Observations of multipactor in a large klystron

Evidence was found of multipactor discharges occurring in the output cavity and waveguide of a large klystron (1.3 Mw peak, 150 kW average 805 MHz). High energy electron bombardment in many areas of the cavity and waveguide was found and investigated by recording the X rays generated, by providing windows for visual observation, and by manipulating the magnetic fields. Slides will be shown of some of the X-ray films, and of color photographs of fluorescent surfaces and incandescent particles in the cavity. In general, the cavity was brightly lit by the various discharges, while the beam tunnel was relatively dark, both visually and by X-ray recording.