Characterizing EC Transmission Line Losses and Reflections at DIII-D

Electron cyclotron current drive is used in fusion devices to drive off-axis current to control instabilities and to improve confinement. Its efficiency plays into the overall efficiency when considering future fusion power plants. There are several significant loss mechanisms in the transport of the microwaves from the gyrotron to the target, including ohmic loss in the waveguide and miter bends, and reflection from the miter bends. Currently estimated losses are 1.5% per miter bend at DIII-D, which compounds significantly along paths that can have as many as 15 bends. At present, there is a disparity between the expected and measured power values at the dummy load. Through additional calorimetric measurements and waveguide temperature measurements, we will better quantify the losses and improve the estimate of the EC power launched into the tokamak. Additionally, gaining a better picture of reflection could provide an important tool to help avoid damage to the gyrotrons. The resulting improved understanding of energy transport from gyrotrons to the tokamak will facilitate optimization of future EC systems.



Work supported by the US Department of Energy under the Science Undergraduate Laboratory Internship (SULI) program and DE-FC02-04ER54698.