Direct, high power TE01-HE11 mode converters in overmoded, circular corrugated waveguide (70 GHz, I.D. = 27.79 mm) with periodic curvature distortions in one plane have been optimized by numerically integrating the corresponding coupled-mode differential equations with new, generalized coupling coefficients. Since at appropriate corrugation depth the 'unwanted mode conversion to the surface modes TE11 -<EH11 and TE21+EH21 is negligible, it is possible to design short mode transducers with high conversion efficiency. Both, the input mode TE01 and the output mode HE11, have very low currents and electric fields at the waveguide wall (volume modes). Thus, the mode transformer shows very high power carrying capability by avoiding waveguide arcing at flange connections. The overall conversion efficiency was calculated to be 97.44% for a 3λΒ, and 98.40%for a 4λΒ mode converter, ohmic losses are included.