Feasibility study of a HOM IOT for TESLA

For the TESLA linear collider 1.3 GHz RF sources with 10 MW peak power and about 70% efficiency are needed. As an alternative to the development of a multibeam-klystron, we investigate the feasibility of an IOT (inductive output tube). This is a very compact RF source: the time structure of the beam is produced by a gated emission cathode and the output cavity is directly adjacent to the anode. Unlike IOTs, conventional klystrons lose some of their design efficiency when they are operated below saturation, because only the RF component of the beam is reduced and not the DC beam current. In contrast to this the cathode current of an IOT is controlled by the drive power. In order to keep the gun voltage low, we plan to investigate a device with a hollow beam where the output cavity is excited in a higher order mode (HOM), as was recently suggested by CPI. Computer simulations are carried out with the CAD-system MAFIA. First, an existing Klystrode^TM IOT built by CPI is analysed. Simulation results will be shown and compared to experimental data. Based upon this experience, a design strategy is discussed for the HOM IOT