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  • American Institute of Physics (AIP)  (15)
  • 2000-2004  (11)
  • 1985-1989  (4)
  • 2001  (11)
  • 1989  (4)
  • 1
    Digitale Medien
    Digitale Medien
    Pedestal profiles and fluctuations in C-Mod enhanced D-alpha H-modes : The 42nd annual meeting of the division of plasma physics of the American Physical Society and the 10th international congress on plasma physics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 2033-2040 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: High resolution measurements on the Alcator C-Mod tokamak [I. H. Hutchinson et al., Phys. Plasmas 1, 1551 (1994)] of the transport barrier in the "Enhanced Dα" (EDA) regime, which has increased particle transport without large edge localized modes, show steep density and temperature gradients over a region of 2–5 mm, with peak pressure gradients up to 12 MPa/m. Evolution of the pedestal at the L-H transition is consistent with a large, rapid drop in thermal conductivity across the barrier. A quasi-coherent fluctuation in density, potential, and Bpol, with f0∼50–150 kHz and kθ∼4 cm−1, always appears in the barrier during EDA, and drives a large particle flux. Conditions to access the steady-state EDA regime in deuterium include δ〉0.35, q95〉3.5, and L-mode target density n¯e〉1.2×1020 m−3. A reduced q95 limit is found for hydrogen discharges. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1348329
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  • 2
    Digitale Medien
    Digitale Medien
    Particle transport in the scrape-off layer and its relationship to discharge density limit in Alcator C-Mod : The 42nd annual meeting of the division of plasma physics of the American Physical Society and the 10th international congress on plasma physics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 2107-2117 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Cross-field particle transport in the scrape-off layer (SOL) of Alcator C-Mod [Phys. Plasmas 1, 1511 (1994)] can be characterized by an effective particle diffusivity (Deff) that increases markedly with distance from the separatrix. As a consequence, recycling onto the main-chamber walls is large compared to plasma flows into the divertor volume. The SOL exhibits a two-layer structure: Steep gradients and moderate fluctuation levels are typically found in a ∼5 mm region near the separatrix (near SOL) where parallel electron conduction typically dominates energy losses. Small gradients and larger fluctuation levels with longer correlation times are found outside this region (far SOL). Deff in the near SOL increases strongly with local plasma collisionality normalized to the magnetic connection length. As the discharge density limit is approached, Deff and associated fluctuation levels become large across the entire SOL and cross-field heat convection everywhere exceeds parallel conduction losses, impacting the power balance of the discharge. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1352596
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  • 3
    Digitale Medien
    Digitale Medien
    Magnetization reversal in the pinned layer of PtMnCr/NiFe exchange biased bilayers (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 6591-6593 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A study has been made on the effect of annealing time on magnetization reversal of the pinned layer in NiFe(100 Å)/PtMnCr(500 Å) bilayers. In the as-deposited state, the PtMnCr layer is in a metastable, nonmagnetic, disordered fcc phase. Heating progressively transforms the alloy to the stable fct phase which is antiferromagnetic, providing the pinning layer for the soft ferromagnetic NiFe layer. The samples were annealed in a magnetic field at 250 °C for 1, 1.5, 2, and 8 h. The effect of annealing is to both increase the shift of the loops along the field axis and the coercivity of the pinned ferromagnetic layer. Although the widening of the loop is correlated with the degree of antiferromagnet transformation, the exact mechanism for the increased coercivity is unclear. Measurements of loops made at different field sweep rates and after different waiting times at saturation, on the sample annealed for 1.5 h, indicate two possible mechanisms for the increased coercivity: (i) thermally activated reversal of some of the antiferromagnetic layer (AFM) during the measurement of the hysteresis loop and/or (ii) spin-flop coupling between the AFM and ferromagnet moments at a partially compensated interface. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1359793
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  • 4
    Digitale Medien
    Digitale Medien
    Investigation of the rise time and damping of spin excitations in Ni81Fe19 thin films (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 6692-6694 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The rise and damping of spin excitations in three Ni81Fe19 films of thickness 50, 500, and 5000 Å have been studied with an optical pump–probe technique in which the sample is pumped with an optically triggered magnetic field pulse. The motion of the magnetization was described by the uniform mode solution of the Landau–Lifshitz–Gilbert equation. The rise time of the pulsed field within the film was smallest in the 50 Å sample and was generally greater when the pulsed field was perpendicular to the film plane. The damping constant was smallest in the 500 Å sample. The variations in the rise time and damping are attributed to the presence of eddy currents and structural disorder in the films. Under certain excitation conditions a second mode was observed in the 5000 Å sample which we believe to be a magnetostatic surface mode. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1357142
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  • 5
    Digitale Medien
    Digitale Medien
    Thermal activation of magnetization reversal in spin-valve systems (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 5585-5591 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Magnetization reversal in the pinned layer of exchange biased spin valves is a complex process due to the exchange interaction between the ferromagnetic layer and the antiferromagnetic layer. This interaction results in progressive reversal of the antiferromagnetic layer as the magnetization of the ferromagnetic layer changes direction. This reversal of the antiferromagnet will effect the subsequent reversal of the ferromagnet. It is known that this process is thermally activated but time dependence measurements are difficult to interpret, as the exchange field is nonconstant at many positions along the hysteresis curve. Measurements have been made of the time dependence of the reversal of the antiferromagnetic layer by measuring the recoil loops, following different times spent with the ferromagnetic layer saturated in the negative direction. In this manner, the exchange field can be assumed to be constant during the reversal of the antiferromagnet. These measurements show a shift of the loop of the pinned layer towards positive fields. This shift in the loop is interpreted as being the result of reordering of the antiferromagnet. Increasing the temperature during the time spent at saturation shows that the process is driven by thermal activation. Close examination of the degree of loop shift with time spent at saturation shows behavior consistent with thermal activation governed by a distribution of activation energies. At longer times and elevated temperatures, the behavior of the antiferromagnet reversal suggests that this distribution is complex and may be multimodal. The reversal process is, however, reversible even at high temperatures indicating that the elevated temperatures do not significantly change the structure of the ferromagnetic–antiferromagnetic layers or the interface between them. Finally, measurements at 77 K show that the active portion of the energy barrier distribution will change significantly at low temperatures. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1365428
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  • 6
    Digitale Medien
    Digitale Medien
    High-resolution edge Thomson scattering measurements on the Alcator C-Mod tokamak : Papers from the thirteenth topical conference on high temperature plasma diagnostics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 1107-1110 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: A high-resolution Thomson scattering diagnostic is in operation on the Alcator C-Mod tokamak, measuring radial profiles of electron temperature and density at the plasma edge. Photons are scattered from a Nd–yttrium–aluminum–garnet laser beam pulsed at 30 Hz (1.3 J, 8 ns pulse), and are measured by a filter polychromator with four spectral channels. The polychromator measures Te in the range of 15–800 eV and ne of 0.3–3×1020 m−3. Twenty scattering volumes are located about the last closed flux surface, spaced for a nominal resolution of 1.3 mm in midplane radial coordinates. High resolution is essential for measuring edge Te and ne profiles on C-Mod, since these quantities exhibit gradient scale lengths as small as 2 mm in H mode. The steep profiles at the H mode edge are fit to a parameterized pedestal function for ease of analysis. Measured profiles are compared with edge profiles from electron cyclotron emission and visible continuum diagnostics. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1319367
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  • 7
    Digitale Medien
    Digitale Medien
    Time and temperature dependence of instability mechanisms in amorphous silicon thin-film transistors (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 54 (1989), S. 1323-1325 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We have measured the time and temperature dependence of the two prominent instability mechanisms in amorphous silicon thin-film transistors, namely, the creation of metastable states in the a-Si:H and the charge trapping in the silicon nitride gate insulator. The state creation process shows a power law time dependence and is thermally activated. The charge trapping process shows a logarithmic time dependence and has a very small temperature dependence. The results for the state creation process are consistent with a model of Si dangling bond formation in the bulk a-Si:H due to weak SiSi bond breaking stabilized by diffusive hydrogen motion. The logarithmic time dependence and weak temperature dependence for the charge trapping in the nitride suggest that the charge injection from the a-Si:H to the nitride is the rate limiting step and not subsequent conduction in the nitride.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.100704
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  • 8
    Digitale Medien
    Digitale Medien
    Synchrotron radiation Bragg angle contour mapping of crack nucleation at grain boundaries (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 65 (1989), S. 2282-2288 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: In technical materials a critical step leading to complete macroscopic failure is not the nucleation of cracks in isolated grains, but instead the transmission of rupture from grain to grain until the entire cross section is traversed. It is difficult, in general, to employ the usual microscopic observations which could provide the keys to a comprehensive mechanistic understanding of this problem. It is shown herein that monochromatic synchrotron radiation can be used to provide Bragg angular contour maps in a rapid and precise manner. These maps enable one to quantify the local strain field tensor associated with crack nucleation and propagation through a grain boundary. Based on this analysis it is then a straightforward process to determine the other mathematical properties usually associated with second rank tensors which lead to assessment of critical parameters for crack transmission at the boundary. The application of this analytical technique is experimentally demonstrated by studies of crack formation at grain boundaries in zinc bicrystals.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.343416
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  • 9
    Digitale Medien
    Digitale Medien
    Dual dielectric silicon metal-oxide-semiconductor field-effect transistors as radiation sensors (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 65 (1989), S. 1972-1976 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A new design for radiation-sensing field-effect transistors (RADFETs) is presented, involving the use of very thick silicon nitride layers deposited on top of a high-quality thermal silicon dioxide. In contrast to previous RADFET fabrication procedures, no attempt was made to introduce hole traps into the thermal oxide. Instead the trapping layer at the nitride oxide interface was used to store the positive charge which forms the basis for operation of the RADFET. Data is presented which shows hole transport in the thermal oxide. Models explaining the field dependence of the response and the saturation behavior of the dual dielectric device are given. These RADFETs are more stable than any previously described in the literature and have a sensitivity of 86 μV/rad dose at room temperature.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.342887
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  • 10
    Digitale Medien
    Digitale Medien
    High resolution visible continuum imaging diagnostic on the Alcator C-Mod tokamak : Papers from the thirteenth topical conference on high temperature plasma diagnostics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 940-943 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: A high spatial resolution CCD based one-dimensional imaging system to measure visible continuum emissivity profiles from Alcator C-Mod tokamak plasmas is described. The instrument has chordal resolution that is better than 1 mm for the edge region of the plasma, where very sharp (1 to 10 mm) gradient lengths in plasma parameters are observed after the formation of the H-mode transport barrier. Each image has up to 2048 pixels, and total spatial coverage goes from 2 cm inside of the magnetic axis to ∼4 cm outside of the last closed flux surface in the ∼22 cm horizontal minor radius plasmas. Time resolution can be varied from 0.21 ms to 4 ms; good signal to noise is achieved with 1 ms integration under typical plasma conditions. The emission over most of the plasma volume is dominated by free–free bremsstrahlung, and can be used to infer local values of the average ion charge (Zeff). Toroidally localized puffing of deuterium, nitrogen, and helium reveals that a significant contribution to the signal in the scrape-off layer at the extreme edge of the plasma can come from diatomic molecular band pseudocontinuum emission. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1323245
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