High-power input coupler with a cylindrical alumina window

A high-power RF-input coupler has been installed in the TRISTAN alternating periodic structure cavity operating at 508 MHz. The structure, high power characteristics and long term performance of the coupler are described. It has a cylindrical alumina window coated with TiN of 60-AA thickness and feeds a power of 225 kW (CW) to the cavity. In an early stage of development, the multipactoring discharge of the window was a primary problem. After the coating, the window discharge was not observed. A total of 112 couplers has been installed in the TRISTAN ring and successfully operated for about 17000 h since the spring of 1985. The most serious trouble with the operation was a failure of the loop. This problem was discovered after about 5000 h of operation. Improvements to the coupler including the loop have been made.<>