  For the baseline APT (Accelerator Production of Tritium) linac design, power
couplers are required to transmit 210-kW of CW RF power to the superconducting
cavities. These APT couplers operate at 700 MHz, have a coaxial design and an
adjustable coupling to the superconducting cavities. Since May 1999, we have
been testing couplers of this design on a room-temperature test stand. We
completed tests at transmitted-power and reflected-power conditions up to 1 MW.
We also tested the couplers with a portion of the outer conductor cooled by
liquid nitrogen. Under this latter condition, we studied the effects of
condensed gases on coupler performance. The results of these tests indicate
that the APT couplers are capable of delivering more than 500 kW to the
cavities. We are in the process of increasing the baseline coupler design
requirement to 420 kW of transmitted power to take advantage of this successful
development. In this paper, we describe the results of our high-power coupler
tests.
