| Due to the characteristics of high power, high efficiency, stable frequency andphase, the relativistic klystron amplifier has been proved to be one of the promisingcandidates for the high-power microwave coherent power combining. However, therelativistic amplifier devices always require the external injection source to supply tensof or hundreds of kilo-watts power. It means that RF power up to10MW is needed forlocking dozens of amplifiers. This is beyond the output capacity of the external sourcewhich is, commonly, a commercial magnetron of MW levels, particularly as attemptingto scale the system to the higher operation frequency. One potential solution for thisissue is employing a high power external source of GW-class to replace the commercialmagnetron. Because of the plenteous output power of the external source, there is nolimitation on increasing the number of the amplifiers.In this dissertation, the mentioned idea is preliminarily validated at a relativelylower frequency by using an S-band relativistic backward wave oscillator (RBWO) asan external source to drive a high power injection two-cavity wide-gap klystronamplifier (WKA) for frequency and phase locking. The related theoretical analyses, PICsimulations and initial experiments are carried out on such a RBWO-WKA system. Thedetailed contents and main conclusions are presented as following.In part one, influences of the washers/rods structure of the WKA on the highfrequency characteristics and the basic operation of the amplifier are investigated. Theanalyses show that the return current rods play the more important role in depressing thespace-charge potential of the wide-gap cavity than the metallic washers. Once the rodsare employed, the potential effect can be greatly suppressed even a fewer of washers areused. Moreover, only if the wide-gap cavities are properly tuned, influences of the rodsize on the basic operation of the WKA, such as the beam current modulation and theRF power extraction, are believed to be very weak.In part two, to further understand the essential operation process of the WKA underthe high power inspiring case, the external RF signal injection and beam currentbunching are inspected. The impedance matching condition between the electron beamand the external load is obtained according to the circuit model. Considering theelectron bunching theory and the PIC simulation results together, the formationmechanism of the second peak current in the case of high voltage modulationcoefficient is discussed. The results indicate that the second peak current has a closerelation with the electron multiple-overtaking phenomenon.In part three, the two-cavity WKA with high power injection is researched in detailthrough the three dimensions electromagnetic particle-in-cell (PIC) code. Basing on theoptimized configuration, the WKA output power of about1.5GW with the conversion efficiency of36%and power gain of14.6dB is achieved under diode voltage of595kV,beam current of4.9kA, input power of36MW and working frequency of3.6GHz.Furthermore, dependences and sensitivities of the output power on the diode voltage,the injection power and frequency of the RBWO source are attained. Benefited from thehigh power injection condition and the two-cavity structure, affects of the injectionpower and frequency on the WKA output power are alleviated. The phase locking effectof the WKA with regard to the diode voltage is also discussed. It demonstrates thatoutput frequency of the WKA is linearly locked by the input frequency of the RBWO.However, for practical application in a power combining system, frequency and phaselocking are supposed to be satisfied simultaneously. In order to restrict the phasedifference of the two-cavity WKA within a narrow enough range, the external RBWOsource should have good frequency reproducibility and stability from pulse to pulse. Itrequires excellent voltage stability in the experiment.In part four, the initial experimental studies on the two-cavity WKA driven by theRBWO are accomplished. Preparations of the dual-beam accelerator, the dual-cathodediode, the RBWO external source, the solenoid of the WKA and the time-delay triggersystem are introduced. Under the injection power of~22.5MW, injection frequency of3.55GHz, diode voltage of530kV, beam current of4.1kA and confinementmagnetic-field of1.6T, the WKA output power is about229MW with RF pulse widthof70ns, conversion efficiency of10.9%and power gain of about10dB. Theseexperimental results are compared with that of the PIC simulation cases. Moreover, theperformance of the triggered gas-gap switch of the accelerator is examined and theinfluence of the diode voltage on the phase-locking effect of the RBWO-WKA systemis observed. While the gas-gap switch is externally triggered, the diode voltage and theinjection frequency from the RBWO are maintained around530kV and3.55GHzrespectively within a series of shots. Phase difference between the external source andthe two-cavity amplifier is less than±16°in a single shot, and phase jitter within±11°isgained from shot to shot, with locking duration of about40ns. |
PDF Full Text Request