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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 3237-3243 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The parallel electron velocity distribution function has been measured on an electron beam from a magnetron injection gun (MIG) using an E(parallel)B energy analyzer. The magnetic field, beam voltage, and beam current were scaled down from normal operating parameters. The perpendicular velocity spread, inferred under the assumption that the electrons are monoenergetic, is relatively constant for electron velocity ratios β⊥/β(parallel)(approximately-greater-than)0.7 and increases approximately linearly with the beam current. The current scaling of the perpendicular velocity spread is also consistent with electron-loss currents measured at the control anode of the MIG. Observed perpendicular velocity spreads for the gun design parameters are substantially larger than computational values.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 2 (1990), S. 640-646 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A detailed experimental study of the efficiency and output power of a pulsed gyrotron operating in the TE16,2,1 mode at 148 GHz has been conducted. A peak efficiency of 30% was achieved at 80 kV and 20 A for an output power of 480 kW. The highest output power of 925 kW, corresponding to an efficiency of 19%, was measured at 120 kV and 40 A. Two cavities with different interaction lengths (6.0λ and 4.2λ) were investigated. In both cases, agreement was found between the theoretical and experimental efficiency for beam currents up to 15–20 A. At higher currents, the experimental efficiency saturated between 20% and 25%, well below the 35%– 40% predicted by theory. No increase was obtained for modest positive or negative linear tapering of the cavity magnetic field. Measurements indicate that the beam velocity ratio decreases as beam current increases, partially explaining the reduced efficiency at higher currents. Operation in different azimuthal rotations of the cavity modes was also observed. The measured rotation was found to be consistent with the theoretical coupling between the beam and rf field.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 9 (2002), S. 3303-3310 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Cold-fluid magnetohydrodynamics equilibrium equations are solved for an infinite aspect-ratio, electron spiral torus (EST). The electrons follow approximately azimuthal orbits outside an interior ion cloud. The ion mass is assumed finite, and both electrons and ions are assumed collisionless. It is found that self-organized solutions for the electron shell and the ions exist when the EST is immersed in a neutral gas. The ion flow velocity profile is not rigid rotor. Examples of two different electron densities are examined. In each example, solutions exist for neutral gas pressure p above a critical level pc and are independent of an applied axial magnetic field. For the low-density example, the critical neutral pressure corresponds to the value observed in experiments. The equilibrium ion rotational flow velocity and self-magnetic field scale as p1/2. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A narrow linewidth (〈100 kHz), 1-kW, 137-GHz gyrotron and an efficient TE03 to TE11 cylindrical waveguide mode converter set (〉97% TE11 mode output) have been built for collective Thomson scattering diagnostics. The main goal will be to study instability driven ion density fluctuations in the Tara plug such as the drift cyclotron loss cone (DCLC), the axial loss cone (ALC), harmonics of the DCLC and ALC, and the ion two-stream instability. The heterodyne receiver and signal optics have been installed on Tara. Background electron cyclotron emission (ECE) at 139±1.5 GHz after electron cyclotron resonance heating (ECRH) in the Tara plug corresponded to equivalent blackbody temperatures of 453 and 70 eV for extraordinary and ordinary emission, respectively. The well-collimated receiver field of view completely through the Tara plug has allowed for excellent polarization discrimination of the ECE. The high-power capability of this gyrotron will allow weak fluctuation levels (ñ/n〈10−6) to be detected above this background during ECRH in the plugs.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1572-9559
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We report the experimental operation of a voltage tunable gyrotron backward wave oscillator (gyro-BWO) in the frequency range near 140 GHz. Voltage tunability is an important feature of the gyro-BWO for application as a fast tuning source for driving high power free electron lasers or cyclotron autoresonance maser amplifiers. The gyro-BWO operated in an overmoded cylindrical waveguide structure in the TE1,2 mode. The electron beam source was a Pierce-wiggler gun producing an 80 kV, 6.2 A beam. Frequency tuning with voltage between 134 and 147 GHz was achieved in the TE1,2 mode with constant magnetic field. However, this tuning was found to be discontinuous. Output powers of up to 2 kW and 2% efficiency were found, significantly below theoretical predictions for a cold beam. The theoretical beam velocity spread was modeled by a 3D beam transport code. The code results show that space charge forces, coupled with the wiggler-induced helical motion and the short cyclotron wavelength of the beam, produce large increases in velocity spread in the magnetic compression region. A beam with smaller velocity spread would be needed to make the gyro-BWO operate at the desired efficiency.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report on the design and the optical properties of a spin-coated multilayer organic microcavity. Tri(stilbene)amine blended with polysulfone as the first layer and an oxadiazole derivative (BPBD) blended with polystyrene as the second layer are sandwiched between two planar mirrors. Enhancement of the luminescence and spectrally narrow emission are observed. By means of time resolved luminescence spectroscopy we show that the spontaneous emission rate is increased in the cavity. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 59 (1988), S. 1470-1472 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A laser fluorescence diagnostic has been used for measuring the neutral hydrogen density in the central cell of the Tara thermal barrier tandem mirror. Experiments have been performed using laser-induced, resonance fluorescence detection of Hα (6563-A(ring)) radiation. Measurements were made at a number of radial positions with 1-cm resolution, from the magnetic axis to near the plasma limiter. Stray laser light contributions to the signal were eliminated with a double-pulse technique. For comparison, the chord-averaged plasma Hα radiation was analyzed under the identical conditions for which laser fluorescence data were taken.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Neutral and plasma density have been measured in the north well of the central cell of the Tara tandem mirror [Nucl. Fusion 22, 549 (1982)]. The electron plasma density and temperature on the magnetic axis were measured by Thomson scattering to be about 3×1012 cm−3 and 70 eV, respectively. The corresponding axial neutral hydrogen density was found to be 1 ×109 cm−3, while near the plasma edge at r=15 cm it reached 1×1010 cm−3. The fill gas density at r≥22.5 cm was ≈1011 cm−3. Additional information from secondary electron detectors was used to estimate the radial ion temperature distribution, which was found to have about the same width, 12 cm, as the plasma density. The resulting ion pressure profile is peaked compared to the electron pressure profile. Charge exchange losses in the well are found to have a maximum at a radius equal to half the e-folding distance of the plasma density and ion temperature distributions.
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  • 9
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The nature of a rigid, flutelike M=1 instability as seen in the Tara tandem mirror [Nucl. Fusion 22, 549 (1982); Plasma Physics and Controlled Nuclear Fusion 1984 (IAEA, Vienna, 1985), Vol. 2, p. 285] is discussed. Radial density and light emission profiles obtained by inverting chord measurements are compared to end loss radial profiles during the evolution of the mode to its nonlinear saturated state. This final state is characterized by a coherent, flutelike motion of the plasma as a whole about the machine axis.
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  • 10
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Plasma production and heating in the central cell of the Tara tandem mirror [Nucl. Fusion 22, 549 (1982); Plasma Physics and Controlled Nuclear Fusion Research, 1986, Proceedings of the 11th International Conference, Kyoto, Japan (IAEA, Vienna, 1987), Vol. 2, p. 251] have been studied. Using radio-frequency excitation by a slot antenna in the ion cyclotron frequency range (ICRF), plasmas with a peak β⊥ of 3%, density of 4×1012 cm−3, ion temperature of 800 eV, and electron temperature of 75–100 eV were routinely produced. The plasma radius decreased with increasing ICRF power, causing reduced ICRF coupling and saturation of the plasma beta. About 70% of the applied ICRF power can be accounted for in direct heating of both ions and electrons. Wave field measurements have identified the applied ICRF to be the slow, ion cyclotron wave. In operation without end plugging, the plasma parameters were limited by poor axial confinement and the requirements for maintenance of magnetohydrodynamic stability and microstability.
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