High-power klystrons for the Next Linear Collider

The Stanford Linear Accelerator Center (SLAC) version of the 1 TeV Next Linear Collider (NLC) requires a 4:1 increase in drive frequency, from the 2.85 GHz of the .1 TeV Stanford Linear Collider (SLC) to 11:4 GHz for the NLC. More than eight years have gone into the development of a new 75-MW klystron for powering the NLC. The increase in power density and surface RF gradient at the higher frequency have rendered previous RF window and circuit designs unusable. Following numerous catastrophic gun, cavity, and window failures, new designs have evolved that solved the problems. As history's most ambitious klystron development enters its last year, the results includes a robust 75-MW peak power solenoid-focused, 50% efficient klystron. Not far behind is a 60-75-MW periodic permanent magnet (PPM)-focused 60% efficient version that will reduce the NLC electric power bill by tens of millions of dollars per year.