Base line design for the Intense Microwave Prototype wiggler

We describe the base line design for the wiggler to be used in conjunction with the Experimental Test Accelerator‐II (ETA‐II) to produce high‐power microwave radiation in the Intense Microwave Prototype (IMP) free‐electron laser experiment. This design produces negligible noise growth for spontaneous noise sources as large as 20 dB above shot noise, and thus corrects the defects present in earlier iterations of the design, which resulted in diminished gain at the signal frequency because of space‐charge effects as well as enhanced spontaneous noise growth at frequencies lower than the signal frequency. In addition, more realistic engineering design constraints on the waveguide size and the wiggler gap spacing have been set by the waveguide wall loading and the electron beam fill factor and have been incorporated in the final base line design. The design assumes that the ETA‐II accelerator will supply an electron beam with an energy of 10 MeV, a current of 3 kA, and a brightness of 1.0×108 A/(m rad)2. With...