Advances in plasma-filled microwave sources

Significant improvements in the performance of microwave sources have been achieved in recent years by the introduction of the appropriate amount of plasma into tubes designed to accommodate plasma. Plasma filling has been credited with increasing the electron beam current, bandwidth, efficiency and reducing or eliminating the need for guiding magnetic fields in microwave sources. Neutralization of the e-beam space charge by a plasma enhances the current capability and beam propagation, and the generation of hybrid waves in plasma-filled sources increases the electric field on axis and improves the coupling and efficiency. Control of the plasma density in these microwave sources is often required to avoid instabilities and variations in the output power level and pulse length. Recent experimental and theoretical advances in this field, and the benefits and limitations of plasma filling of several different types of microwave sources, will be discussed.