| The traveling-wave tube (TWT) has the potential of becoming the RF power source for future linear colliders. Such RF sources require stable amplitude and phase, high peak power ({dollar}>{dollar}100 MW), and high frequency ({dollar}ge{dollar}9 GHz). A previous experiment at Cornell University achieved high power output from a coupled-cavity, TWT with multiple undesirable frequencies. Theoretical analysis shows that these multiple frequencies are caused by positive feedback resulting from reflections at the ends of the device. In this thesis, we present the designing and testing of two TWT devices as the candidates for eliminating positive feedback.; The first device is a severed two-stage TWT device, consisting of a dielectric slow-wave structure as the first stage and a narrow-band coupled-cavity structure as the second stage. The positive feedback in the first stage is suppressed by using distributed attenuation of the EM wave. The second stage has a small wave group velocity (0.008c) to prevent reflections from the output reaching the input within the beam pulse duration. Hence, positive feedback is suppressed by transit time isolation. With a 1 MeV, 1 kA electron beam and 50 kW of RF input power, the two-stage device has been operated with output levels up to 160 MW at 8.87 GHz for the full beam pulse duration of 50 ns.; The other device is a single-stage matched-load device. A 15-period broad-band coupled-cavity structure is matched by a coupler at each end to eliminate positive feedback. In the absence of the beam, the device is matched over two narrow frequency ranges centered around 9.34 GHz and 9.58 GHz. However, in the presence of an electron beam, the device oscillates at current levels as low as 300 A. The oscillation frequencies are located outside of the matched frequency ranges. We were unsuccessful in making the output frequency follow the driving RF frequency. Hence we conclude that the device works as a driven oscillator. This experiment has demonstrated that the key to a successful matched-load TWT device is broad-band matching of the input and output couplers. |
