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  • 1
    Electronic Resource
    Electronic Resource
    Plasma effect on shock waves in a supersonic flow (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 3258-3264 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An experimental study of the plasma effect on the structure of an attached conical shock front appearing at the front end of a cone-shaped model has been carried out in a Mach 2.5 stream. The tip and the body of the model are designed as the cathode and anode, which are separated by a conical-shaped ceramic insulator providing a 5 mm gap for gaseous discharge. The electric field intensity near the cathode is enhanced by the sharpness of the tip. The experimental results show that the diffused discharge can produce plasma distributed symmetrically around the tip in the region in front of the shock wave. It is observed that such plasma can cause shock wave moving upstream with its shock front detached from the model. The shock front is also becoming more and more diffusive and having an increasing shock angle as seen in the shadow video graphs of the flow. A physical mechanism of the observed plasma effect on this type of shock wave is also presented. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1376422
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  • 2
    Electronic Resource
    Electronic Resource
    Temperature measurement of an atmospheric-pressure plasma torch (1999)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 70 (1999), S. 3032-3034 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A simple method to make a temperature measurement in an atmospheric-pressure plasma torch with a density of 1013 electrons/cm3 is developed. The method is based on thermal equilibrium and a detailed analysis of heat loss from a copper wire placed in a torch. The wire diameter, which regulates heat loss, is systematically reduced to increase the temperature of the wire segment in the torch. This process yields a critical wire diameter: Smaller diameters melt and larger diameters are not affected. For the critical diameter the wire temperature in the torch is approximated as the wire melting temperature. This temperature and an analysis of heat input from the torch and heat loss from the wire combine to provide a temperature measurement in the 1300–2200 K range. Using this technique, the temperature of a plasma torch was determined to be approximately 1760 K. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149864
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  • 3
    Electronic Resource
    Electronic Resource
    Generation of density irregularities and whistler waves by powerful radio waves in the polar ionosphere (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 277-284 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: It is shown that a powerful high-frequency (HF) wave can excite a thermal instability in the E region of the polar ionosphere to introduce a significant electron temperature perturbation. This instability has a broad spatial spectrum with an upper bound. The temperature perturbation then develops nonlinearly, via the electron thermal diffusion process, into spatially periodic irregularities along the geomagnetic field, where the spatial period of the irregularities in the range between 460 m and 1.3 km is mainly governed by the minimum wavelength in the spectrum of the instability. Due to the decreasing dependence on the electron temperature of the recombination rates of electrons with the E region dominant ion species NO+ and O2+, the background plasma density as well as the electrojet current are also perturbed spatially in a similar fashion as the electron temperature irregularities. If an amplitude-modulated HF wave with a modulation frequency in the frequency range between 2 and 30 kHz is used to modulate the electrojet current in time, the density irregularities can effectively convert the current perturbation into a spatially distributed mode current of whistler waves. This direct excitation process enhances the generation efficiency of whistler waves and reduces their harmonic components. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1334610
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  • 4
    Electronic Resource
    Electronic Resource
    Observation of shock wave elimination by a plasma in a Mach-2.5 flow (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 1345-1348 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An experimental study on the influence of a plasma on the structure of an attached conical shock front appearing at the front end of a missile-shaped model has been carried out in a Mach-2.5 flow. The tip and the body of the model are designed as the cathode and anode for gaseous discharge, which produces a spraylike plasma moving around the tip. It is observed that the plasma has caused the shock front to separate from the model. The shock wave moves upstream in the form of a detached bow shock a sensible distance away from the model tip. The detached shock front appears to be highly dispersed in its new location as seen in the shadow video graphs of the flow. As the discharge current increases, experimental evidence shown in the video further reveals a distinct state of the flow without the presence of any shock wave. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873776
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  • 5
    Electronic Resource
    Electronic Resource
    Monte Carlo simulation of electron behavior in an electron cyclotron resonance discharge (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 4197-4204 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electron behavior in an electron cyclotron resonance microwave discharge maintained by the TM01 mode fields of a cylindrical waveguide has been investigated via a Monte Carlo simulation. Since this discharge has high degree of ionization (≥1%), a self-consistent simulation of the plasma dynamics is achieved through the use of the ponderomotive and grad B (−μ∇(parallel)B) forces. Accumulation of negative charges on the boundary surface sets up a sheath whose influence is also taken into account. The time averaged, spatially dependent electron energy distribution (EED) is computed self-consistently by integrating electron trajectories subjected to the microwave fields, the divergent background magnetic field, the space charge field, and the sheath field, and taking into account electron–electron collisions and collisions with the neutral hydrogen atoms. The EED is characterized by two electron temperatures with the population of the tail increasing for decreasing pressure. At low pressures (∼0.5 mTorr), the sheath potential is on the order of 100 V and decreases with increasing pressure. This observation suggests a pressure range for operation of reactors for diamondlike carbon film deposition.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352824
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  • 6
    Electronic Resource
    Electronic Resource
    Frequency up-conversion of a high-power microwave pulse propagating in a self-generated plasma (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 5376-5380 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In the study of the propagation of a high-power microwave pulse, one of the main concerns is how to minimize the energy loss of the pulse before reaching the destination. In the very high-power region, one has to prevent the cutoff reflection caused by the excessive ionization in the background air. A frequency autoconversion process that can lead to reflectionless propagation of powerful electromagnetic pulses in self-generated plasmas is studied. The theory shows that under the proper condition the carrier frequency ω of the pulse shifts upward during the growth of local plasma frequency ωpe. Thus, the self-generated plasma remains underdense to the pulse. A chamber experiment to demonstrate the frequency autoconversion during the pulse propagation through the self-generated plasma is conducted. The detected frequency shift is compared with the theoretical result calculated by using the measured electron density distribution along the propagation path of the pulse. Good agreement is obtained.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.350557
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  • 7
    Electronic Resource
    Electronic Resource
    Propagation of high-power microwave pulses in air breakdown environment (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 2762-2766 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A chamber experiment is conducted to study the propagation of high-power microwave pulses through the air. Two mechanisms responsible for two different degrees of tail erosion have been identified experimentally. The optimum pulse amplitude for maximum energy transfer through the air has also been determined.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345442
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  • 8
    Electronic Resource
    Electronic Resource
    Filamentation instability of upper hybrid wave in magnetoplasmas (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 4697-4702 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A four-wave parametric coupling leading to the filamentation of a large amplitude upper hybrid wave and the generation of magnetic field-aligned density striation in collisional magnetoplasmas is studied. The dispersion relation is derived including the nonlinear effects of ponderomotive force, thermal pressure force, and beating currents. It is analyzed to obtain the threshold field and the growth rate which are applied to the high latitude ionospheric modifications by powerful high frequency waves. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872036
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  • 9
    Electronic Resource
    Electronic Resource
    The role of nonlinear beating currents on parametric instabilities in magnetoplasmas (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 3957-3965 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A general coupled mode equation for the low-frequency decay modes of parametric instabilities in magnetoplasmas is derived. The relative importance of the nonlinear contributions from the ponderomotive force, nonlinear beating current, and anisotropic effect to the parametric coupling is then manifested by the coupling terms of the equation. It is first shown in the unmagnetized case, that the contribution of the nonlinear beating current is negligibly small because of the small coefficient (i.e., weight) of this current contribution, instead of the beating current itself. It then follows that the weight of the beating current contribution increases significantly in the magnetized case, and consequently, this contribution to the parametric coupling is found to be important, as exemplified by two specific examples. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871568
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  • 10
    Electronic Resource
    Electronic Resource
    Cascading of the upper hybrid/electron Bernstein wave in ionospheric heating experiments (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 3044-3052 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Parametric decay of an upper hybrid/electron Bernstein pump wave into an upper hybrid/electron Bernstein sideband wave and a lower hybrid decay wave in the long-wavelength regime is studied. It is found that the process associated with the electron Bernstein pump wave has a lower threshold field than that of a similar decay process of the upper hybrid pump wave when the instability is excited in the region away from the double resonance layer. Near the double resonance layer, where the upper hybrid resonance frequency equals a harmonic of the electron cyclotron frequency, the upper hybrid wave and the electron Bernstein wave become linearly coupled, and the threshold field of the parametric decay process changes back to a similar functional dependence as that of the upper hybrid decay process. Thus, their threshold fields approach each other. When incorporated with appropriate nonlinear scattering processes, this instability process along with its cascading is proposed to be the generation mechanism for the downshifted maximum (DM), 2DM, 3DM, ... etc. features as well as the upshifted maximum (UM) feature in the stimulated electromagnetic emission spectrum observed in ionospheric heating experiments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870929
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