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  • 1
    Electronic Resource
    Electronic Resource
    Experimental considerations concerning the velocity measurement of the relativistic electron beam in a gyrotron by means of Thomson scattering (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 2229-2236 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The feasibility of Thomson scattering to determine the beam velocity in a gyrotron has been analyzed and preliminary experiments to implement such a system on our 100 GHz quasi-optical gyrotron are reported. Although the project had to be abandoned due to technical problems, the conclusions are that for the 90° scattering arrangement discussed it should be possible to determine at least one velocity component with an acceptable signal-to-noise ratio.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.354704
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  • 2
    Electronic Resource
    Electronic Resource
    Properties of diffraction gratings used as output couplers in a quasi-optical gyrotron (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 2089-2102 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The design of a diffration grating used as an output coupler for a Fabry–Pérot resonator is presented. We then consider the problem of determining the distortion and the cross-polarization of the incident Gaussian beam. Different types of gratings and planes with straight or curvilinear grooves and elliptical, have been designed and built. The output pattern from a resonator using such a grating has been measured experimentally. We found that the elliptical grating generates the least distortion and cross-polarization. This result is attributed to the geometry of the grooves and is in excellent agreement with numerical calculations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353156
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  • 3
    Electronic Resource
    Electronic Resource
    Electron beam instabilities in gyrotron beam tunnels (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 2421-2430 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872918
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  • 4
    Electronic Resource
    Electronic Resource
    Measurement of the parallel velocity distribution function of the electron beam in a quasi-optical gyrotron by Electron Cyclotron Emission (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 3501-3506 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871500
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  • 5
    Electronic Resource
    Electronic Resource
    Operation of a quasi-optical gyrotron with a Gaussian output coupler (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 3492-3500 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The operation of a 92 GHz quasi-optical gyrotron having a resonator formed by a spherical mirror and a diffraction grating placed in −1 order Littrow mount is presented. A power of 150 kW with a Gaussian output pattern was measured. The Gaussian content in the output was 98% with less than 1% of depolarization. By optimizing the magnetic field at fixed frequency, a maximum efficiency of 15% was reached.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871499
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  • 6
    Electronic Resource
    Electronic Resource
    Study of wave–particle interaction from the linear regime to dynamical chaos in a magnetized plasmaf| (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 1452-1460 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The onset of chaotic ion dynamics in electrostatic waves is investigated in a linear magnetized plasma. The existence of a threshold for heating in agreement with the predictions of single particle Hamiltonian theories and the fast time scale for velocity space diffusion are observed in the experiment. Measurements of test-particle dynamics indicate an exponential separation of initially close ion trajectories for amplitudes above the heating threshold. Ion orbits in the different wave–particle interaction regimes are inferred using an optical tagging diagnostic method, which provides the two point correlation function in phase space.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870695
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  • 7
    Electronic Resource
    Electronic Resource
    High accuracy magnetic field measurements with a Hall probe (1999)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 70 (1999), S. 2703-2707 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149831
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  • 8
    Electronic Resource
    Electronic Resource
    Nitric Oxide-Induced Release of Acetylcholine in the Nucleus Accumbens: Role of Cyclic GMP, Glutamate, and GABA (1998)
    Oxford, UK : Blackwell Science Ltd
    Journal of neurochemistry 71 (1998), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: We have previously shown that the basal acetylcholine release in the ventral striatum is under the enhancing influence of endogenous nitric oxide (NO) and that NO donors cause pronounced increases in the acetylcholine release rate. To investigate the role of cyclic GMP, glutamate, and GABA in the NO-induced acetylcholine release, we superfused the nucleus accumbens, (Nac) of the anesthetized rat with various compounds through a push-pull cannula and determined the neurotransmitter released in the perfusate. Superfusion of the Nac with the NO donors diethylamine/NO (DEANO; 100 µmol/L), S-nitroso-N-acetylpenicillamine (SNAP; 200 µmol/L), or 3-morpholinosydnonimine (SIN-1; 200 µmol/L) enhanced the acetylcholine release rate. The guanylyl cyclase inhibitor 1H-(1,2,4)-oxodiazolo(4,3-a)quinoxalin-1-one (ODQ; 10 µmol/L) abolished the effects of DEANO and SIN-1. 6-(Phenylamino)-5,8-quinolinedione (LY-83583; 100 µmol/L), which also inhibits cyclic GMP synthesis, inhibited the releasing effects of DEANO and of SNAP, whereas the effect of SIN-1 on acetylcholine release was not influenced. The DEANO-induced release of acetylcholine was also abolished in the presence of 20 µmol/L 6,6-dinitroquinoxaline-2,3-dione (DNQX) and 10 µmol/L (±)-2-amino-5-phosphonopentanoic acid (AP-5). Simultaneous superfusion with 50 µmol/L quinpirole and 10 µmol/L 7-bromo-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine (SKF 83566) was ineffective. Superfusion with 500 µmol/L DEANO decreased the release of acetylcholine. The inhibitory effect of 500 µmol/L DEANO was reversed to an enhanced release on superfusion with 20 µmol/L bicuculline. Bicuculline also enhanced the basal release rate. These findings indicate that cyclic GMP mediates the NO-induced release of acetylcholine by enhancing the outflow of glutamate. Dopamine is not involved in this process. Only high concentrations of NO increase the output of GABA, which in turn decreases acetylcholine release. Our results suggest that cells that are able to release glutamate, such as glutamatergic neurons, are the main target of NO in the Nac.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1471-4159.1998.71010266.x
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  • 9
    Electronic Resource
    Electronic Resource
    Surface-induced miscibility gap in vapor deposited Co1−xPtx (abstract) : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 5854-5854 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have deposited (100) and (111) oriented single-crystal Co1−xPtx films (x=0.65, 0.75, and 0.86) over a range of growth temperatures from −50 to 800 °C. The Curie temperature is increased by up to 200 °C over the value expected for the homogeneous, chemically disordered alloy in the as-deposited films (of both orientations) grown near 400 °C. Measurements of the onset of magnetic ordering below the Curie temperature indicate separation into Co-rich and Pt-rich regions. High resolution x-ray measurements show no shift in the lattice constant or broadening of the x-ray peaks, and no observable strain for x=0.75, suggesting that the separated regions are small and epitaxially coherent. We interpret this as evidence for a previously unobserved miscibility gap. The bulk phase diagram shows no phase separation, but magnetic energy tends to drive the system toward immiscibility as demonstrated by the calculations of several workers. We suggest that the observed miscibility gap is an equilibrium surface effect, trapped into the bulk film by low bulk mobility. Preliminary work by Rosengren and Kundrotas supports this idea. Large perpendicular magnetic anistropy is found in those films that exhibit an anomalously high Curie temperature (films grown near 400 °C). This anisotropy is likely related to the phase separation. After annealing at high temperatures, the Curie temperature approaches the homogeneous values and the anisotropy relaxes. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362147
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  • 10
    Electronic Resource
    Electronic Resource
    Surface-induced clustering in vapor deposited Co1−xPtx and Ni1−xPtx films (abstract) : The 41st annual conference on magnetism and magnetic materials (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 5053-5053 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have depostied (100), (110), and (111) oriented single-crystal and polycrystalline Co1−xPtx (x=0.65, 0.75, 0.80) and polycrystalline Ni1−xPtx (x=0.25, 0.50) films over a range of growth temperatures from −50 to 800 °C. Previous work on CoPt3 films had demonstrated the correlation between Co clustering and perpendicular magnetic anisotropy.1 These observations motivated a model in which Co atoms cluster on the growing surface; this clustering is trapped by succeeding layers for growth temperatures below 400 °C, the lower limit of bulk atomic mobility. The (110) oriented samples show clustering and anisotropy identical to the (100) and (11) oriented samples despite the sign change of the surface segregation in the (110) orientation. The Ni–Pt alloy system is similar to Co–Pt in structure, lattice constant, and the polarizability of Pt. We have deposited Ni3Pt films; these films have significant clustering of the magnetic species which drops off rapidly after the onset of bulk mobility at 400 °C. No perpendicular magnetic anisotropy is found in these films, even though interface magnetic anisotropy values in Ni/Pt multilayers have been reported as having up to 1/4 the value of Co/Pt interfaces. Finally, in order to explore whether surface clustering is a kinetic or equilibrium effect, we have varied the deposition rate of CoPt3 over three orders of magnitude at temperatures below 400 °C. We found no dependence of clustering or anisotropy on the deposition rate, suggesting that the clustering is not kinetically limited but is a surface equilibrium effect. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.364505
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