Investigation Of An X-Band New Coaxial High Power Microwave Source Based On Dual Beams

Limited by the material technology and physical mechanism, a single high power microwave(HPM) source has a finite power handling capacity. What's more, the rising electron beam current is prone to surpass the space charge limiting current, which will lead to the decrease of beam-wave conversion efficiency and constrain the input electric power. In order to solve problems aforementioned, based on the survey of dual-band high power microwave sources, an X-band new coaxial high power microwave source based on dual beams is proposed, and the frequency and phase locking between inner and outer sub-sources is realized. Furthermore, a microwave of higher power is obtained through power combination of two phase-locked microwave beams, whose frequencies are identical and relative phase remains stable. This new device has several advantages. First of all, the dual beams make a larger total current, which leads to a smaller corresponding impedance and is beneficial for acquiring a higher input electric power. Meanwhile, each sub-source can operate in relatively low current and high impedance, which is favorable for the high conversion efficiency of each sub-source, and it is not easy for each one to surpass the space charge limiting current. Then, power combination makes a relatively low power in each sub-source possible, which reduces the probability of the internal radio-frequency(RF) breakdown. In summary, the proposed device is promising for low-impedance, high-level output power, high efficiency and long-pulse operation and miniaturization. The main content is as follows.Firstly, the inner and outer sub-sources are designed and simulated separately, and their operation frequencies are optimized to be almost identical. Besides, the feasibility of the two sub-sources co-operating under the low magnetic field is analyzed.Secondly, the frequency and phase locking between the two sub-sources is investigated. Particle-in-cell(PIC) simulations demonstrate that, a microwave with a power of 1.3GW and a frequency of 9.74 GHz is generated by the inner sub-source when the diode voltage is 674 k V, the guiding magnetic field 0.8T and the inner electron beam current 6.6k A; the corresponding efficiency is 29%. Meanwhile, a microwave of the same frequency with a power of 2.5GW is generated by the outer sub-source, and the beam current is 14.3k A, with the efficiency of 26%. The relative phase between the two output microwaves levels off at 83° with a fluctuation of around ±5°. When the diode voltage shifts from 675 k V to 755 k V, the relative phase changes about 18°, which is advantageous for the power combination.Thirdly, power combination of this new device is studied. The combination effect of the combiner is validated in the diode voltage range from 675 k V to 755 k V as well as in the pulse regime. The simulations indicate that, when the diode voltage is 675 k V, a combined microwave with an average power of 4.0GW is generated; corresponding to a total efficiency of 29%, and the maximum surface axial electric field strength locates at the downstream end of the second SWS of the inner sub-source, approaching 720 k V/cm, indicating that the power handling capacity is relatively high.Finally, some engineering structures related to the presented device, including magnetic field coils, a mode converter and supporting bars are designed. In addition, in order to measure the output of each sub-source individually in experiments, two absorbers are investigated preliminarily.