  The construction of the 60-MeV proton linac has started as a low-energy front
of the KEK/JAERI Joint Project for a high-intensity proton accelerator facility
at KEK. The accelerating frequency is 324 MHz. Five UHF klystrons are used as
an rf source; their ratings have a maximum power of 3 MW, a beam pulse width of
a 700 micro-sec (an rf pulse width is 650 micro-sec) and a repetition rate of
50 pps. We have manufactured a proto-type rf source (a power-supply system with
a modulating-anode pulse modulator and prototype klystrons). In this paper, the
specifications and developments of the rf source, including the WR-2300
waveguide system, are summarized. During the manufacturing process, strong
oscillations due to back-going electrons from the collector were observed. This
phenomenon was analyzed both experimentally and theoretically. We have tested
up to an output power of nearly 3 MW, and succeeded to test the DTL hot-model
structure.
