Removal of the RF Microstructure from a Proton Linear Accelerator Beam

Abstract

The rf microstructure in the primary proton beam of a proton linear accelerator may consist typically of 0.2ns pulses spaced by 5 ns. This pulsed time structure can be removed to obtain a higher effective duty factor for the proton beam by utilizing the transverse phase space occupied by the beam. An anisochronous beam transport system can produce debunching. One such system consists of a sector magnet with a strong field gradient which bends the beam through 45° and fans it out. A second magnet, of uniform field, bends it through 90°, and a third magnet, identical with the first, recombines the beam and renders it again parallel. The rf microstructure has now been removed, since protons from one side of the beam have travelled ferther than the protons from the other side of the beam. Removal of the rf microstructure in the secondary meson beams could be accomplished with a magnet system similar to but smaller than that for the proton beam. For a sector-focussed cyclotron the above scheme for removing the rf microstructure would require an excessively large magnet system.