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Description
Design features and test results of a multibeam inductive output tube (MB-IOT) that produces over 1.2 MW peak power at 704 MHz with over 65% efficiency will be presented. This is a collaborative effort between Thales Electron Devices and Communications & Power Industries to design and fabricate a new RF source for the European Spallation Source (ESS). The first prototype has been designed and built. The device contains 10 beams generated by 10 gridded guns, focused by a single solenoid and deposited in 10 isolated collectors. The beam-wave interaction takes place inside a coaxial cavity. An input circuit evenly distributes the single input drive power to the individual guns. Initial test at CERN demonstrated output power of 1.2 MW peak, efficiency of 69.8%, and gain of 21.4 dB at 1 ms operation, with 45 kV cathode voltage and with 98% beam transmission. Efficiency was also maintained above 60% down to 680 kW reduced power level. When the pulse length was increased to 4 ms, instability in the RF output pulse developed as the result of a mechanical contact issue in the output window. An improved design has been assembled on to the tube and the repaired prototype has been shipped back to CERN. Subsequent testing is expected in September 2018 to demonstrate full compliance to the ESS requirements.
