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  • Articles  (3)
  • American Institute of Physics (AIP)  (3)
  • Physics of Plasmas  (3)
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  • 1
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    American Institute of Physics (AIP)
    Publication Date: 2015-04-30
    Description: Periodic fluctuations in the frequency range from 0.3 to 3 kHz were experimentally investigated in capacitively coupled radio frequency (13.56 MHz) oxygen plasma. The Gaussian beam microwave interferometry directly provides the line integrated electron density fluctuations. A system of two Langmuir probes measured the floating potential spatially (axial, radial) and temporally resolved. Hence, the floating potential fluctuation development is mapped within the discharge volume and provides a kind of discharge breathing and no wave propagation. Finally, it was measured the optical emission pattern of atomic oxygen during the fluctuation as well as the RF phase resolved optical emission intensity at selected phase position of the fluctuation by an intensified charge-coupled device camera. The deduced excitation rate pattern reveals the RF sheath dynamics and electron heating mechanisms, which is changing between low and high electronegativity during a fluctuation cycle. A perturbation calculation was taken into account using a global model with 15 elementary collision processes in the balance equations for the charged plasma species ( O 2 + ,   e ,   O − ,   O 2 − ) and a harmonic perturbation. The calculated frequencies agree with the experimentally observed frequencies. Whereby, the electron attachment/detachment processes are important for the generation of this instability.
    Print ISSN: 1070-664X
    Electronic ISSN: 1089-7674
    Topics: Physics
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  • 2
    Publication Date: 2016-02-12
    Description: This contribution presents experimental results about the mode transition of an inductively coupled radio frequency (RF) (13.56 MHz) argon discharge at different total gas pressures. In particular, the positive ion saturation current and the line integrated electron density are measured by Langmuir probe and 160 GHz microwave interferometer, respectively. The mode transition strongly depends on the total gas pressure and can appear stepwise or continuously. The space resolved positive ion saturation current is separately shown for the E- and H-mode at different total gas pressures. Therewith, the pressure dependency of the RF sheath thickness indicates a collisional sheath. The hysteresis phenomenon during the E-H and the inverse H-E transition is discussed within the framework of the matching situation for different total gas pressures. The hysteresis width is analyzed using the absorbed power as well as the coil voltage and current. As a result, the width strongly increases with pressure regarding the power and the coil voltage in the E-mode and remains constant in the H-mode. In addition, the phase shift between the coil voltage and current shows a hysteresis effect, too.
    Print ISSN: 1070-664X
    Electronic ISSN: 1089-7674
    Topics: Physics
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  • 3
    Publication Date: 2015-11-12
    Description: Plasma medicine utilizes the combined interaction of plasma produced reactive components. These are reactive atoms, molecules, ions, metastable species, and radiation. Here, ultraviolet (UV, 100–400 nm) and, in particular, vacuum ultraviolet (VUV, 10–200 nm) radiation generated by an atmospheric pressure argon plasma jet were investigated regarding plasma emission, absorption in a humidified atmosphere and in solutions relevant for plasma medicine. The energy absorption was obtained for simple solutions like distilled water (dH 2 O) or ultrapure water and sodium chloride (NaCl) solution as well as for more complex ones, for example, Rosewell Park Memorial Institute (RPMI 1640) cell culture media. As moderate stable reactive oxygen species, hydrogen peroxide (H 2 O 2 ) was studied. Highly reactive oxygen radicals, namely, superoxide anion (O 2 •− ) and hydroxyl radicals ( • OH), were investigated by the use of electron paramagnetic resonance spectroscopy. All species amounts were detected for three different treatment cases: Plasma jet generated VUV and UV radiation, plasma jet generated UV radiation without VUV part, and complete plasma jet including all reactive components additionally to VUV and UV radiation. It was found that a considerable amount of radicals are generated by the plasma generated photoemission. From the experiments, estimation on the low hazard potential of plasma generated VUV radiation is discussed.
    Print ISSN: 1070-664X
    Electronic ISSN: 1089-7674
    Topics: Physics
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