These devices have obvious applications for tactical HPM. Shorter-wav moderate-power source also have a number of defense applications, such as radar and space communication. A convenient, tunable source at the shorter-wavelength end of the millimeter-infrared region of the spectrum has a broad range of applications in basic research and applied technology.91 16908oneway of improving the output power capabilities of ultra-high-power microwave radiation sources is through the use of highly overmoded resonant structures. Experiments performed in the soviet union on the relativistic Multiwave Cerenkov Generator (MWCG) have demonstrated output power of > 10 gw at frequencies of 10 ghz with conversion efficiencies close to 50% . We propose to theoretically model the beam-wave interaction in the MWCG using weakly-irregular waveguide theory. This will produce a nonlinear self-consistent field multimode theory of the device. The theory will be evaluated numerically assuming only one mode is present in the interaction region. We will then use the theory to aid in the design a highly overmoded MWCG experiment to be performed in phase n. A successful development of the MWCG would produce an ultra-high power centimeter or millimeter wavelength radiation source. MWCG's could be developed for advanced directed energy weapons and for systems vulnerability assessment. The MWCG could also be used commercially as a source for high power radar applications and as a power source in advanced accelerator designs.