and temperature were found to be ~ 3×
1014~cm-3 and ~ 5~eV, respectively, for an
electron current density of ~ 40~A/cm2. Furthermore, there
exists a multicomponent plasma expansion toward the anode. The
plasma expansion velocity, corresponding to the carbon and hydrogen
ions, is estimated to be ~ 1.5~cm/μ s. Most notably, Cs
spectroscopic line was obtained only at the distance ≤ 0.5~mm
from the cathode surface. Carbon and hydrogen ions are obtained up
to the distance of 2.5~mm from the cathode surface. Cs ions almost
remain at the vicinity of the cathode surface. These results show
that the addition of CsI enables a slow cathode plasma expansion
toward the anode, providing a positive prospect for developing
long-pulse electron beam sources. 相似文献
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Al.A. Zakhidov R. Nanjundaswamy A.N. Obraztsov M. Zhang S. Fang V.I. Klesch R.H. Baughman A.A. Zakhidov 《Applied Physics A: Materials Science & Processing》2007,88(4):593-600
Field emission with high current density at low operating voltage was found for the yarns obtained by solid state spinning
process from forest of vertically aligned multiwall carbon nanotubes. The nanotube forest was produced catalytically by CVD
method. It is found that only a small fraction of carbon nanotubes from their total amount in the yarn yields to electron
emission from its free end. This led to resistive heating of the emitting tubes and limiting of the emission current. The
field emission microscopy pictures of MWNT yarn in free-end geometry appears to be very different from that of the conventional
non-yarn carbon nanotube-based cathodes described in all previous studies. The FEM patterns are found to consist of the set
of line and arc segments rather than a set of spots. Possible explanation of this effect is presented and discussed. The field
emission from the lateral side of the yarns showed the self-enhanced currents increasing with operation time. We assume that
this current increase may be due to untwisting and unwrapping of yarns resulted of application of the electric field. The
lowest threshold field of about 0.7 V/μm was obtained after a few cycles of applied field increase. The prototypes of cathodoluminescent
lamps and alphanumerical indicators based on MWNT twist-yarn cold cathodes are demonstrated.
PACS 79.70.+q; 61.46.Fg; 85.45.Db 相似文献
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A. Komnik R. Egger 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(2):271-280
We study nonlinear transport for two coupled one-dimensional quantum wires or carbon nanotubes described by Luttinger liquid
theory. Transport properties are shown to crucially depend on the contact length L
c. For a special interaction strength, the problem can be solved analytically for arbitrary L
c. For point-like contacts and strong interactions, a qualitatively different picture compared to a Fermi liquid emerges, characterized
by zero-bias anomalies and strong dependence on the applied cross voltage. In addition, pronounced Coulomb drag phenomena
are important for extended contacts.
Received 28 July 2000 相似文献
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Shiffler D.A. LaCour M.J. Sena M.D. Mitchell M.D. Haworth M.D. Hendricks K.J. Spencer T.A. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》2000,28(3):517-522
Presents results of an experimental comparison of a bare carbon fiber cathode and the same cathode when coated with cesium iodide salt (CsI). An annular cathode was constructed by arranging carbon fibers in an annular tuft pattern. The cathode was then operated as a bare carbon fiber cathode and in a configuration with a CsI coating. The cathode was tested at electric field strengths ranging from 50 kV/cm to 265 kV/cm at anode-cathode (A-K) gaps of 3.175 cm. The applied voltage had a 1-μs duration and the modulator was operated at up to 1 Hz repetition rate. The system had a low base pressure (<1.0×10-7 torr). The article reports on results concerning the conditioning of the cathodes, the shot-to-shot reproducibility of the cathodes and the pressure evolution of the diode under 1 Hz operation. We also report on the impedance evolution of each of the diodes 相似文献
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Electron emission from nano-patterned amorphous carbon is realized in this paper. The patterned carbon consists of islands with size of tens of nanometers, and is formed by etching uniform carbon film in oxygen plasma using a bismuth island-like film as the mask. Uniform and stable electron emission is reproducibly obtained, and the emission efficiency is above 2% at an anode voltage of 3 kV. Small carbon particles between large islands are supposed to be necessary for stable electron emission. 相似文献
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V. Milosavljević S. Djeniže 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,23(3):385-390
On the basis of the precisely recorded 706.52 nm He I line shape we have obtained the basic plasma parameters i.e. electron temperature (T) and electron density (N) using our new line deconvolution procedure in the case of five various plasmas created in a linear, low-pressure, pulsed
arc discharge. Plasma parameters have been also measured using independent experimental diagnostical techniques. Excellent
agreement was found among the two sets of the obtained parameters. This enables our deconvolution procedure to recommendation
for plasma diagnostical purposes, especially in astrophysics where direct measurements of the plasma parameters (T and N) are not possible. Besides, on the basis of the observed asymmetry of the Stark broadened line profile we have obtained its
ion broadening parameter (A) caused by influence of the ion microfield to the line broadening mechanism 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 using the line profile deconvolution procedure. We have found
stronger influence of the ion contribution to the 706.52 nm He I line profile than the existing theoretical approximations
estimate. This can be important for plasma modeling or for diagnostics.
Received 30 October 2002 Published online 15 April 2003
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ID="a"e-mail: vladimir@ff.bg.ac.yu 相似文献