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  • 1
    Electronic Resource
    Electronic Resource
    Generation of the Gaussian-like HE11 mode from gyrotron TEOn mode mixtures at 70 GHz (1985)
    Springer
    International journal of infrared and millimeter waves 6 (1985), S. 459-470 
    Details
    ISSN: 1572-9559
    Keywords: high-power millimeter waves ; gyrotron ; electron cyclotron resonance heating (ECRH) ; overmoded waveguide systems ; mode conversion ; linearly polarized narrow pencil beam
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract This work reports calculations and measurements on mode converters for the transformation of TEOn gyrotron mode mixtures (primarily TEO2) into the linearly polarized HE11 hybrid mode at 70 GHz. This mode is ideal for quasi-optical launching systems for ECRH of plasmas. Mode transducers with axisymmetric radius perturbations convert the gyrotron TEOn mode composition into the TEO1 mode. Proper matching of the phase differences between the various modes and of the perturbation amplitudes of the several converter sections is required. The TEO1 wave is used for long-distance transmission through smooth-walled overmoded waveguides. A mode converter with constant diameter and periodically perturbed curvature transfers the unpolarized TEO1 mode into the polarized TE11 wave. The experimentally determined ΣTEOn-to-TEO1 conversion efficiency is (98.5±1)% (99% predicted) while the TEO1-to-TE11 transformer has a (94±2)% efficiency (93% theoretically); ohmic losses are included. The “Gaussian-like” HE11 mode with axisymmetric power distribution and almost no cross polarization is produced in a circumferentially corrugated TE11-to-HE11 mode transducer with a measured conversion efficiency of (98.3±1.5)% (98.5% predicted). The overall efficiency of the complete mode converter system in the desired mode was determined to be (91±2.5)%. High-power operation (200kW, 100ms) has been successfully demonstrated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01010037
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Computer-aided analysis and design of corrugated TE11 to HE11 mode converters in highly overmoded waveguides (1985)
    Springer
    International journal of infrared and millimeter waves 6 (1985), S. 577-597 
    Details
    ISSN: 1572-9559
    Keywords: high-power millimeter waves ; gyrotron ; electron cyclotron resonance heating ; overmoded waveguide systems ; mode conversion ; linearly polarized narrow pencil beam
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A theoretical and experimental study of TE11-to-HE11 mode conversion in highly oversized waveguides is given. The balanced HE11 hybrid mode propagating in a circumferentially corrugated circular waveguide is in many respects ideal for effective electron cyclotron resonance heating of fusion plasmas with high-power gyrotrons. At an aperture antenna it exhibits desirable radiation characteristics such as linear polarization with very low cross polarization and axisymmetric power distribution with low sidelobe levels. This “Gaussian-like” mode can be generated from a TE11 mode by means of a corrugated mode converter in which the depth of the annular slots is tapered gradually from one-half to one-quarter wavelength. Computer-aided optimization of converter length, shape of corrugations, and of non-linear slot depth variation for 28 GHz- and 70 GHz-transducers was achieved with a scattering matrix formalism employing the modal field expansion technique (Modular Analysis Concept). In both cases the measured conversion efficiency of (98.5±0.5)% and the experimental values of the maximum cross polarization (below −28 dB) are in very good agreement with the predicted values. High-power operation was successfully demonstrated using pulsed 28 GHz- and 70 GHz-VARIAN gyrotrons (200 kW).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01009672
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    TE03 to TE01 mode converters for use with a 150 GHz gyrotron (1987)
    Springer
    International journal of infrared and millimeter waves 8 (1987), S. 227-240 
    Details
    ISSN: 1572-9559
    Keywords: gypotron ; high-power millimeter waves ; electron cyclotron resonance heating (ECRH) ; overmoded waveguide systems ; rippled-wall mode converters
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Two-step high-power TE03-to-TE01 mode transducers (TE02 is the intermediate mode) were designed to transform the TE03 output mode of the 150 GHz KfK gyrotron into the fundamental circular symmetric TE01 mode for low-loss propagation and further conversion into the linearly polarized quasioptical HE11 mode. The advanced perturbation structures of the ruppled-wall mode converters (with input- and output-diameter D=27.8 mm) were optimized by numerically solving the proper coupled-wave differential equations. The overall TE03-to-TE01 conversion efficiency at 150 GHz was calculated to be η0=99.1% for a long converter (total length L=2.67 m) and η0=97.8% for a short converter (L=1.07 m); ohmic attenuation is included. The corresponding theoretical bandwidth (for η≧95%) is ±1.4 GHz and ±2 GHz, respectively. Low-power experimental data are in excellent agreement with these computed values.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01014556
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    Paper (German National Licenses)
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