Plasma-filled gyro-BWO

Recent theoretical studies have shown that the presence of plasma in the high-power microwave (HPM) sources, when properly introduced, may enhance the efficiency of the source. These findings have been confirmed by numerical simulations for some HPM sources. The enhancement has been partly attributed to the neutralizing effect of the positively charged plasma on lowering the disruptive space charge effects of the electron beam used to generate the radio frequency (RF), and partly attributed to a modification of the dispersion relation leading to higher group velocities for the traveling RF waves. Mode selection may also be favorably affected by the presence of plasma in the source. We present the results of numerical simulations carried out to study the effect of plasma on a gyrotron device. Both neutral as well as positively charged plasmas have been explored. The gyrotron device is run in TE/sub 01/ mode and generates a 12.75-GHz steady oscillation without any competing modes. The effect of the plasma at several different densities has been explored. The presence of plasma at the densities explored do not show any significant enhancement of the gyrotron operation. Other plasma densities are being studied. The particle-in-cell (PIC) code used in simulations was the Mission Research Corporation (MRC) 2.5-dimensional code MAGIC.