Beam positioning and monitoring in the racetrack microtron Eindhoven

A scheme to compensate for the effect of misalignments in the racetrack microtron Eindhoven is presented. An array of small dipole magnets will be employed to obtain closed orbits. These dipoles are located at the symmetry axis of the microtron, in the drift space between the two bending magnets. For each orbit a radial stripline beam position monitor (BPM) will be installed in the field free region. The strength of the corrector dipole magnet in the nth orbit is adjusted with the BPM signal in the (n+1)^th orbit. The design of the BPM´s is described. It will be shown that a rectangular geometry has a distinct advantage over a conventional circular geometry since it is less dependent on vertical displacements of the beam. Expressions for the difference-over-sum signal are given and compared with that for a circular geometry. Results of measurements performed in a test bench on prototype BPM´s are discussed