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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.

Techniques for cleaning and conditioning the vacuum vessel of the Advanced Toroidal Facility (ATF) and its internal components are described. The vacuum vessel cleaning technique combines baking to 150 °C and glow discharges with hydrogen gas. Chromium gettering is used to further condition the system. The major internal components are the anodized aluminum baffles in the Thomson scattering system, a graphite‐shielded ICRF antenna, two graphite limiters, and a diagnostic graphite plate. Three independent heating systems are used to bake some of the major components of the system. The major characteristics used for assessing cleanliness and conditioning progress are the maximum pressure attained during bakeout, the results of gas analysis, and revelant plasma parameters (e.g., time to radiative decay). Details of the various cleaning and conditioning procedures and results are presented.