A recently published modeling and computer simulation design of a paper on the externally connected traveling wave antenna (TWA) for DIII-D [1] was primarily concerned with the effects of plasma loading and changes in plasma conditions on the desired TWA performance. To simplify and clearly study the effects due to plasma, this modeling made full use of idealized coaxial or stripline components with precise impedances, lengths, and non-perturbing point contacts at junctions, tees and crosses, etc. Furthermore, previous recirculator and variable directional coupler modeling and analyses were based on ideal coupler theory [1]. In contrast, this paper presents and validates a complete rf engineering design for a buildable version of that externally connected TWA [1]. This TWA design is validated against rf voltage breakdown and rf current heating using a 1.5-2 MW at 60-120 MHz transmitter and the four-element antenna in the 180 degree toroidal port in DIII-D. Component weight, mechanical strength and rf wave reflection from and transmission through practical size interfaces are considered. Finally, a complete design of a recirculator with a variable directional coupler is presented. The directional coupler uses a phase shifter configuration to optimize both the coupling factor and the recirculator traveling wave resonance. The design is validated against the anticipated frequency dependent variation of rf power flow, insertion loss, directivity and VSWR in the hybrid variable directional coupler, TWA and interconnecting coaxial line.

*Work supported by U.S. Department of Energy Contracts DE-AC03-89ER51114 and DE-AC05-96OR22464.
[1]D.A. Phelps, et al., "Advantages of Traveling Wave Resonant Antennas for Fast Wave Heating Systems," 12th Top. Conf. on Radio Frequency Power in Plasmas, Savannah, Georgia, 1997.