  5-cell elliptical cavities are chosen for the main linac of China Accelerator
Driven sub-critical System in the medium energy section. Each cavity is driven
by one fundamental power coupler delivering RF power up to 150 kW. A single
window, coaxial type coupler satisfying high power requirements, class 10 clean
room assembly with cavity and low heat load simultaneously was designed. This
paper gives the details of RF design, external Q calculation and thermal
analysis as well as multipacting simulations of the coupler.
