Stabilizing plasma-filled microwave tubes

Summary form only given, as follows. Plasma-filled microwave tubes have several advantages over conventional vacuum filled tubes. For example, the plasma neutralizes space-charge, allowing higher current to flow. Also, the phase velocity of electromagnetic waves in a plasma is higher than in vacuum, allowing higher frequencies to be produced from a tube of a given size. Unfortunately, the microwave generation process couples to the ion motion, causing ion density fluctuations that in turn cause fluctuations in output frequency and power. We have found how to prevent these fluctuations from growing to unmanageable size. The basic principle is to continually replace the plasma ions in the microwave interaction region in a time short, or comparable to, the time of growth of the ion plasma instabilities. As an example, we demonstrate a gas-filled orbitron maser that operates at constant frequency in the state. In this device, an intense radial field ejects ions in a time sufficiently short to damp growing plasma ion instabilities. In addition, several other experiments will be discussed in which the ion instabilities have been suppressed. Also, mathematical modeling of this stabilizing process will be presented.