External Beam Performance at P.P.A.

The proton beam extraction system which is now operational at the Princeton-Pennsylvania Accelerator is a resonant system operating on the ¿=2/3 radial betatron resonance. This method of extracting from a weak focusing synchrotron was first proposed and shown to work by Turrin et. al. at Frascati, Italy.1,2,3 The system requires that the synchrotron magnet be tuned to ¿r=2/3 with a quadrupole magnetic field component and that an azimuthally varying second harmonic hexapole field be applied to drive the oscillations.4 When the oscillations have reached sufficient amplitude the particles enter the aperture of a septum magnet which bends them clear of the synchrotron. The beam is then steered and focused to the first target point in the External Beam building.