Practical design of alternating-phase-focused linacs
  Conventional magnetic transverse focusing in conventional linear accelerators represents a high fraction of their cost and complexity. Both transverse and longitudinal focusing can be obtained from the radio frequency field by using the technique known as Alternating Phase Focusing. The design of suitable sequences has been difficult, without direct theoretical support, inhibiting Alternating Phase Focusing adoption. Synthesis of reported details and new physics and technique result in a new, general method for designing practical Alternating Phase Focusing linear accelerators. Very long sequences with high energy gain factors are demonstrated, motivated by the desire to accelerate particles over a factor of 500-600 energy gain. The method is demonstrated with simple dynamics and no space charge, later incorporation of space charge and more accurate elements is straight forward. Alternating Phase Focusing can now be another practical approach in the linear accelerator designer repertoire. Alternating Phase Focusing can be used in addition to conventional magnetic focusing, and could be useful in minimizing the amount of additional magnetic focusing needed to handle a desired amount of beam current. 
R. A. Jameson
physics.acc-ph