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Title: Mode Conversion Losses in Expansion Units for ITER ECH Transmission Lines

Abstract

The ITER electron cyclotron heating transmission lines will consist of 63.5 mm diameter corrugated waveguides, each carrying 1 MW of 170 GHz microwaves. These transmission lines must include expansion units to accommodate expansion and contraction along the path from the gyrotron microwave sources to the tokamak. A numerical mode matching code has been developed to calculate power losses due to mode conversion of the operating mode, HE11, to higher order modes as a result of the radial discontinuities in a sliding joint. Two expansion unit designs were evaluated, a simple gap expansion unit and a more complex tapered expansion unit. The gap expansion unit demonstrated loss that oscillated rapidly with expansion length, due to trapped modes within the unit. The tapered expansion unit has been shown to effectively suppress these trapped modes at the expense of increased fabrication complexity. In a gap expansion unit, for a waveguide step size of 2.5 mm, loss can be kept below 0.1% to a maximum expansion length of 17 mm. Expansion units without corrugation on interior walls were also evaluated. Expansion units that lack corrugations are found to increase mode trapping within the units, though not beyond useful application. The mode matching code developedmore » in this paper was also used to estimate mode conversion loss in vacuum pumpouts for the ECH lines; the estimated loss was found to be negligibly small.« less

Authors:
; ; ;
Publication Date:
DOE Contract Number:  
FC02-93ER54186
Research Org.:
Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States). Plasma Science and Fusion Center
Sponsoring Org.:
USDOE Office of Science (SC), Fusion Energy Sciences (FES)
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY
OSTI Identifier:
1878761
DOI:
https://doi.org/10.7910/DVN/6CQP6M

Citation Formats

Schaub, S. C., Shapiro, M. A., Temkin, R. J., and Hanson, G. R. Mode Conversion Losses in Expansion Units for ITER ECH Transmission Lines. United States: N. p., 2018. Web. doi:10.7910/DVN/6CQP6M.
Schaub, S. C., Shapiro, M. A., Temkin, R. J., & Hanson, G. R. Mode Conversion Losses in Expansion Units for ITER ECH Transmission Lines. United States. doi:https://doi.org/10.7910/DVN/6CQP6M
Schaub, S. C., Shapiro, M. A., Temkin, R. J., and Hanson, G. R. 2018. "Mode Conversion Losses in Expansion Units for ITER ECH Transmission Lines". United States. doi:https://doi.org/10.7910/DVN/6CQP6M. https://www.osti.gov/servlets/purl/1878761. Pub date:Tue Oct 16 00:00:00 EDT 2018
@article{osti_1878761,
title = {Mode Conversion Losses in Expansion Units for ITER ECH Transmission Lines},
author = {Schaub, S. C. and Shapiro, M. A. and Temkin, R. J. and Hanson, G. R.},
abstractNote = {The ITER electron cyclotron heating transmission lines will consist of 63.5 mm diameter corrugated waveguides, each carrying 1 MW of 170 GHz microwaves. These transmission lines must include expansion units to accommodate expansion and contraction along the path from the gyrotron microwave sources to the tokamak. A numerical mode matching code has been developed to calculate power losses due to mode conversion of the operating mode, HE11, to higher order modes as a result of the radial discontinuities in a sliding joint. Two expansion unit designs were evaluated, a simple gap expansion unit and a more complex tapered expansion unit. The gap expansion unit demonstrated loss that oscillated rapidly with expansion length, due to trapped modes within the unit. The tapered expansion unit has been shown to effectively suppress these trapped modes at the expense of increased fabrication complexity. In a gap expansion unit, for a waveguide step size of 2.5 mm, loss can be kept below 0.1% to a maximum expansion length of 17 mm. Expansion units without corrugation on interior walls were also evaluated. Expansion units that lack corrugations are found to increase mode trapping within the units, though not beyond useful application. The mode matching code developed in this paper was also used to estimate mode conversion loss in vacuum pumpouts for the ECH lines; the estimated loss was found to be negligibly small.},
doi = {10.7910/DVN/6CQP6M},
journal = {},
number = ,
volume = ,
place = {United States},
year = {2018},
month = {10}
}

Works referencing / citing this record:

Mode Conversion Losses in Expansion Units for ITER ECH Transmission Lines
journal, August 2015