Anomalous electron loading in SLAC 5045 klystron and relativistic klystron input cavities

Studies of RF breakup and instability in the SLAC (Stanford Linear Accelerator Center) 5045 klystrons have revealed that many production klystrons show loading of the input cavity by low-energy electrons even under cold-cathode no-beam conditions. Sometime after the onset of the RF drive pulse, the input cavity absorbs a portion of the incident RF drive that would otherwise be reflected from the not-beam-loaded cavity. This power absorption is a function of drive level and of axial magnetic field surrounding the cavity. No power absorption is present when the axial magnetic field is zero. This same phenomenon has been observed in the input cavity of relativistic klystron experiments being conducted as part of the SLAC-LBL-LLNL development program. The phenomenon may be associated with RF breakup and RF instability in SLAC 5045 klystrons, and with unstable pulse shortening in the relativistic klystron experiments. Some old and new observations of microwave beam device malfunctions that probably are associated with low-energy electron fluxes in the vacuum environments of microwave power devices are outlined