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15 Dec 2010

Volume 108, Issue 12, Articles (12xxxx)

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J. Appl. Phys. 108, 121101 (2010); http://dx.doi.org/10.1063/1.3503505 (12 pages)

J. Martin, T. Tritt, and C. Uher
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back to top Plasmas and Electrical Discharges

Modeling electron flow produced by a three-dimensional spatially periodic field emitter

A. Rokhlenko and J. L. Lebowitz

J. Appl. Phys. 108, 123301 (2010); http://dx.doi.org/10.1063/1.3520672 (6 pages) | Cited 1 time

Online Publication Date: 17 December 2010

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We study the space charge limited field emission from an emitter whose surface has a simple periodic structure with bumps. The shape of each bump is represented by a smooth function and the emission is governed by the Fowler–Nordheim–Schottky law. A mathematical scheme for modeling the potential and current structure by a set of elementary functions is developed and implemented numerically with the help of a special least square procedure. Our results show that such emitters are more efficient than emitters with long ridges only in weak electric fields. In stronger fields the latter give larger currents and they should be more durable. The emission by an individual bump in our periodic structure is compared also with that of a single emitter bump of the same shape, they appear to be quite close.
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85.45.Db Field emitters and arrays, cold electron emitters
85.45.Bz Vacuum microelectronic device characterization, design, and modeling
79.70.+q Field emission, ionization, evaporation, and desorption

Self-field effects on instability of wave modes in a free-electron laser with background plasma

Atefeh Ghazavi, Behrouz Maraghechi, and Taghi Mohsenpour

J. Appl. Phys. 108, 123302 (2010); http://dx.doi.org/10.1063/1.3520664 (7 pages) | Cited 1 time

Online Publication Date: 21 December 2010

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A dispersion relation for the plasma loaded free-electron laser (FEL), with a helical wiggler and an axial magnetic field is derived. The cold fluid formulation is used with self-fields of the electron beam taken into account. By solving the dispersion relation numerically the influence of self-fields on the FEL resonance and the two-stream instability is investigated. It was found that although self-fields have strong effect on the FEL resonance, their effects on the two-stream instability is much weaker.
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41.60.Cr Free-electron lasers
41.75.Ht Relativistic electron and positron beams
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Excitation of terahertz plasmons eigenmode of a parallel plane guiding system by an electron beam

Pawan Kumar, Manish Kumar, and V. K. Tripathi

J. Appl. Phys. 108, 123303 (2010); http://dx.doi.org/10.1063/1.3524368 (4 pages) | Cited 2 times

Online Publication Date: 23 December 2010

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Two parallel semiconductor plates, separated by a short distance, support surface plasmon eigenmode with amplitude maxima at the inner surfaces of the plates and minimum at the center. A relativistic sheet electron beam propagating through the space between the planes resonantly excites the surface plasma wave (SPW). The frequency of the driven SPW decreases with the energy of the beam while the growth rate increases. At the beam current ≈168 A the growth rate of 5.93×108 rad/s is achieved at the frequency ≈0.51 THz of SPW for the 5 mm math width and spacing between the two plates of ≈2.83 mm. The growth rate scales as 1/3 root of the electron beam current.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Electrical double layers at shock fronts in glow discharges and afterglows

Nicholas S. Siefert

J. Appl. Phys. 108, 123304 (2010); http://dx.doi.org/10.1063/1.3511745 (11 pages)

Online Publication Date: 28 December 2010

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This paper examines the propagation of spark-generated shockwaves (1.0<Mach<2.0) into argon and nitrogen glow discharges and their afterglow. Diagnostic methods were employed and expanded in order to capture the dynamics of the shock front in these weakly-ionized, nonmagnetized, collisional plasmas. We used a microwave hairpin resonator to measure the electron number density, and, for all cases, we measured an increase in the electron number density at the shock front. By comparing the increase in electron number density at the shock front in the active discharge and in the afterglow, we conclude that electrons with a temperature much greater than room temperature can be compressed at the shock front. The ratio of electron number density before and after the shock front can be approximately predicted using the Rankine–Hugoniot relationship. The large gradient in electron density, and hence a large gradient in the flux of charged species, created a region of space-charge separation, i.e., a double layer, at the shock front. The double layer balances the flux of charged particles on both sides of the shock front. The double layer voltage drop was measured in the current-carrying discharge using floating probes and compared with previous models. As well, we measured argon 1s5 metastable-state density and demonstrate that metastable-state neutral species can be compressed across a shock front and approximately predicted using the Rankine–Hugoniot relationship.
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52.35.Tc Shock waves and discontinuities
52.80.Hc Glow; corona
52.80.Mg Arcs; sparks; lightning; atmospheric electricity
52.25.-b Plasma properties
52.70.Ds Electric and magnetic measurements

Microwave air plasma source at atmospheric pressure: Experiment and theory

E. Tatarova, F. M. Dias, E. Felizardo, J. Henriques, M. J. Pinheiro, C. M. Ferreira, and B. Gordiets

J. Appl. Phys. 108, 123305 (2010); http://dx.doi.org/10.1063/1.3525245 (18 pages) | Cited 3 times

Online Publication Date: 29 December 2010

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An experimental and theoretical investigation of the axial structure of a surface wave (2.45 GHz) driven atmospheric plasma source in air with a small admixture (1%) of water vapor has been performed. Measurements of the gas temperature and of the intensities of the O(777.4 nm), O(844.6 nm), and O(630 nm) atomic lines and the NO(γ) molecular band versus input power and axial position were carried out. Amplitude and phase sensitive measurements have also been performed to derive the surface wave dispersion characteristics. The experimental results are analyzed in terms of a one-dimensional theoretical model based on a self-consistent treatment of particle kinetics, gas dynamics, and wave electrodynamics. The predicted gas temperature and emission line intensities variations with power and axial position are shown to compare well with experiment. “Hot” excited O atoms (with kinetic energy ∼ 2 eV) have been detected.
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52.50.Dg Plasma sources
52.25.Dg Plasma kinetic equations
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.25.Os Emission, absorption, and scattering of electromagnetic radiation

Compression and strong rarefaction in high power impulse magnetron sputtering discharges

David Horwat and André Anders

J. Appl. Phys. 108, 123306 (2010); http://dx.doi.org/10.1063/1.3525986 (6 pages) | Cited 15 times

Online Publication Date: 29 December 2010

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Gas compression and strong rarefaction have been observed for high power impulse magnetron sputtering (HIPIMS) discharges using a copper target in argon. Time-resolved ion saturation currents of 35 probes were simultaneously recorded for HIPIMS discharges operating far above the self-sputtering runaway threshold. The argon background pressure was a parameter for the evaluation of the spatial and temporal development of the plasma density distribution. The data can be interpreted by a massive onset of the sputtering flux (sputter wind) that causes a transient densification of the gas, followed by rarefaction and the replacement of gas plasma by the metal plasma of sustained self-sputtering. The plasma density pulse follows closely the power pulse at low pressure. At high pressure, the relatively remote probes recorded a density peak only after the discharge pulse, indicative for slow, diffusive ion transport.
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52.80.Sm Magnetoactive discharges (e.g., Penning discharges)
52.25.Fi Transport properties
52.70.Ds Electric and magnetic measurements
52.40.Hf Plasma-material interactions; boundary layer effects
52.50.Dg Plasma sources
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