Some operational characteristics of CEBAF RF windows at 2K

A CEBAF superconducting rf cavity was instrumented to examine RF window behavior at 2K. Of special interest was window performance at levels of cavity power dissipation considerably above normal operating conditions. A variety of transient electronic activity was observed to occur at or near the rf window, including the emission of light, a precipitous increase in reflected power, and interesting cooperative effects between the window and cavity. Typically, the initiation of this activity at the window is correlated with the presence of a high X-ray and energetic electron flux at the window produced by the cavity. Electronic activity at the window can occasionally trigger the sudden disappearance of all stored energy in the cavity, herein referred to as an “electronic quench”. Variable delays of up to 40 μsec have been observed between the onset of window activity and the decay of the cavity field, which can occur in less than 200 nsec and is always accompanied by an intense pulse of X-rays. When the cavity is off resonance with negligible stored energy, rf fields at the window can be increased even further without the appearance of these effects