DESIGN OF THE PROTOTYPE NUMI PROFILE MONITOR SEM

The NuMI primary proton beam profile will be monitored by a series of secondary emission monitors (SEM's). The present note describes the design of a SEM which implements 5µm Ti foils, segmented for X and Y readout, moving on a sliding "gate-valve"-like frame. The foil-supporting frame remains out of the beam during insertion and removal of the device, permitting insertion without stoppage of the beam. A prototype detector has been assembled for testing in the MiniBoone 8 GeV transfer line.