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  • 1
    Electronic Resource
    Electronic Resource
    Production of carbon clusters by laser ablation of polymers in vacuum (2002)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 91 (2002), S. 2449-2454 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Time-of-flight mass spectrometry was used for analyzing ionic species produced by Nd:YAG laser ablation of polymers [polypropylene (PP), polyethylene (PE), and polytetrafluoroethylene] in vacuum. The temporal variation of the mass distribution after the laser irradiation was investigated. The target polymers were decomposed to almost atomic species by the laser irradiation. After the laser irradiation, significant temporal evolution of carbon cluster ions (CnHm+, CnHm−, and CnFm−) was observed. This result indicates that the cluster ions are produced from atomic species via gas-phase reactions in the ablation plume with no ambient gases. The mass spectra of Cn− and CnHm− obtained from the PP and PE targets suggest that even carbon clusters (C2k) are hydrogenated more efficiently than odd ones (C2k+1) to produce C2kHm. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1434548
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  • 2
    Electronic Resource
    Electronic Resource
    Temporal behavior of the electron density profile during limiter biasing in the HYBTOK-II tokamak (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 1089-1091 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A rapid change in the detailed edge electron density profile during positively biased limiter experiment is obtained with high temporal resolution of ∼20 μs using a laser blowoff lithium beam probe technique in HYBTOK-II tokamak [IEEE Trans. Plasma Sci. PS-19, 885 (1991)]. The transient change in the electron density profile and the movement of the position where a steep density gradient is formed are experimentally observed. The temporal behavior of the electron density profile correlates well with reductions in the biasing current and Hα emission in the scrape-off layer, and the suppression of electrostatic fluctuations near the edge of the core region.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870788
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  • 3
    Electronic Resource
    Electronic Resource
    Surface production of CF, CF2, and C2 radicals in high-density CF4/H2 plasmas (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 5585-5591 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Surface production of CF, CF2, and C2 radicals in high-density CF4/H2 plasmas was examined using laser-induced fluorescence spectroscopy. No significant amount of surface production was observed in pure CF4 plasmas. The addition of H2 into CF4 plasmas enhanced the surface production of CFx and C2 from fluorocarbon film deposited on the chamber wall. The characteristics of the surface production in cw discharges are reported, in comparison with surface production in pulsed discharges. In addition, it has been found that the surface production rates are determined not by the partial pressure but by the flow rate of H2, suggesting the significant consumption of feedstock H2 in discharges. The surface production of CFx and C2 indicates that these radicals are not the precursors for the deposition of fluorocarbon film in the CF4/H2 plasma. The deposition mechanism of fluorocarbon film in the CF4/H2 plasma is discussed, taking into account the surface production of CFx and C2. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1319974
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  • 4
    Electronic Resource
    Electronic Resource
    Distributions of C2 and C3 radical densities in laser-ablation carbon plumes measured by laser-induced fluorescence imaging spectroscopy (2002)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 91 (2002), S. 4033-4039 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We measured temporal variations of the distributions of C2 and C3 radical densities in carbon plumes produced by laser ablation of graphite in ambient He gas. Laser-induced fluorescence imaging spectroscopy was used for the measurement. The temporal variations of total numbers of C2 and C3 contained in plumes were evaluated by integrating the density distributions. The experimental observations have shown that the gas-phase production of C2 is comparable to the direct production from the target, while C3 is mainly produced in gas phase by three-body reactions between C and C2. In addition, we have discussed a scenario for the temporal evolution of heavy clusters (Cn with n≥4). The present results are useful for understanding initial formation processes of carbon clusters in laser-ablation plumes. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1455151
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  • 5
    Electronic Resource
    Electronic Resource
    Characteristics of C3 radicals in high-density C4F8 plasmas studied by laser-induced fluorescence spectroscopy (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 6201-6206 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Spatial and temporal variations of C3 density in high-density octafluorocyclobutane (c-C4F8) plasmas were examined using laser-induced fluorescence spectroscopy. The C3 density varied slowly for a long time after the initiation of discharge, suggesting the importance of surface chemistry for the formation of C3. Hollow-shaped spatial distributions (the C3 density adjacent to the chamber wall was higher than that in the plasma column) were observed in the C3 density. This result indicates that C3 radicals are produced from fluorocarbon film on the chamber wall and are lost in the plasma column due to electron impact processes. The surface production of C3 was also observed in the afterglow for 1 ms after the termination of rf power. The decay time constant of the C3 density in the late (〉1 ms) afterglow, where the surface production of C3 stopped, was almost independent of discharge parameters, suggesting that the loss of C3 due to gas-phase reactions is negligible. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1321029
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  • 6
    Electronic Resource
    Electronic Resource
    Laser blow-off lithium beam probing with high temporal resolution for edge plasma diagnostics (1993)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 64 (1993), S. 2277-2284 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Laser blow-off neutral lithium beam probing with high temporal resolution has been developed to measure edge electron density profiles in a plasma. A new electron density reconstruction method, taking account of the transport of a laser blow-off beam in the plasma, improves the accuracy of the density measurement. The use of a camera system with a gate function makes it possible for us to measure the density profile with a high temporal resolution of 10–50 μs. The optimum condition for shutter timing and period to observe the Li i emission profile is discussed from the viewpoints of the beam penetration into the plasma and the accuracy of measurement. A rapid temporal evolution of the edge electron density profile during limiter biasing in a small tokamak HYBTOK-II was successfully obtained by this system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143923
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  • 7
    Electronic Resource
    Electronic Resource
    Edge plasma density reconstruction for fast monoenergetic lithium beam probing (1993)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 64 (1993), S. 1699-1704 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Two different electron density reconstruction methods for 8-keV neutral lithium beam probing have been developed for the Compact Helical System (CHS). Density dependences on emission and ionization processes are included by using effective rate coefficients obtained from the collisional radiative model. Since the two methods differ in the way the local beam density in the plasma is determined, the methods have different applicable electron densities. The beam attenuation is calculated by iteration from the electron density profile in method I. In method II, the beam remainder at the observation point z is determined by integrating the Li i emission intensity from z toward the position of emission tail-off. At the emission tail-off, the fast lithium beam is completely attenuated. Selecting an appropriate method enables us to obtain edge electron density profile well inside the last closed flux surface for various ranges of plasma densities (1012–5×1013 cm−3). The electron density profiles reconstructed by these two different methods are in good agreement with each other and are consistent with results from ruby laser Thomson scattering.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143996
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  • 8
    Electronic Resource
    Electronic Resource
    Measurements of negative ion density in high-density oxygen plasmas by probe-assisted laser photodetachment (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 697-702 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Probe-assisted laser photodetachment has been developed and applied to measure the negative ion density (n−) in high-density plasmas. Temporal variation of n− is obtained in high-density and low-pressure oxygen plasmas generated by helicon wave excitation. Negative ions are not observed in the active discharge phase and rapid increase of n− is seen only in the afterglow phase. This efficient production of negative ions is considered to be due to dissociative electron attachment to metastable molecular states, O2M(A3Σu+, A′3Δu, and c1Σu−), located at 4–5 eV above the ground state. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.366740
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  • 9
    Electronic Resource
    Electronic Resource
    Kinetics of fluorine atoms in high-density carbon–tetrafluoride plasmas (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 82 (1997), S. 5938-5943 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Reaction processes of fluorine (F) atoms in high-density carbon–tetrafluoride (CF4) plasmas were investigated using vacuum ultraviolet absorption spectroscopy. A scaling law nF∝(nenCF4)0.5–0.7 was found experimentally, where nF is the F atom density and ne and nCF4 stand for the electron and parent gas (CF4) densities, respectively. The lifetime measurement in the afterglow showed that the decay curve of the F atom density was composed of two components: a rapid decay in the initial afterglow and an exponential decrease in the late afterglow. The decay time constant in the initial afterglow τ1 satisfied the scaling law τ1∝(nenCF4)−(0.3–0.4), which is a consistent relationship with the scaling law for the F atom density. The two scaling laws and the lifetimes of CFx radicals suggest that the major loss process of F atoms in the initial afterglow is the reaction with CFx radicals (probably, x=3) on the wall surface. The loss process in the late afterglow was simple diffusion to the wall surface. The surface loss probability of F atoms on the chamber wall was evaluated from the decay time constant in the late afterglow, and was on the order of 10−3. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.366495
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  • 10
    Electronic Resource
    Electronic Resource
    Absolute density and reaction kinetics of fluorine atoms in high-density c-C4F8 plasmas (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 7482-7487 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Absolute density and reaction kinetics of fluorine (F) atoms in high-density octafluorocyclobutane (c-C4F8) plasmas were examined using vacuum ultraviolet absorption spectroscopy. The F atom densities, corresponding to electron densities ranging from 1×1011 to 5×1012 cm−3, were 1×1012–5×1013 cm−3 for gas pressures of 2–7 mTorr and rf powers of 0.2–1.5 kW. The F atom density was linearly dependent on the electron density for ne〈1.5×1012 cm−3. According to lifetime measurements in the afterglow, two decay processes were found in the F atom density: exponential (first-order kinetics) and linear (zero-order kinetics) decay components. The linear-decay component became significant at high gas pressures. The time constant of the exponential-decay component ranged from 5 to 100 ms, which corresponds to surface loss probabilities of 10−1–10−3. The surface loss probability varied inversely with the F atom density. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.367511
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