Abstract: A Mobley type bunch compressor is adopted to enhance proton intensity at the Li target hence neutron flux for the Frankfurt Neutron Source at the Stern-Gerlach-Zentrum(FRANZ). At first the micro bunches in one proton macro bunch are successively deflected by a RF chopper located at the front focus of the compressor with various angles, whereafter pass through an optimized magnetic bending system in different trajectories, and finally arrive at the end focus of the compressor, i.e. the target, simultaneously. The chopper cavity consists of a pair of opposite plates serving as a bunch deflector, connected with an inductive winding in series to stimulate resonance at 5 MHz. To design such a chopper, a scaled model is constructed to start with. Theoretical analyses of its RF properties are acc