A RESCUE MODE FOR THE DIAMOND LIGHT SOURCE PRE-INJECTOR LINAC

The Diamond Light Source injector consists of a 100 MeV linac and a 3 GeV full-energy booster. The linac contains two S-band accelerating structures driven by two high-power klystrons. Details are presented in this paper of a new switching network in the linac waveguide, allowing either of the klystrons to drive the low-energy section of the linac while the other is repaired and run into a dummy load. This allows limited operation of the linac in the event of a failure in either klystron or modulator. THE NEED FOR A RESCUE MODE High power RF for the Diamond linac is generated by two Thales TH2100 S-band klystrons, each delivering 5 μs pulses of up to 20 MW at a repetition rate of 5 Hz. Since the start of Diamond operation in 2007 one klystron has powered bunchers and an accelerating structure, and the other has fed a second accelerating structure [1]. With the klystrons feeding the two structures independently, a failure of the klystron or modulator feeding the lower energy structure and bunchers renders the linac, and hence the injection system as a whole, inoperable. In the event of a failure of the higher-energy klystron or modulator, linac operation is still possible at a reduced energy. There have been several short-term interruptions to linac operation, including failure of a modulator thyratron and faults in several minor electronic components, but the greatest linac disruption so far has been the exchange of the two original klystrons for new tubes. Routine monitoring of tube perveance enabled one klystron to be replaced before failure during a scheduled machine shutdown after 19,600 hours of operation. Perveances of both klystrons in the months leading up to the exchange of klystron 2 are shown in Fig. 1.