17 GHz high gradient linac having stainless steel surfaces in the high intensity magnetic and electric field regions of the structure

To avoid surface erosion damage and to assist in understanding RF breakdown limitations imposed on high gradient linac operation, a gradient hardened structure is being fabricated having high temperature brazed and machined stainless steel surfaces located in the high E- field region of the beam apertures and in the high H-field regions of the racetrack shaped coupling cavities. The microwave design parameters and physical dimensions of this 17 GHz, 2pi/3 mode, 22-cavity structure were established specifically to allow comparison of its high gradient performance to that of a similar all-copper structure tested under identical conditions, using an existing 4X power amplifying, RF recirculating dual ring system. Use of the 6X thicker skin depth material, the resulting de-Q-ing effects and the minimal reduction of beam energy (2%) associated with the strategically located lossy surfaces are discussed; fabrication techniques are described; and design parameters of the gradient hardened linac and the 17GHz power amplifying system are presented.