PROGRESS TOWARD NLC/GLC PROTOTYPE ACCELERATOR STRUCTURES*

The accelerator structure groups for NLC (Next Linear Collider) and GLC (Global Linear Colliders) have successfully collaborated on the research and development of a major series of advanced accelerator structures based on room-temperature technology at X-band frequency. The progress in design, simulation, microwave measurement and high gradient tests are summarized in this paper. The recent effort in design and fabrication of the accelerator structure prototype for the main linac is presented in detail including HOM (High Order Mode) suppression and design of HOM couplers and fundamental mode couplers, optimized accelerator cavities as well as plans for future structures. HIGH GRADIENT TEST STRUCTURES Since 2000, more then thirty structures with different length, aperture, phase advance and coupler design have been built and tested at the NLCTA. [1] Through the thorough comparison and analysis we have selected the following main accelerator parameters: 60 cm of length, 5π/6 phase advance /cell, low group velocity with optimal attenuation factor of 0.5-0.6 for optimal RF efficiency. Figure 1: Maximum surface field for three types structures at unloaded gradient of 65 MV/m (left) and high power test results for eight structures (right). The parameters of A (H60VG3S18), B (H60VG3S17) an