High-Efficiency, High Average Power Inductive Output Tubes

Better RF sources are required for ion, proton, and electron accelerators and colliders. Only klystrons are currently available; however, they are very large and expensive at frequencies below 1 GHz. Smaller, less expensive, and higher efficiency sources are required for new programs. Inductive output tubes operate in this frequency range, but they cannot provide sufficient power and efficiency because of grid fabrication issues and inherently low gain. Calabazas Creek Research Inc. (CCR) investigated multiple beam technology and an innovative power splitter in conjunction with a 3rd harmonic drive on the grid to increase the RF power of inductive output tubes (IOTs). The program investigated technologies to drive the multiple guns at the same phase and amplitude. CCR analyzed the thermomechanical requirements of the gun grids to determine if lower cost, metal grids could be used. The program investigated techniques to increase the efficiency above 80%. In Phase I program, it was determined that the efficiency could be increased to approximately 90% using 3rd harmonic RF power to drive the electron guns. Beam simulations and thermomechanical analysis determined that moly grids could replace pyrolytic graphite grids, significantly reducing both cost and risk. An input coupler design was developed that uniformly drives all electron guns in a dramatically simpler and lower cost method than current technology. The Phase I design will be optimized, and a prototype multiple beam IOT capable of producing 200 kW of average power at 700 MHz will be built and tested. Multiple beam IOTs would be applicable to a number of new accelerator systems, including the Advanced Photon Source upgrade, India Spallation Source, and eRHIC. It would also be applicable for industrial, medical, and security applications, including water purification, heating, security scanning, and medical imaging and cancer treatment. These RF sources would dramatically reduce both construction and operating cost.