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  • 1
    Digitale Medien
    Digitale Medien
    Temporal evolution of the electron distribution function in an electron cyclotron resonant discharge (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 5306-5313 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We present time-resolved experimental measurements of the electron distribution function f(v(parallel),v⊥,t) in a pulsed, partially ionized, electron cyclotron resonance (ECR)-produced plasma. The discharge has some characteristics similar to those used in plasma processing applications. These properties include ECR production in a strong magnetic field and low electron temperature (Te〈5 eV). In addition, electron-neutral collisions play an important role. A novel analyzer is used to study the dependence of f(v(parallel),v⊥,t) on velocities both parallel and perpendicular to the magnetic field. This information cannot be obtained with a simple Langmuir probe. The temporal evolution of f(v(parallel),v⊥,t) is examined during plasma formation, with the source biased, with the source grounded and in the afterglow.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.350240
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  • 2
    Digitale Medien
    Digitale Medien
    Vibrational autoionization in H2: Vibrational branching ratios and photoelectron angular distributions near the v+=3 threshold (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 7911-7917 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Vibrational branching ratios and photoelectron angular distributions are reported for photoionization of normal (the equilibrium ortho/para mixture) hydrogen in the region just above the v+=3 ionization limit. This region contains a number of vibrationally autoionizing Rydberg states, and the goal of the work was to observe experimentally the characteristic behavior associated with the decay of these states that was predicted by Raoult and Jungen [J. Chem. Phys. 74, 3388 (1981)] on the basis of an MQDT (multichannel quantum defect theory) calculation on para-H2 (J‘=0). We have indeed observed that vibrational autoionization strongly favors the ionization channel representing the minimum change in the vibrational state of the ion core, as predicted. We also observed a sharp reduction in the photoelectron asymmetry of the v+=3 (and, to a lesser extent, the v+=2) ionization channel for resonant photoionization. Hence, qualitative agreement with theory is observed; however, a quantitative comparison now requires an extended calculation that includes the additional rotational levels that were populated under the present experimental conditions.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.463466
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  • 3
    Digitale Medien
    Digitale Medien
    Resonance effects in the 5σ−1 photoionization channel of CO (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 7433-7439 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Vibrational branching ratios and photoelectron angular distributions are reported for the 5σ−1 photoionization channel of CO in the range 16 eV〈hν〈45 eV. Striking non-Franck–Condon effects are observed in both the branching ratios and angular distributions as a result of various autoionizing states and a σ shape resonance that lie in this spectral range. The goal of the present measurement was to observe definitive evidence for the σ shape resonance via its non-Franck–Condon effects on the vibrational ionization channels. Guided by recent calculations [Smith, Lynch, and McKoy, J. Chem. Phys. 85, 6455 (1986)], we examined the broad structure in the vibrational branching ratios and angular distributions in the range 25 eV 〈hν〈40 eV. There, we found clear evidence for the σ shape resonance in the quantities β(v+=0 and 1) and σ(v+=2)/σ(v+=0). Substantial differences between theory and experiment for the σ(v+=1)/σ(v+=0) branching ratio, however, serve to define the limitations of the current single-channel picture for this process.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.462393
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  • 4
    Digitale Medien
    Digitale Medien
    Shape-resonance-enhanced continuum–continuum coupling in photoionization of CO2 (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 1556-1563 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: We have measured photoionization branching ratios and photoelectron asymmetry parameters for photoionization of CO2 leading to the first four electronic states of CO2+ over the photon energy range from 20 to 50 eV. The motivation for this work was the prediction by Lucchese [J. Chem. Phys. 92, 4203 (1990)] that the σu shape resonance in the (4σg)−1 C˜ 2Σg+ ionization channel would influence the photoionization dynamics in the other valence-shell continua through continuum–continuum channel interaction, with the main effect occurring in the (3σu)−1 B˜ 2Σu+ channel. Indeed, clear evidence for this phenomenon is observed in this channel, the most prominent indication being a broad, shallow minimum in the asymmetry parameter at ∼40 eV. Comparisons of the present results with theory and other measurements reflect good overall agreement and provide some guidance regarding the effectiveness of alternative approximations used in the theoretical calculations.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.465324
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  • 5
    Digitale Medien
    Digitale Medien
    Multichannel boxcar-averaged measurements of plasma parameters made using a digital storage scope (1988)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 59 (1988), S. 1081-1084 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: We present a technique for rapidly acquiring time-resolved, ensemble-averaged Langmuir probe characteristics. Fifty probe characteristics are acquired using a digital storage oscilloscope in the time it would take to acquire a one-probe characteristic using a single-channel boxcar averager. A single Langmuir probe is used, and the probe bias is swept quite slowly, so that the probe is always in equilibrium with the plasma. A method for the automatic extraction of electron temperature, electron density, and the plasma potential from the acquired probe characteristics is described. This technique for acquisition and analysis is applied to the study of plasma decay and the effects of rf excitation in a pulsed, strongly magnetized plasma.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1139730
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  • 6
    Digitale Medien
    Digitale Medien
    Reentrant cavity as a low-power plasma source (1986)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 57 (1986), S. 2957-2960 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: A low-power source of plasma employing ECRH microwave breakdown in a reentrant cavity is described. The cavity has the following features: its dimensions can be made much smaller than its resonant wavelength, cavity Q values of several hundred are not difficult to achieve, and the vacuum rf electric field is uniform near its center. The plasma density to power ratio is roughly 109 cm−3 per watt for powers up to about 10 W. A smooth radial profile and a temperature of 5–10 eV are observed, and the plasma is very quiescent (δn/n is less than 1%). The cavity's construction and performance is described and compared to the performance of a simple loop antenna in a nonresonant structure.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1139023
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  • 7
    Digitale Medien
    Digitale Medien
    The contribution of cyclotron heating induced spatial modulation of electron magnetization to tokamak current drive (1986)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 29 (1986), S. 247-251 
    Details
    ISSN: 1089-7666
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Application to a tokamak of electron-cyclotron resonant heating (ECRH) injected at a given poloidal angle will result in a small but important variation of average electron magnetic moment with poloidal angle. This, coupled with the dependence of magnetic field strength on poloidal angle, will result in the transmission of a net toroidal force to the electrons, the direction and magnitude of which depend on the poloidal angle at which the ECRH is injected and the direction of velocity of the electrons by which it is absorbed. The geometries for which this mechanism adds to the Fisch–Boozer mechanism [Phys. Rev. Lett. 45, 720 (1980)] are described, as are those for which this mechanism is in opposition. Taking this mechanism into account, it is demonstrated that electrons at large minor radii can be driven with significantly greater efficiency if resonance is on the inboard side of the tokamak than if it is on the outboard side, and the ratio of the two efficiencies is calculated for the case of Coulomb collisionality in the limit of large Larmor radius. The case of turbulence-dominated collisionality is considered, and a general prediction of the ratio of the efficiency of this drive mechanism to that of the Fisch–Boozer mechanism is presented, in which the ratio of the efficiencies is given in terms of the dependence of the slowing-down time on velocity. The mechanism described herein provides a significant correction to predictions of current drive efficiency for infinite Larmor radius Coulomb collisionality, and is likely to provide a more significant correction yet for more realistic models of collisionality.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.865982
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  • 8
    Digitale Medien
    Digitale Medien
    Vibrationally resolved photoelectron angular distributions and branching ratios for the carbon dioxide molecule in the wavelength region 685–795 A(ring) (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 3923-3934 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Measurements of vibrational branching ratios and photoelectron angular distributions have been made in the regions of the Tanaka-Ogawa, Lindholm, and Henning series for the CO2 molecule. The behavior of these parameters was found to be sensitive to which particular resonance is excited, with considerable intensity going into vibrational modes other than the symmetric stretch. An initial analysis of some of the data taken is presented. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.471249
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  • 9
    Digitale Medien
    Digitale Medien
    Selective population of spin–orbit levels in the autoionization of a polyatomic molecule: Branching ratios and asymmetry parameters for the Tanaka–Ogawa Rydberg series in CO2 (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 8768-8779 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The spin–orbit selectivity of angle-resolved photoelectron spectra was used to provide new information on the electronic structure, symmetry, and decay dynamics of members of the autoionizing Tanaka–Ogawa Rydberg series in CO2. This represents the first time that spin–orbit selectivity has been used to obtain such information for a polyatomic molecule. The spin–orbit photoelectron branching ratios were used to show that the angular momentum quantum number λ of the excited Rydberg electron does not change upon autoionization. Furthermore, a consideration of the present results together with previous calculations of the relative intensities of the discrete and continuum ionization channels shows that the most probable electron configuration for the Tanaka–Ogawa Rydberg series is ...(πu)3(πg)4ndδg and that autoionization proceeds primarily via a dδg→εfδu process for the totally symmetric vibronic components of the ion. The asymmetry parameter β was determined for individual spin–orbit components of the various vibronic bands of the X˜ 2Πg state and is discussed in terms of recent theoretical calculations. The Rydberg series appears to be well described by Ωcω coupling, even for relatively low principal quantum numbers. The general utility of this technique for autoionizing Rydberg states and its extension to multiphoton ionization of Rydberg states that lie below the first ionization threshold are discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.466731
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  • 10
    Digitale Medien
    Digitale Medien
    A modification of the percutaneous tracheostomy technique (2000)
    Oxford, UK : Blackwell Science Ltd
    Anaesthesia 55 (2000), S. 0 
    Details
    ISSN: 1365-2044
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Medizin
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1046/j.1365-2044.2000.01557-10.x
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