Mode Conversion Losses in Expansion Units for ITER ECH Transmission Lines
Name
10762_2015_190_ReferencePDF.pdf
Size
1.9 MB
Format
Adobe PDF
Checksum (MD5)
60eeeeb07b4ca4a8b932f5d68b3bcdd9
Author(s)
Hanson, G. R.
Schaub, Samuel Clay
Shapiro, Michael
Temkin, Richard J
Date Issued
August 2015
Journal
Journal of Infrared, Millimeter, and Terahertz Waves
Publisher
Springer US
Citation
Schaub, S. C., M. A. Shapiro, R. J. Temkin, and G. R. Hanson. “Mode Conversion Losses in Expansion Units for ITER ECH Transmission Lines.” J Infrared Milli Terahz Waves 37, no. 1 (August 16, 2015): 72–86.
Version
Author's final manuscript
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 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.
MIT Department
Massachusetts Institute of Technology. Department of Physics
Massachusetts Institute of Technology. Plasma Science and Fusion Center
Terms of Use
Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use.
Persistent DSpace Link
DOI of Published Version
https://doi.org/10.1007/s10762-015-0190-4
