RF Window problems - September 2009

Shortly after we have achieved very good RF processing results in September 2009, we had a serious RF breakdown event at the RF window. This RF window separates the RF waveguide section at SF6 overpressure from the RF cavity at high vacuum.

In short, while running the klystron at about 7.5 MW output power a breakdown event occurred at the vacuum site of the RF window. We installed photodiodes to monitor breakdown light flashes from the RF cavity and from the RF window. At this specific event the light output from the window was evident. After this event, we had to turn the RF power level down to 1 MW and even then small discharges were appearing each pulse. RF processing did not improve this situation and lead to the conclusion that the RF window has been damages and had to be replaced.

We decided to replace the current CPI RF window of type VWX-1053 with a pillbox type RF window. After consulting some manufactures, we have ordered a RF window from CML Engineering of type 3020-02. This window has higher specifications in terms of peak and average RF power level and therefore will be more reliable. At the end of November 2009 this RF Window and adapter piece has been delivered.

The RF window that was installed originally.
The new RF window of CML Engineering installed in the RF section. The connection at the bottom is to the adapter piece for the connection to the RF input coupler of the RF cavity.
Side view of the RF window.