Mode completition and control in high-power gyrotron oscillators

One of the problems in the design of high-power millimeter wave sources such as gyrotron oscillators is insuring that the device operates in the desired mode. For high-power and short-wavelength devices the effective mode density is high, in that the current is above threshold for many modes. One then is led to ask the following questions: Is operation in a single mode possible? What steps must be taken to maximize the electronic efficiency of the device while ensuring single-mode operation? The answer to the first question has been determined to be yes. Provided that certain conditions are met, single-mode operation is stable. However, for a given set of parameters there are many modes that are potentially the stable operating mode. This paper then attempts to address the second question regarding control of the operating mode