Designs of the low energy intertank quadrupole magnets for APT

The 700-MHz room temperature Low Energy (LE) Linac for the Accelerator Production of Tritium (APT) facility employs three different types of coupled cavity drift tube linac (CCDTL) structures to accelerate a 100 mA CW proton beam from 6.7 MeV to 96.9 MeV and two different types of side coupled cavity linac (CCL) structures to accelerate the beam from 96.7 MeV to 211 MeV. Focusing of the beam is done with quadrupole electromagnets located between the segments of the accelerating structures in a FODO lattice. Since the longitudinal space available for the magnets is severely limited, the ratio of the magnet core length to the bore diameter varies over the range from 0.9 to 1.4. The pole tips have been designed with 3-D finite element modeling to keep total field harmonics less than 1% of the quadrupole component within 3/4 of the beam tube aperture. In this paper, we present the physics parameters, detailed design, and some magnetic measurements of the prototypes for the two of the quadrupole magnet designs.