Absolute instability enhancement for a plasma filled rippled wall rectangular waveguide backward wave oscillator driven by sheet electron beam

Summary form only given. A linear theory is presented for generation of high power microwaves (HPM) through backward wave oscillator (BWO) driven by a sheet electron beam in plasma filled rippled wall rectangular waveguide as a slow wave structure. By matching the boundary conditions at the junction of beam edge, plasma, and metallic boundary the dispersion relation and the growth rate (temporal and spatial) have been derived numerically. While analysis, we have used sheet beam of 6 kA at 250 kV with transverse cross section of about 0.5 cm by 2 cm and relativistic factor gamma /spl gamma/=1.5 this beam is currently operational at D.A. University Indore. To see the effect of plasma on the TM/sub 01/ cold wave structure mode and on the generated frequency, the parameters used are average waveguide height a=1.5 cm axial corrugation period z/sub g/=1.67 cm and corrugation amplitude h=0.225 cm. The plasma density is varied from 0.0-8/spl times/10/sup 19/ cm/sup -3/. The presence of plasma tends to raise the TM/sub 01/ mode cutoff frequency (10 GHz at plasma density 8/spl times/10/sup 15/ cm/sup -3/) relative to the vacuum cutoff frequency (5 GHz) while also causing a decrease in the group velocity everywhere, resulting in a flattening of the dispersion relation. With the introduction of plasma an enhancement in spatial and temporal growth was observed.