TRAVELLING WAVE AND STANDING WAVE SINGLE CELL HIGH GRADIENT TESTS

Accelerating gradient is one of the crucial parameters affecting design, construction and cost of next-generation linear accelerators. Operating accelerating gradient in normal conducting accelerating structures is limited by rf breakdown. In this paper we describe an experimental setup for study of these limits for 11.4 GHz travelingwave and standing-wave accelerating structures. The setup uses matched mode converters that launch the circular TM01 mode into short test structures. The test structures are designed so that the electromagnetic fields in one cell mimic the fields in prototype structures for the Next Linear Collider. Fields elsewhere in the test structures and in the mode converters are significantly lower than in this single cell. This setup allows economic testing of different cell geometries, cell materials and preparation techniques with short turn around time. Here we present design considerations and describe planned experiments.