A mode-transforming polarization-rotatable launcher for the ATF (Advanced Toroidal Facility) fusion experiment

Abstract

The Advanced Toroidal Facility (ATF) fusion energy experiment at the Oak Ridge National Laboratory (ORNL) requires high-power microwaves for startup and plasma heating. Power from a gyrotron oscillator tube at 53.2 GHz will be used to ionize and heat the plasma by the electron cyclotron heating (ECH) process. The confining magnetic field of the device is either 0.95 or 1.9T. The gyrotron tube generates 200 kW in the TE/sub 02/ mode, which is transported in an overmoded 6.35-cm-diam circular waveguide to the ATF vacuum vessel. The launcher consists of a mode-converting Vlasov section, which converts the nonpolarized TE/sub 02/ wave into a linearly polarized narrow beam. The beam reflects off a tiled spherical reflector grating and is focused at the center of the plasma. The polarization can be rotated to optimize the absorption efficiency by rotating the grating in the spherical reflector. Overall system efficiency is kept high by making the twist reflector large enough to catch the Vlasov converter sidelobe power, which is partially due to mode conversion in the waveguide system. The launcher design and laboratory measurements are discussed. 3 refs., 3 figs