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Author(s):
K. Ohkubo, S. Kubo, H. Idei, M. Sato, T. Shimozuma and Y. Takita
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Title:
Coupling of Tilting Gaussian Beam with Hybrid Mode in the Corrugated Waveguide
Date of publication:
Jan. 1997
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Key words:
guassian beam, hybrid mode, HE_11 mode, corrugated wave guide, coupling, gyrotron, electron cyclotron heating
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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 size omega_0 changes when TEM_00 mode with the wavelength lambda 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 shift gamma_d and for the tilt angle theta are derived to be 2.3(gamma_d/a)^2 -2.2(gamma_d/a)^4 and 3.9(a theta/lamba)^2 - 5.6(a theta/lambda)^4 for fixed omega_0/a=0.643, respectively. To keep the mode-conversion loss leq 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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