Measuring power loss in DIII-D ECH waveguides with arrays of temperature sensors*

The DIII-D National Fusion Facility utilizes megawatt-class gyrotrons for electron cyclotron heating (ECH) and current drive (ECCD). Corrugated waveguides, 70-80

meters long with 31.75 mm inner diameter, transmit 110 GHz radio frequency (RF) waves from gyrotrons to the tokamak. Understanding the physics effects of ECH/ECCD

processes relies on accurate estimates of injected ECH power, which require precise measurements of RF transmission losses. DIII-D has expanded its methods for assessing

losses, moving beyond comparing power measurements between dummy loads near the gyrotrons and those near the tokamak. An array of resistance temperature

detectors (RTDs) measures the temperature rise of one of DIII-D’s waveguides during gyrotron pulses, which allows estimation of the power lost to waveguide heating. This

RTD array now interfaces with a python GUI for real-time temperature monitoring during plasma operations. This setup improves the spatial resolution of waveguide

heating, enabling early detection of potential damage and continual tracking of transmission characteristics over time.