An ionization profile monitor can collect either ions or electrons produced from residual gas ionization. A magnetic field can be used to confine the drift path of the electrons, reducing distortion introduced into the clearing electric field by the beam space charge. We have designed, built, measured, and installed in the Fermilab Main Injector a permanent magnet for this purpose. We discuss the requirements for such a magnet, especially the effect of magnetic strength and imperfections on the measured electron profiles, and the performance of the magnet as built.
