Design and high-power test of a TE11-mode X-band RF window with taper transitions

A TE11-mode X-band RF window capable of passing RF power above 70 MW with 500 ns duration has been developed for installation to a pulse high-power klystron. The window comprises: (a) TE10(WRJ-10)-TE11-mode (WC-5) converters, (b) circular-waveguide tapers and (c) an alumina ceramic with a circular-waveguide frame. This paper describes its design and high-power performance. The basic design concept is to reduce the RF field strength on the ceramic surface by increasing the diameter of its ceramic part compared to an ordinary pill-box-type window. The design of its RF structure was achieved by using a circuit model, and was confirmed by numerical simulations. The dimensions of the window necessary to obtain good RF transmission were found by changing the length of the circular-waveguide frame. A high-power test using a traveling-wave resonator has been successfully carried out up to a circulating power of 100 MW with a 300 ns pulse width. The tests showed that the break-down limit of the electric-field strength on the ceramic surface was about 8 kV/mm. This limit was the same as in the case of S-band pill-box window experiments