DESIGN AND SIMULATION OF PRACTICAL ALTERNATING-PHASE- FOCUSED (APF) LINACS - SYNTHESIS AND EXTENSION IN TRIBUTE TO PIONEERING RUSSIAN APF RESEARCH

A high fraction of the cost and complexity of conventional linacs lies in the use of magnetic transverse focusing. The strong-focusing effect of alternating patterns (sequences) of gap phases and amplitudes – known as Alternating-Phase-Focusing (APF) – can produce both transverse and longitudinal focusing from the rf field. APF has undeservedly been deemed largely impractical because simple schemes have low acceptances, but sophisticated schemes have produced short sequence APFs with good acceptances and acceleration rates that are now used in a number of practical applications. Suitable sequence design has been difficult, without direct theoretical support, inhibiting APF adoption. By synthesizing reported details and adding new physics and optimization technique, a new, general method for designing practical APF linacs is demonstrated, using simple dynamics and no space charge – incorporation of space-charge and more accurate elements is straight-forward. APF linacs can now be another practical approach in the linac designer’s repertoire. APF 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.