  Klystrons capable of 75 MW output power at 11.4 GHz have been under
development at SLAC for the last decade. The work has been part of the program
to realize all the components necessary for the construction of the Next Linear
Collider (NLC). The effort has produced a family of solenoid-focused 50 MW
klystrons, which are currently powering a 0.5 GeV test accelerator at SLAC and
several test stands, where high power components are evaluated and fundamental
research is performed studying rf breakdown and dark current production.
Continuing development has resulted in a Periodic Permanent Magnet (PPM)
focused 50 MW klystron, tested at SLAC and subsequently contracted for
manufacture by industry in England and Japan. A 75 MW version of that PPM
klystron was built at SLAC and reached 75 MW, with 2.8 microsecond pulses.
Based on this design, a prototype 75 MW klystron, designed for low-cost
manufacture, is currently under development at SLAC, and will eventually be
procured from industry in modest quantities for advanced NLC tests. Beyond
these developments, the design of Multiple Beam Klystrons (MBKs) is under study
at SLAC. MBKs offer the possibility of considerably lower modulator costs by
producing comparable power to the klystrons now available, at much lower
voltages.
  * This work supported by the Department of Energy under contract
DE-AC03-76SF00515
