Ech Experiments On Atf

Several electron cyclotron heating (ECH) experiments have been completed on the Advanced Toroidal Facility (ATF) at Oak Ridge National Laboratory (ORNL) under a variety of operating conditions and launch polarizations. ECH power is launched using a polarization‐controlled beam launcher and microwave detectors are used to measure absorption of first‐pass and multiply‐reflected power. Measurements show that first‐pass absorption efficiency at low plasma density is highly dependent on magnetic field, polarization, and plasma conditions. Wave polarization rotation has been detected; it is caused by the large magnetic field shear on ATF. Detector signals indicate that absorption efficiency is relatively high for medium plasma density at either fundamental or second harmonic operation. Plasmas have also been sustained using the third harmonic cyclotron resonance where absorption efficiency is much lower. Gyrotron power modulation and turn‐off experiments have been performed to study power deposition and transport using plasma diagnostics. These experiments show that power absorption is fairly efficient. However, the power deposition profile is rather broad despite the relatively narrow launcher beam. This effect can be attributed to several factors including the broad extent of the resonant surface and the ∼45% of power contained in both low‐level sidelobes outside the launcher beam and in the wrong plasma mode.