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4 Aug 2008

Volume 93, Issue 5, Articles (05xxxx)

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Appl. Phys. Lett. 93, 051101 (2008); http://dx.doi.org/10.1063/1.2965797 (3 pages)

Mariano A. Zimmler, Jiming Bao, Federico Capasso, Sven Müller, and Carsten Ronning
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Microwave plasma torch operating in a chamber at a low pressure

Han S. Uhm, Soon C. Cho, and Yong C. Hong

Appl. Phys. Lett. 93, 051501 (2008); http://dx.doi.org/10.1063/1.2965459 (3 pages) | Cited 1 time

Online Publication Date: 5 August 2008

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A microwave plasma torch was operated in a chamber at a reduced pressure, and the properties of the torch plasma were investigated. The argon torch plasma at a reduced pressure of 150 Torr was observed to be well diffused in the discharge tube instead of the filamentary structures at the atmospheric pressure. The typical torch plasma density and electron temperature are measured to be ne = 2×1014/cm3 and Te = 1.5 eV, respectively, for argon plasmas at 150 Torr. It was also found that the microwave plasma torch at a low pressure may efficiently produce chemical radicals.
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52.75.Hn Plasma torches
52.80.-s Electric discharges
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)

The multipole resonance probe: A concept for simultaneous determination of plasma density, electron temperature, and collision rate in low-pressure plasmas

M. Lapke, T. Mussenbrock, and R. P. Brinkmann

Appl. Phys. Lett. 93, 051502 (2008); http://dx.doi.org/10.1063/1.2966351 (3 pages) | Cited 9 times

Online Publication Date: 6 August 2008

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A diagnostic concept is presented which enables the simultaneous determination of plasma density, electron temperature, and collision rate in low-pressure gas discharges. The proposed method utilizes a radio-frequency driven probe of particular spherical design which is immersed in the plasma to excite a family of spatially bounded surface resonances. An analysis of the measured absorption spectrum S(ω) of the probe provides information on the distribution of the plasma in its vicinity, from which the values of the plasma parameters can be inferred. In its simplest realization, the probe consists of two dielectrically shielded, conducting hemispheres, which are symmetrically driven by an radio-frequency source, and the excited resonances can be classified as multipole fields, which allows an analytical evaluation of the measured signal. The proposed method is robust, calibration free, economical, and can be used for ideal and reactive plasmas alike.
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52.70.Gw Radio-frequency and microwave measurements
52.25.-b Plasma properties
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
52.20.Fs Electron collisions

Radio-frequency power assistance on a compact magnetohydrodynamic electrical power generator under high-density magnetic flux

Tomoyuki Murakami and Yoshihiro Okuno

Appl. Phys. Lett. 93, 051503 (2008); http://dx.doi.org/10.1063/1.2969044 (3 pages) | Cited 7 times

Online Publication Date: 7 August 2008

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We describe the effect of radio-frequency (rf) electromagnetic field application on a compact magnetohydrodynamic (MHD) electrical power generator under high-density magnetic flux. The rf-power assistance improves the Hall potential profile and fluid flow structure, and rectifies large-scale plasma instability. These effects are vital for the compact MHD generator. With the aid of rf power, the power generation performance is significantly improved even under the low-plasma-stability condition for high-density magnetic flux.
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84.60.Lw Magnetohydrodynamic conversion
96.25.St Plasma and MHD instabilities
94.30.C- Magnetospheric configuration and dynamics

Atmospheric pressure nitrogen plasma jet: Observation of striated multilayer discharge patterns

Yong Cheol Hong, Han Sup Uhm, and Won Ju Yi

Appl. Phys. Lett. 93, 051504 (2008); http://dx.doi.org/10.1063/1.2969287 (3 pages) | Cited 16 times

Online Publication Date: 7 August 2008

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This paper presents a nitrogen microplasma jet that operates at atmospheric pressure and provides details of an observation of the striated multilayer discharge patterns formed in the plasma jet. The plasma jet device in a microhollow electrode is a pencil-type configuration that produces a long cold plasma jet capable of reaching 3.5 cm and having various excited plasma species shown through optical emission spectrum. By introducing a gas flow rate of more than 5 l/min, striated discharge patterns in the plasma jet are produced through ionization wave propagation.
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52.75.-d Plasma devices
52.80.-s Electric discharges

Titanium dioxide nanofiber-cotton targets for efficient multi-keV x-ray generation

Minoru Tanabe, Hiroaki Nishimura, Shinsuke Fujioka, Keiji Nagai, Norimasa Yamamoto, Zhong-Ze Gu, Chao Pan, Frederic Girard, Michel Primout, Bruno Villette, Didier Brebion, Kevin B. Fournier, Akira Fujishima, and Kunioki Mima

Appl. Phys. Lett. 93, 051505 (2008); http://dx.doi.org/10.1063/1.2969300 (3 pages) | Cited 6 times

Online Publication Date: 7 August 2008

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Multi-keV x-ray generation from low-density (27±7 mg/cm3) nanofiber-cotton targets composed of titanium dioxide has been investigated. The cotton targets were heated volumetrically and supersonically to a peak electron temperature of 2.3 keV, which is optimal to yield Ti K-shell x rays. Considerable enhancement of conversion efficiency [(3.7±0.5)%] from incident laser energy into Ti K-shell x rays (4–6 keV band) was attained in comparison with that [(1.4±0.9)%] for a planar Ti-foil target.
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52.38.Ph X-ray, γ-ray, and particle generation
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
52.70.La X-ray and γ-ray measurements

Femtosecond laser-induced electronic plasma at metal surface

Zhaoyang Chen and Samuel S. Mao

Appl. Phys. Lett. 93, 051506 (2008); http://dx.doi.org/10.1063/1.2966152 (3 pages) | Cited 11 times

Online Publication Date: 8 August 2008

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We develop a theoretical analysis to model plasma initiation at the early stage of femtosecond laser irradiation of metal surfaces. The calculation reveals that there is a threshold intensity for the formation of a microscale electronic plasma at the laser-irradidated metal surface. As the full width at half maximum of a laser pulse increases from 15 to 200 fs, the plasma formation threshold decreases by merely about 20%. The dependence of the threshold intensity on laser pulse width can be attributed to laser-induced surface electron emission, in particular due to the effect of photoelectric effect.
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52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
79.20.Ds Laser-beam impact phenomena
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