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  • 1
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Fully noninductive, steady-state electron cyclotron current drive (ECCD) has been demonstrated for the first time in experiments carried out in the tokamak à configuration variable (TCV) [O. Sauter et al., Phys. Rev. Lett. 84, 3322 (2000)]. By appropriately distributing six 0.45 MW ECCD sources over the discharge cross section, fully noninductive, stable, and stationary plasmas with Ip up to 210 kA were obtained for the full discharge duration of 1.9 s, corresponding to more than 900 energy confinement times and more than 10 current redistribution times at an average current drive efficiency η20CD=0.01[1020 A W−1 m−2]. These experiments have also demonstrated for the first time the steady recharging of the ohmic transformer using ECCD only. The effect of localized off-axis electron cyclotron heating (ECH) and EC current drive (ECCD) (co- and counter-) is investigated showing that locally driven currents amounting to only 1% of Ip significantly alter sawtooth periods and crash amplitudes. An improved quasi-stationary core confinement regime, with little or no sawtooth activity, has been obtained by a combination of off-axis ECH and on-axis CNTR–ECCD. © 2001 American Institute of Physics.
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 2421-2430 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electron beam instabilities occurring in a gyrotron electron beam can induce an energy spread which might significantly deteriorate the gyrotron efficiency. Three types of instabilities are considered to explain the important discrepancy found between the theoretical and experimental efficiency in the case of quasi-optical gyrotrons (QOG): the electron cyclotron maser instability (ECMI), the electrostatic Bernstein instability (BI) and the Langmuir instability (LI). When the magnetic field gradient in drift tubes of QOG is low, the ECMI can develop in the drift tube at very low electron beam currents. Experimental measurements show that with a proper choice of absorbing structures in the beam tunnel, this instability can be suppressed. At high beam currents, the BI can induce a significant energy spread at the entrance of the interaction region. The induced energy spread scales approximately linearly with the electron beam density and for QOG one observes that the beam density is significantly higher than the beam density of an equivalent cylindrical cavity gyrotron. © 1998 American Institute of Physics.
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3043-3048 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Extensive simulations are performed to investigate effects of electron cyclotron instabilities on the gyrotron beam quality, using two-dimensional axisymmetric particle-in-cell (PIC) codes. Both electrostatic and electromagnetic models, as well as realistic geometries of the gyrotron, are considered. It is found that a large beam density can lead to an electrostatic-instability-induced energy spread which substantially degrades the gyrotron efficiency. © 1997 American Institute of Physics.
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  • 4
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The parallel velocity distribution function of the weakly relativistic electron beam of a quasi-optical gyrotron has been determined by measuring the Doppler-shifted Electron Cyclotron Emission (ECE) at an angle θ=15° with respect to the external magnetic dc-field. Due to the Doppler shift, the frequency of the spontaneous cyclotron emission at the fundamental (ν0=100 GHz) is upshifted to 140 GHz. A broadening of the spectrum up to 10 GHz [full width at half maximium (FWHM)] was measured. The measured mean frequency agrees well with the theoretical predictions, but the observed line-width, and hence the parallel velocity distribution function, is 2–3 times larger than expected. Considerations on ECE-measurements of the electron beam energy spread, performed at larger angles θ, are also discussed. © 1996 American Institute of Physics.
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 70 (1999), S. 2703-2707 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A silicon-based temperature stabilized axial Hall probe with an absolute accuracy of ±40 ppm in the full range between 0 and 6 T is presented. The absolute calibration of the probe is performed against a nuclear magnetic resonance (NMR) probe. The application of the probe to a magnetic field profile of a 5 T superconducting magnet system, with field gradients as high as 30 T/m, reaching an overall accuracy of better than ±100 ppm, is demonstrated. In addition to the high absolute accuracy, this Hall probe allows high spatial resolution measurements of inhomogeneous fields in configurations where present NMR probes are not usable. © 1999 American Institute of Physics.
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  • 6
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A quasi-optical gyrotron (QOG) designed for operation at the fundamental ( fce(approximately-equal-to)100 GHz) exhibits simultaneous emission at fce and 2fce (second harmonic). For a beam current of 4 A, 20% of the total rf power is emitted at the second harmonic. The experimental measurements show that the excitation of the second harmonic is only possible when the fundamental is present. The frequency of the second harmonic is locked by the frequency of the fundamental. Experimental evidence shows that when the second harmonic is not excited, total efficiency is enhanced.
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  • 7
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 651 (1992), S. 0 
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 239-244 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Intramolecular vibrational energy redistribution and fragmentation dynamics in I2(B,v=22) (centered ellipsis) Nen (n=2–6) and I2(B,v=21) (centered ellipsis) Nen (n=2–5) clusters is studied by hybrid quantum/classical techniques and the results are compared with experiments. A vibrational version of the molecular dynamics with quantum transitions (MDQT) treatment is used in which the vibrational degree of freedom of I2 is treated quantum mechanically while all the other degrees of freedom are treated classically. The potential energy surface is represented as a sum of pairwise interactions with parameters taken from the literature. The calculated product state distributions are in very good agreement with the experiments. Fragmentation lifetimes were also calculated and agree reasonably well with those measured in time-dependent experiments. Fragmentation proceeds via sequential ejection of Ne monomers through three different mechanisms: (i) sequential intramolecular vibrational redistribution plus vibrational predissociation (in which the I2 molecule loses more than one quantum of vibration); (ii) direct vibrational predissociation (in which the I2 molecule loses only one quantum of vibration); (iii) evaporation (in which the I2 molecule remains in the same vibrational state). © 1999 American Institute of Physics.
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  • 9
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 1027-1034 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The A˜ continuum photoexcitation of ICN in an Ar matrix is studied using an implementation of the molecular dynamics with quantum transitions method of Tully. Five excited electronic potential energy surfaces of the ICN molecule, 3Π0+, 1Π1(A′,A″), 3Π1(A′,A″), as well as its ground state, are included in these calculations. The couplings between electronic states at large I–CN internuclear distances are modeled using a diatomic in molecules treatment of the mixing of the different spin-orbit states of iodine induced by the Ar atoms. The electronic motion, as well as the I–CN distance and the corresponding bending angle, are treated quantum mechanically using wave-packet techniques. The rotation and translation of the ICN molecule in the Ar cage are treated classically, as well as the motion of the Ar atoms. In contrast with previous calculations, in which all nuclear degrees of freedom were treated classically, we found a 2% of CN cage exit during the first 0.5 ps of the dynamics. © 2000 American Institute of Physics.
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  • 10
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 2844-2850 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Photodissociation of ICN in an Ar matrix is studied by molecular dynamics with quantum transitions (MDQT) with the motion of the nuclei treated classically and the electronic motion quantum mechanically. Four electronic surfaces and their corresponding couplings are included in the calculations. The coupling between electronic states at large I-CN internuclear distances is modeled using a diatomic in molecules (DIM) treatment of the mixing of the different spin-orbit states of iodine induced by the Ar atoms. For a total propagation time of 3 ps, no cage exit is found and 44% of the trajectories recombine to the ground electronic state. The principal mechanism for geminate recombination involves the reaction path 3Π0+→1Π1→1Σ0++. © 1998 American Institute of Physics.
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