In this paper, the electromagnetic design of a 10-MW-class high-temperature superconducting (HTS) wind turbine synchronous generator is discussed. The primary designed machine is modeled using a finite-element method, and the generator characteristics are obtained. As one of the most important characteristics of a generator is voltage harmonics contents, excitation field winding dimensions through sensitivity analysis are optimized in order to reduce voltage and magnetic field harmonics. Behavior of both the excitation field winding producing magnetic flux density and voltage harmonic components by varying HTS coil width and height is obtained. This paper shows that output voltage harmonics contents of the proposed generator are sensitive to the excitation field coil dimensions.