Dielectric loaded CARM

Summary form only given. A cyclotron autoresonance maser (CARM) with a dielectric loaded waveguide structure to allow low-voltage operation has been developed. For the initial experiment, a 75-kV, 4-A electron beam with α=0.6-1.5 was employed to interact with a wave near the light line. To optimize the interactions in both the wiggler region and the CARM region, the axial solenoid field in each region was controlled independently. By sweeping the axial magnetic field of the CARM solenoid and hence moving the cyclotron resonance line along the dispersion curve of the wave; several axial modes in the cavity were excited, including a gyro-BWO (backward wave oscillation). A wave with large k_||≈ 0.7 (ω/c) was excited at 12.72 GHz with a Doppler upshift of 44%, albeit at a power of only 300 W. The electron beam´s velocity spread inhibits the generation of waves with large k_||. To enhance the interaction efficiency and to excite the desired wave with k _||≈ω/c, the period of the wiggler has been doubled to reduce the axial velocity spread from 8% to less than 2%