Abstract
Summary form only given. The application of chaos in communications and radars offer new and interesting possibilities. We report further investigations on the use of traveling wave tube (TWT) amplifiers as sources of chaotic radiation. Chaos can be generated in a TWT amplifier when it is made to operate in a highly nonlinear regime by recirculating a fraction of the TWT output power back to the input in a delayed feedback configuration. A driver signal provides a constant external force to the system making it behave like a nonlinear forced oscillator, similar to a forced Van der Pols oscillator. In this paper, we describe recent investigations on the effect of a filter in the feedback circuit on the nature and route to chaos. Two different types of filters have been used: (1) a wide pass band and (2) a narrow pass band (NPB). The study illuminates the different transitions to chaos that result from the choice of filter and other parameters such as the driver signal frequency or intensity. To better understand synchronization, an experiment that helps to identify the natural oscillation modes of the system have been carried out by tuning the central frequency of the NPB filter over its bandwidth (with the driver signal put off). Natural oscillation modes were resonantly excited on coincidence with the central frequency of the filter. In experiments using the drive power, the detuning frequency i.e., difference frequency between the driver signal and the natural oscillation of the system was identified as being an important physical parameter for controlling evolution to chaos. Experiments are currently in progress to construct maps that depicts regions of single frequency, self-modulation and chaos and identifies boundaries between them. Finally, a computational model has been developed to simulate the experiments. The simulations confirm that frequency detuning leads to period doubling chaos in conformity to the experiments using the filters.
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