New alcator C-Mod rotated 10° 4-strap ICRF antenna

We have developed a design for a new rotated 4-strap ICRF antenna. The design is based on a modification of the existing C-Mod antennas with the antenna rotated 10deg such that the entire structure is perpendicular to total magnetic field. This rotation is implemented in an attempt to reduce ICRF impurity production. The rotation results in an antenna with less surface area than the previous antennas and therefore a higher power density will be obtained for a given input power of 3 MW. The power density would reach 15 MW/m2, near the world record power density obtained in Tore Supra. We will describe the RF of this new design. The RF analysis was accomplished using the CST computer code. The fields were studied to minimize E field breakdown in the feed system and to accomplish the symmetry required for reduced impurity production in the four straps.