  We are currently operating the front end of the accelerator production of
tritium (APT) accelerator, a 7 MeV radio frequency quadrapole (RFQ) using
three, 1.2 MW CW klystrons. These klystrons are required and designed to
dissipate the full beam power in the collector. The klystrons have less than
1500 operational hours. One collector has failed and all collectors are
damaged. This paper will discuss the damage and the difficulties in diagnosing
the cause. The collector did not critically fail. Tube operation was still
possible and the klystron operated up to 70% of full beam power with excellent
vacuum. The indication that finally led us to the collector failure was
variable emission. This information will be discussed. A hydrophonic system was
implemented to diagnose collector heating. The collectors are designed to allow
for mixed-phase cooling and with the hydrophonic test equipment we are able to
observe: normal, single-phase cooling, mixed-phase cooling, and a hard boil.
These data will be presented. The worst case beam profile from a collector
heating standpoint is presented. The paper will also discuss the steps taken to
halt the collector damage on the remaining 350 MHz klystrons and design changes
that are being implemented to correct the problem.
