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15 Nov 2007

Volume 102, Issue 10, Articles (10xxxx)

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High energy pulsed inductive thruster modeling operating with ammonia propellant

Pavlos G. Mikellides and James K. Villarreal

J. Appl. Phys. 102, 103301 (2007); http://dx.doi.org/10.1063/1.2809436 (8 pages) | Cited 4 times

Online Publication Date: 16 November 2007

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Numerical modeling of the pulsed inductive thruster operating with ammonia propellant at high energy levels, utilized a time-dependent, two-dimensional, and axisymmetric magnetohydrodynamics code to provide bilateral validation of experiment and theory and offer performance insights for improved designs. The power circuit model was augmented by a plasma voltage algorithm that accounts for the propellant’s time-dependent resistance and inductance to properly account for plasma dynamics and was verified using available analytic solutions of two idealized plasma problems. Comparisons of the predicted current waveforms to experimental data exhibited excellent agreement for the initial half-period, essentially capturing the dominant acceleration phase. Further validation proceeded by comparisons of the impulse for three different energy levels, 2592, 4050, and 4608 J and a wide range of propellant mass values. Predicted impulse captured both trends and magnitudes measured experimentally for nominal operation. Interpretation of the modeling results in conjunction to experimental observations further confirm the critical mass phenomenon beyond which efficiency degrades due to elevated internal energy mode deposition and anomalous operation.
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52.75.Di Ion and plasma propulsion
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.65.Kj Magnetohydrodynamic and fluid equation
02.60.Cb Numerical simulation; solution of equations

Laser-induced breakdown spectroscopy of trisilane using infrared CO2 laser pulses

J. J. Camacho, J. M. L. Poyato, L. Díaz, and M. Santos

J. Appl. Phys. 102, 103302 (2007); http://dx.doi.org/10.1063/1.2811870 (10 pages) | Cited 5 times

Online Publication Date: 20 November 2007

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The plasma produced in trisilane (Si3H8) at room temperature and pressures ranging from 50 to 103 Pa by laser-induced breakdown (LIB) has been investigated. The ultraviolet-visible-near infrared emission generated by high-power IR CO2 laser pulses in Si3H8 has been studied by means of optical emission spectroscopy. Optical breakdown threshold intensities in trisilane at 10.591 μm for laser pulse lengths of 100 ns have been measured as a function of gas pressure. The strong emission observed in the plasma region is mainly due to electronic relaxation of excited atomic H and Si and ionic fragments Si+, Si2+, and Si3+. An excitation temperature Texc = 5600±300 K was calculated by means of H atomic lines assuming local thermodynamic equilibrium. The physical processes leading to LIB of trisilane in the power density range 0.28 GW cm−2<J<3.99 GW cm−2 have been analyzed. From our experimental observations we can propose that, although the first electrons must appear via multiphoton ionization, electron cascade is the main mechanism responsible for the breakdown in trisilane.
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78.55.Hx Other solid inorganic materials

Practical sensor for nitrogen in direct current glow discharges

D. Popović, V. Milosavljević, and S. Daniels

J. Appl. Phys. 102, 103303 (2007); http://dx.doi.org/10.1063/1.2816254 (7 pages) | Cited 3 times

Online Publication Date: 29 November 2007

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This paper presents a method for precise measurement of atomic and molecular nitrogen in an oxygen-nitrogen dc plasma. This is achieved by monitoring the intensities of the atomic nitrogen spectral line at 821.6 nm and the molecular nitrogen bandhead at 337.1 nm, relative to the atomic oxygen spectral line at 844.7 nm. Oxygen is one of the most frequently used gases for surface chemical treatment, including deposition and etching, therefore the ability to measure and control the process and chemical composition of the process is essential. To validate this oxygen actimometry method for N2-xO2 (where x varies from 0 to 1) dc plasmas, threshold tests have been performed with Ar actinometry. The optical measurements have been performed using two methods. The first approach uses a USB2000 fiber optic spectrometer, calibrated with a Gigahertz–Optik BN-0102-1 reference standard source, to record the desired spectral lines. The second approach uses narrow bandwidth optical filters ( ∼ 0.7–0.07 nm) with central wavelengths of 821.6, 337.1, and 844.69 nm and photodiodes to detect the emission intensity, also calibrated with the same standard source. Optical data are collected for a range of experimental conditions in a flowing glow discharge of N2-xO2 mixture. The maximum dc voltage is 2.2 kV and maximum chamber pressure is 266 Pa. Data from both optical methods are compared and used to interpret the relative atomic and molecular nitrogen concentrations under various operating conditions.
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82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
52.80.Hc Glow; corona

A double-band high-power microwave source

Yu-Wei Fan, Hui-Huang Zhong, Zhi-Qiang Li, Ting Shu, Jian-De Zhang, Jun Zhang, Xiao-Ping Zhang, Jian-Hua Yang, and Ling Luo

J. Appl. Phys. 102, 103304 (2007); http://dx.doi.org/10.1063/1.2817254 (3 pages) | Cited 12 times

Online Publication Date: 29 November 2007

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In order to increase the power conversion efficiency of a magnetically insulated line oscillator (MILO), an axially extracted virtual cathode oscillator (VCO) is introduced to utilize the load current in the MILO, so it is called the MILO-VCO. In this device, the MILO and VCO are operated synchronously and generate high-power microwaves. The MILO-VCO is investigated in detail with particle-in-cell (PIC) methods (KARAT code). In simulation, the diode voltage is 640 kV and the current is 50 kA. The total peak power of the MILO-VCO is 5.22 GW and the corresponding power conversion efficiency is 16.3%. In the MILO-VCO, the peak power of the MILO is 3.91 GW and its frequency is 1.76 GHz; the peak power of the VCO is 1.33 GW and its frequency is 3.79 GHz.
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84.40.Fe Microwave tubes (e.g., klystrons, magnetrons, traveling-wave, backward-wave tubes, etc.)

Instability of relativistic electron-beam–dielectric system as a mechanism for microwave generation

Ling-Bao Kong, Chao-Hai Du, Pu-Kun Liu, and Liu Xiao

J. Appl. Phys. 102, 103305 (2007); http://dx.doi.org/10.1063/1.2817642 (3 pages) | Cited 7 times

Online Publication Date: 30 November 2007

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The dispersion relation of relativistic rectilinear electron beam propagating along a guide magnetic field in a dielectric is investigated by cold fluid model. In such a system, due to anomalous Doppler effect, the instability occurs when the electron velocity exceeds the wave phase velocity. The growth rate and spatial growth rate are studied analytically and the nonlinear saturated efficiency is given analytically for the first time. Numerical results show that the saturated efficiency approaches about 10%–30%. The distinctive interaction mechanism is promising for the design of a new kind of compact high-power microwave generation devices.
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41.75.Ht Relativistic electron and positron beams
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
41.20.Jb Electromagnetic wave propagation; radiowave propagation
84.40.-x Radiowave and microwave (including millimeter wave) technology
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