Technical innovations for a high-gradient quadrupole electromagnet intended for high power proton drift tube linacs

The IPHI project includes a 352 MHz drift tube linac (DTL) to accelerate a 100 mA cw proton beam from 5 to 10 MeV (1 MW beam power). The main challenge of such a structure is to house a strong gradient quadrupole (QP) in the very reduced space of the first drift tubes (DT). Having chosen not to use permanent magnets, the goal is to design 4.70 T integrated-gradient QP less than 50 mm long with 90 mm maximum outer radius and an aperture as large as possible to minimize beam losses. Two DT have been designed and built with different QP magnets for the low energy end of the IPHI DTL. The first one is based on conventional magnets with hollow conductors and high-permeability cobalt-iron alloy for the poles and yoke. Two separate cooling circuits are used for the DT and the magnet coils. A second design has been done to make profit of the full space available inside the DT and to reduce their manufacturing cost as much as possible. A single water flow is used to cool simultaneously both DT body and QP coils made up of full (nonhollow) conductors.