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15 Oct 2010

Volume 108, Issue 8, Articles (08xxxx)

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J. Appl. Phys. 108, 081101 (2010); http://dx.doi.org/10.1063/1.3493111 (18 pages)

Yiping Wang
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back to top Plasmas and Electrical Discharges

Suppression of current fluctuations in an intense electron beam

J. R. Harris and J. W. Lewellen

J. Appl. Phys. 108, 083301 (2010); http://dx.doi.org/10.1063/1.3468176 (5 pages) | Cited 1 time

Online Publication Date: 19 October 2010

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When an intense beam encounters an aperture, the transmitted current depends on the properties of the beam and the transport channel, as well as those of the aperture itself. In some cases, an increase in the incident beam current will be exactly compensated by an increase in the incident beam area, so that the current density at the aperture remains unchanged. When this occurs, the transmitted beam current becomes independent of changes in the incident beam current, providing a passive means for suppressing current fluctuations in the beam. In this article, a key requirement for the existence of this condition is derived. This requirement is shown to be fulfilled in the case of an idealized uniform focusing channel in the small-signal limit, but to be violated when the current fluctuations are not small. Even in this case, the apertured transport system retains the ability to suppress—but not totally eliminate—fluctuations in the transmitted beam current for a wide range of incident beam currents.
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41.85.Lc Particle beam focusing and bending magnets, wiggler magnets, and quadrupoles

Optical and electrical characterization of pulse-modulated argon atmospheric-pressure inductively coupled microplasma jets

Satomi Tajima, Masashi Matsumori, Shigeki Nakatsuka, Shouichi Tsuchiya, and Takanori Ichiki

J. Appl. Phys. 108, 083302 (2010); http://dx.doi.org/10.1063/1.3499272 (5 pages) | Cited 1 time

Online Publication Date: 21 October 2010

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The critical parameters determining the generation of the pulse-modulated argon atmospheric-pressure inductively coupled plasma (AP-ICP) microjet were studied by varying the power, P, pulse-modulation frequency, f, and duty ratio, DR. The temporal changes in the net output power, Pnet, monitored between the very high frequency power supply and matching network by an rf sampler, and ArI 4s′[1/2]1O–4p′[1/2]0 emission from the antenna were measured to elucidate the behavior of this plasma. The AP-ICP microjet, which produces high-density (0.9–1.1×1015 cm−3) nonequilibrium plasma, consists of an alumina discharge tube with the inner diameter of 0.8 mm. The generation diagram of the pulse-modulated plasma was created by having f as the horizontal axis and DR as the vertical axis while varying P up to 50 W. At f ≤ 10 kHz, the plasma was generated at above the linear lines of f and DR, which indicated the existence of the critical power-off period of approximately 80 μs. At f>10 kHz, the pulse-modulated plasma was produced above constant DR and almost independent of f. The time-averaged power, math, which is the product of P and DR, had to be more than 8–10 W to sustain the pulse-modulated plasma. From the measurement of the temporal changes in the net power and ArI emission, the dynamic behavior of the pulse-modulated plasma was revealed as follows. The prebreakdown period was present for ∼ 5 μs after the power was turned on. Once the plasma was generated, the impedance was changed and the reflected power gradually decreased. A strong emission peak was observed immediately after the breakdown, followed by the gradual increase up to the steady state. Finally, the intense afterpeak was observed at 0.8 μs after the power was turned off.
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52.75.-d Plasma devices
52.25.Kn Thermodynamics of plasmas
52.40.Fd Plasma interactions with antennas; plasma-filled waveguides
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.70.Ds Electric and magnetic measurements
52.70.Kz Optical (ultraviolet, visible, infrared) measurements

Nanowire charging in collisionless plasma

Anaram Shahravan, Chris Lucas, and Themis Matsoukas

J. Appl. Phys. 108, 083303 (2010); http://dx.doi.org/10.1063/1.3483300 (7 pages) | Cited 1 time

Online Publication Date: 27 October 2010

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We calculate the collision cross section of a charged finite cylinder (nanowire) with a beam of ions and electrons in collisionless plasma. We find that, while the shape and area of the cross section has complex dependence on the charge and orientation of the nanowire relative to the charged beam, its orientational average has a remarkably simple form: for attractive interactions, it is a linear function of the electrostatic ratio qjqpe2/4πϵ0L0kT, where qje is the charge of the ions/electrons, qpe is the charge on the cylinder, L0 is the half-length of the nanowire, T is the temperature of the charged species, and ϵ0 is the permittivity of free space. This linearity persists into the repulsive regime up until the cross sectional area is reduced to about 5% of its value for neutral collisions. We calculate the corresponding charging currents and show that the charging behavior of the nanowire in Maxwellian plasma is described by an equivalent sphere whose radius depends only on the aspect ratio of the nanowire. For small aspect ratios, the equivalent sphere has the same surface area as the nanowire.
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52.27.Lw Dusty or complex plasmas; plasma crystals
52.20.Fs Electron collisions
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)
73.63.Nm Quantum wires
52.25.-b Plasma properties
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