Improvement of gun and klystron modulator of SPring-8 linac

The cathode emission currents in the gun of the SPring-8 linac have been sometimes insufficient, or uncontrolled accidental emissions have been rarely observed. We have suspected that the inadequate cathode temperature may have caused these cathode failures. To investigate these cathode failures, we have constructed a measuring system of the cathode temperatures and the cathode emission currents at the test stand. Diligent maintenance and improvement of the gun and klystron modulators have reduced each failure rate down to less than 10 events par year. However, we still have the following failures with the thyratron circuits: The thyratron heater and reserver power supplies sometimes present voltage instabilities due to the poor contact in their aged voltage sliders. The thyratron trigger drivers have been affected by the line voltage fluctuations to result in timing shifts of the output pulses. The thyratron (L-4888C) heater leads often deteriorate due to an unknown reason. These issues are under investigation. (author)