Update on Cooling for the ITER ECH Waveguide Transmission Line

The ITER Electron Cyclotron Heating (ECH) system provides 20 MW of microwave power from 24 gyrotron sources. The power is transmitted through evacuated, corrugated waveguide transmission lines. The aluminum waveguide is cooled by the attachment of water-cooled copper tubes. These are connected through a conductive graphite foil that is used to increase the heat transfer ability between the aluminum and copper. In the regions where the waveguide is joined to a miter bend or to another waveguide section via a coupling, the waveguide cannot be actively cooled due to coupling hardware. Waveguide sections near couplings and miter bends are modeled and subjected to heat loads based on ITER design specifications. The thermal analysis predicts the maximum waveguide temperature in these regions and the amount of axial thermal expansion of the waveguide.

In addition, testing is done to determine the thermal contact conductance (TCC) between copper and aluminum surfaces with and without several candidate thermal contact materials. These results are used in the finite element analysis to model the ability to transfer heat across interfaces. The TCC test results make it clear that there is significant heat transfer between separate components, as the TCC between components is greater than 5 kW/m²K without thermal contact material and greater than 30 kW/m²K when thin graphite foil is used to increase the heat transfer ability. Therefore miter bends and miter bend mirrors are included as necessary in the finite element model.