  Initial test results of an L-band multi-beam klystron with parameters
relevant for ILC are presented. The chief distinction of this tube from MBKs
already developed for ILC is its low operating voltage of 60 kV, a virtue that
implies considerable technological simplifications in the accelerator complex.
To demonstrate the concept underlying the tubes design, a six-beamlet quadrant
(a 54 inch high one-quarter portion of the full 1.3 GHz tube) was built and
recently underwent initial tests, with main goals of demonstrating rated gun
perveance, rated gain, and at least one-quarter of the full 10-MW rated power.
Our initial three-day conditioning campaign without RF drive (140 microsec
pulses @ 60 Hz) was stopped at 53% of full rated duty because of time-limits at
the test-site; no signs appeared that would seem to prevent achieving full duty
operation (i.e., 1.6 msec pulses @ 10 Hz). The subsequent tests with 10-15
microsec RF pulses confirmed the rated gain, produced output powers of up to
2.86 MW at 60 kV with high efficiency and 56 dB gain, and showed acceptable
beam interception. These results suggest that a full version of the tube should
be able to produce up to 11.5 MW. Follow-on tests are planned for later in
2015.
