Gyrotron operation in the 'no-start-current' zone

It is conventionally assumed that the gyrotrons can operate either in the regime of soft self-excitation, where the beam current exceeds the start current, or in the regime of hard excitation, where the beam current is lower than the start current. The authors have found one more possibility of gyrotron operation: in the region where there is no start current at all. Although it is not clear whether this region represents a special interest for gyrotron operation, it can be useful to learn that such opportunity may exist and can be used for interpreting some experimental results.