Coupling of tilting Gaussian beam with hybrid mode in the corrugated waveguide |
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Authors: | K Ohkubo S Kubo H Idei M Sato T Shimozuma and Y Takita |
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Institution: | (1) National Institute for Fusion Science, Furo-cho, Chikusa-ku, 461-01 Nagoya, Japan |
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Abstract: | The mode-conversion loss in the matching between the gaussian beam emanated from the gyrotron and the hybrid mode in the circular
corrugated waveguide with the diameter of 2a is discussed. By numerical calculation, it is found that the loss considerably increases and optimum waist sizew
0 changes when TEM00 mode with the wavelength λ is injected with offset or tilt. By fitting numerical data to the polynomial function, it becomes
evident that the scaling formulas of the losses for the off-axis shiftr
d
and for the tilt angle θ are derived to be 2.3(r
d
/a)2 – 2.2(r
d
/a)4 and 3.9(aα/λ)2 – 5.6(aθ/λ)4 for fixedw
0/a=0.643, respectively. To keep the mode-conversion loss ≤1% for the frequency of 168 GHz and 2a=88.9 mm, tilting angle and offset should be less than 0.1 degrees and 2.9 mm, respectively. |
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Keywords: | guassian beam hybrid mode HE11 mode corrugated wave guide coupling gyrotron electron cyclotron heating |
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