SLAC modulator availability and impact on SLC operation

In 1991, the Stanford Linear Collider (SLC) operated, with diverse accelerator systems, at 60% availability. In the more auspicious 1992 and 1993 runs availability improved to over 80%. For the 94/95 run, the availability was also about 80%. Ignoring the eclectic-accelerator, this discussion will assess the dependence of the SLC on the reliability and hence, availability, of 244 klystron modulator systems that provide power to the machine´s bunched-particle beams. Klystron modulator availability must be 99% for the accelerator to function at the 75% level. Fortunately, an excess of modulator/klystrons provides some redundancy and, therefore, allows some freedom from the requirement that all 244 systems perform simultaneously. There are, however, 15 specific exceptions. They populate strategic positions at the injector, damping rings, and positron production area of the accelerator complex. These, systems-without-spares, directly influence overall accelerator availability. Their calculated availability as an ensemble is 90%, but by chance they have operated at up to 99%. Individually, a malfunction can bring an experimental program to a halt. The discussion includes a description of several improvements to increase future availability for the modulator system