Orbit-reversing magnets for the National Bureau of Standards-Los Alamos Racetrack Microtron

In the National Bureau of Standards (NBS)-Los Alamos Racetrack Microtron (RTM), the 17-MeV electron beam that has made one pass through the RTM linac is deflected 180 degrees in one end magnet and is returned to the same end of the (standing wave) linac for a second pass. A pair of dipole magnets on the linac axis compensates for the beam displacement caused by the end magnet, so that the beam enters the linac on axis. The two magnets are designed to have equal field integrals in order to produce a pure displacement. Matching the field integrals was complicated by the quite different widths of the two magnets, which have different beam clearance requirements. In addition, the wider magnet contains a quadrupole coil for beam steering. Design considerations for the magnet system are presented. Magnetic field measurements show that critical design goals have been achieved.