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  • 1
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    Novel linear analysis for a gyrotron oscillator based on a spectral approach (2016)
    American Institute of Physics (AIP)
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    Publikationsdatum: 2016-04-08
    Beschreibung: With the aim of gaining a better physical insight into linear regimes in gyrotrons, a new linear model was developed. This model is based on a spectral approach for solving the self-consistent system of equations describing the wave-particle interaction in the cavity of a gyrotron oscillator. Taking into account the wall-losses self-consistently and including the main system inhomogeneities in the cavity geometry and in the magnetic field, the model is appropriate to consider real system parameters. The main advantage of the spectral approach, compared with a time-dependent approach, is the possibility to describe all of the stable and unstable modes, respectively, with negative and positive growth rates. This permits to reveal the existence of a new set of eigenmodes, in addition to the usual eigenmodes issued from cold-cavity modes. The proposed model can be used for studying other instabilities such as, for instance, backward waves potentially excited in gyrotron beam tunnels.
    Print ISSN: 1070-664X
    Digitale ISSN: 1089-7674
    Thema: Physik
    Publiziert von American Institute of Physics (AIP)
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  • 2
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    Electron density and gas density measurements in a millimeter-wave discharge (2016)
    American Institute of Physics (AIP)
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    Publikationsdatum: 2016-08-10
    Beschreibung: Electron density and neutral gas density have been measured in a non-equilibrium air breakdown plasma using optical emission spectroscopy and two-dimensional laser interferometry, respectively. A plasma was created with a focused high frequency microwave beam in air. Experiments were run with 110 GHz and 124.5 GHz microwaves at powers up to 1.2 MW. Microwave pulses were 3  μ s long at 110 GHz and 2.2  μ s long at 124.5 GHz. Electron density was measured over a pressure range of 25 to 700 Torr as the input microwave power was varied. Electron density was found to be close to the critical density, where the collisional plasma frequency is equal to the microwave frequency, over the pressure range studied and to vary weakly with input power. Neutral gas density was measured over a pressure range from 150 to 750 Torr at power levels high above the threshold for initiating breakdown. The two-dimensional structure of the neutral gas density was resolved. Intense, localized heating was found to occur hundreds of nanoseconds after visible plasma formed. This heating led to neutral gas density reductions of greater than 80% where peak plasma densities occurred. Spatial structure and temporal dynamics of gas heating at atmospheric pressure were found to agree well with published numerical simulations.
    Print ISSN: 1070-664X
    Digitale ISSN: 1089-7674
    Thema: Physik
    Publiziert von American Institute of Physics (AIP)
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  • 3
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    Cryogenic testing of the 2.1 GHz five-cell superconducting RF cavity with a photonic band gap coupler cell (2016)
    American Institute of Physics (AIP)
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    Publikationsdatum: 2016-06-03
    Beschreibung: We present results from cryogenic tests of the multi-cell superconducting radio frequency (SRF) cavity with a photonic band gap (PBG) coupler cell. Achieving high average beam currents is particularly desirable for future light sources and particle colliders based on SRF energy-recovery-linacs (ERLs). Beam current in ERLs is limited by the beam break-up instability, caused by parasitic higher order modes (HOMs) interacting with the beam in accelerating cavities. A PBG cell incorporated in an accelerating cavity can reduce the negative effect of HOMs by providing a frequency selective damping mechanism, thus allowing significantly higher beam currents. The multi-cell cavity was designed and fabricated of niobium. Two cryogenic (vertical) tests were conducted. The high unloaded Q-factor was demonstrated at a temperature of 4.2 K at accelerating gradients up to 3 MV/m. The measured value of the unloaded Q-factor was 1.55 × 10 8 , in agreement with prediction.
    Print ISSN: 0003-6951
    Digitale ISSN: 1077-3118
    Thema: Physik
    Publiziert von American Institute of Physics (AIP)
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  • 4
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    Benjamin Lax (2016)
    American Institute of Physics (AIP)
    Details
    Publikationsdatum: 2016-03-01
    Print ISSN: 0031-9228
    Digitale ISSN: 1945-0699
    Thema: Physik
    Publiziert von American Institute of Physics (AIP)
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  • 5
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    Sub-wavelength waveguide loaded by a complementary electric metamaterial for vacuum electron devices (2014)
    American Institute of Physics (AIP)
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    Publikationsdatum: 2014-10-10
    Beschreibung: We report the electromagnetic properties of a waveguide loaded by complementary electric split ring resonators (CeSRRs) and the application of the waveguide in vacuum electronics. The S-parameters of the CeSRRs in free space are calculated using the HFSS code and are used to retrieve the effective permittivity and permeability in an effective medium theory. The dispersion relation of a waveguide loaded with the CeSRRs is calculated by two approaches: by direct calculation with HFSS and by calculation with the effective medium theory; the results are in good agreement. An improved agreement is obtained using a fitting procedure for the permittivity tensor in the effective medium theory. The gain of a backward wave mode of the CeSRR-loaded waveguide interacting with an electron beam is calculated by two methods: by using the HFSS model and traveling wave tube theory; and by using a dispersion relation derived in the effective medium model. Results of the two methods are in very good agreement. The proposed all-metal structure may be useful in miniaturized vacuum electron devices.
    Print ISSN: 1070-664X
    Digitale ISSN: 1089-7674
    Thema: Physik
    Publiziert von American Institute of Physics (AIP)
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  • 6
    Digitale Medien
    Digitale Medien
    Velocity ratio measurements of a gyrotron electron beam (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 3789-3795 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A 140 GHz high-power gyrotron has recently been operated in a 14 T Bitter magnet to characterize emission as a function of magnetic field and beam current. The velocity ratio (or pitch angle) α=〈v⊥〉/〈v(parallel)〉 of the beam electrons is a critical parameter for high-efficiency gyrotron operation and was measured using a capacitive probe located in the beam tunnel before the cavity. The observed velocity ratio decreased as the beam current increased while the beam voltage and magnetic fields were held fixed. This decrease in α partially explains the reduced gyrotron efficiency observed at high-beam currents. The velocity ratio exhibited saturation effects as a function of both the beam current and the control-anode voltage, at low cathode magnetic field values. Particle code results show a decrease in α as a function of beam current that is consistent in magnitude with the observed values.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.348479
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  • 7
    Digitale Medien
    Digitale Medien
    Optical properties of semiconductor lasers with hydrostatic pressure (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 737-739 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The pressure dependence of the stimulated emission of a 1.3 μm In1−xGaxAsyP1−y (y=0.6) buried heterostructure laser has been measured up to 2.5 GPa. In this pressure range the laser output was tuned over 200 nm. The laser output energy varied linearly with pressure at a rate of (80±3) meV/GPa, corresponding to variation of the direct band gap of the InGaAsP active layer with pressure. From the measured energy shift and from calculations of the fractional volume change in the active layer for the strain conditions of the epilayer, a hydrostatic deformation potential of (−5.7±0.1) eV was obtained.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.355242
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  • 8
    Digitale Medien
    Digitale Medien
    Metalorganic molecular beam epitaxy of (In)GaAsN with dimethylhydrazine (2002)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 91 (2002), S. 56-64 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Single layers and superlattices of GaAsN/GaAs and InGaAsN/GaAs were grown using metalorganic molecular beam epitaxy with dimethylhydrazine, trimethylindium, triethylgallium, and conventional arsenic sources. Nitrogen incorporation into the solid was investigated as a function of the substrate temperature and fluxes. The nitrogen incorporation kinetics and growth mechanism have been modeled by assuming formation of an adduct arising from reactions between triethylgallium and dimethylhydrazine, while neglecting reactions between precursors of trimethylindium and dimethylhydrazine. The model accounts for the experimentally observed relationship between growth rates and nitrogen incorporation in GaAsN and InGaAsN. Our experiments show that the absolute arsenic flux and the As/N flux ratio play a critical role in the growth of single phase GaAsN. © 2002 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1419206
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  • 9
    Digitale Medien
    Digitale Medien
    High-power operation of a 170 GHz megawatt gyrotron : The 38th annual meeting of the Division of Plasma Physics (DPP) of the American Physical Society (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1907-1914 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Recent gyrotron oscillator experiments have achieved record powers at 170 GHz. Single mode emission with a peak output power of 1.5 MW and an efficiency of 35% has been measured. The experiment is based on a resonant TE28,8,1 cylindrical cavity situated in a 6.7 T magnetic field. Microwaves are generated in the cavity by an 83 kV annular electron beam produced by a triode-type magnetron injection gun that is capable of currents up to 50 A. Megawatt power levels with efficiencies between 30%–36% have been measured over a wide range of operating parameters for the TE28,8,1 mode. Similar results were also achieved in the neighboring TE27,8,1 mode at 166.6 GHz, and the TE29,8,1 mode at 173.5 GHz. The high output power is the result of a carefully designed electron gun with low perpendicular velocity spread (6%–10%) and a novel cavity with an output iris that is less prone to mode competition. These results are in good agreement with nonlinear multimode simulations. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.872334
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  • 10
    Digitale Medien
    Digitale Medien
    State-to-state rotational cross sections in vibrational modes. Application to the infrared Q-branch profile for the (11 10)I←(00 00) 12C16O2 bending band (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 3747-3753 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Direct connection between spectroscopic relaxation cross sections and appropriate state-to-state rotational cross sections in vibrational modes enables one to introduce convenient energy corrections to the sudden approximation. Since the angular momentum coupling photon–rotation–vibration is properly taken into account, this approach applies to stretching as well as bending bands. Diode laser experiments have been made for pure 12C16O2 in the infrared Q branch of the (11 10)I←(00 00) band in order to investigate the effect of collisional line mixing on the spectral profile. The energy corrected sudden scaling law is used within the present theoretical approach for both the inversion of j→0 basis cross sections from broadening data and the calculation of line-coupling coefficients. Resulting absorption profiles are in good agreement with measured values without the need for the introduction of any ad hoc decoupling factor for the considered bending band.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.464053
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