A large reduction in the number of klystrons and modulators (4:1, even 6:1) is required to reduce the cost of the Next Generation Linear Collider (NLC). In turn, this will require an equivalent increase in the average power per klystron. Therefore, multiple beam klystrons (MBKs) must be used. This project addresses the solution to the major problem with MBKs, off-axis focusing. In principle, solenoid periodic magnet (SPM) focusing will solve the off-axis focusing problem, while greatly reducing the solenoid power required to focus the beams. Phase I designed a SPM beamstick that is compatible with the SLAC XL4 klystron geometry. The beamstick was fabricated and preliminary tests were carried out, both on and off-axis, in three configurations -- one with the solenoid alone and two with SPM stacks of different periodic length. Whole on-axis focusing was comparable for the three configurations, the SPM configurations required far less solenoid power. Off-axis focusing was far superior with the SPM stacks. In Phase II, two test vehicles will be designed, fabricated and tested in collaboration with SLAC. The first will be a beam tester to establish the entrance conditions and SPM stack parameters for 99% beam transmission. The second will be one module of the MBK, with 12.5 MW peak RF output, 50 dB gain, 250 kV beam voltage and 62 percent efficiency.
Commercial Applications and Other Benefits as described by the awardee: The use of SPM focusing for reduced solenoid power and MBK off-axis focusing should be applicable to any accelerator as well as to high power radars. The savings to the NLC could be as much as $100M.
