DESIGN AND FABRICATION OF INPUT RF COUPLER WINDOWS FOR THE SNS * Quan-Sheng Shu, Joe Susta, Guangfeng Cheng AMAC International Inc, Newport News, VA 23606 (USA) Steven Einarson, Todd. A. Treado, William C. Guss, and Michael Tracy Communication and Power Industries Inc. (CPI), Beverly, MA 01915-5595 (USA) Abstract The RF coupler was designed by AMAC to meet the specification requirements for the SNS accelerator project. CPI performed the manufacturing optimization. AMAC as primary contractor was awarded a contract by Jefferson lab to provide three SNS prototype coupler windows using AMAC-1 window assembly design. CPI performed the fabrication. Three AMAC-1 prototypes have been high RF power tested and qualified to SNS technical specifications by Jefferson Lab. This paper mainly focuses on the design optimization, key simulation results of HFSS, MAFIA, ANSYS, electron-multipacting program results, and the mechanical design features as well. The fabrication and the cold test are described in a separate presentation in this workshop. 1 INTRODUCTION The various applications of superconducting Radiofrequency (RF) Accelerators in many fields around the world have increased rapidly [1]. High power RF windows are critically important to the reliability of storage rings and linear accelerators. If a window breaks, an entire accelerator section will go from high vacuum up to air, causing a great deal of time and money in maintenance costs. High power RF couplers depend on the reliability of windows to provide the transition from air to vacuum in the RF line between the RF power sources to the accelerator cavities [2, 3, 4, 5]. The cost and complexity of RF couplers has grown dramatically in the last 10 years because of the difficulty in manufacturing these complex RF systems, and because of the mechanical, electrical, and thermal stresses the window must take during operation. At the same time, there is always the demand for RF systems that deliver higher power [6]. Under DOE’s support, AMAC developed coaxial RF windows and couplers, and successfully developed, designed and prototyped a 200kW CW high RF input power waveguide type window which was high RF power tested & qualified by Jefferson Lab through a CRADA. Based on these proven qualifications, AMAC and CPI (subcontractor) were awarded a contract to produce three prototype SNS high RF input power coupler windows. They were delivered; high RF power tested, and qualified to meet the SNS technical requirements. The SNS technical requirement are briefly listed in the following: VSWR: 1.05 or lower at 805 MHz Power input: 550 kW peak traveling wave Beam on pulse length: 1.0 ms RF on pulse length: 1.3 ms Pulse repetition rate: 60 Hz RF active duty factor: 8.7% Standing wave in full reflection: 4 MW (up to 150 s) Average power: 53 kW (with 10% margin) Maximum radiative heat loss to 2.1K circuit: 1 W Operating pressure: <5  10 -9 torr Radiation resistance at tip of antenna: 4  10 8 rads During the task of prototyping three SNS prototype coupler windows, we developed several design concepts, then performed evaluation and optimization of the relative merits based upon the following RF and mechanical considerations: (1) RF properties, (2) Design maturity, (3) Thermal and mechanical design for perimeter cooling * This work was partly funded by a US Department of Energy SBIR grant (No DE-FG02-99-ER82739),and a contribution from CPI.