| As one of the types of millimeter wave radiation sources,vacuum electronic radiation sources(VERS)have been widely used in aerospace and military science and many other aspects due to their absolute advantages of high operating frequency and high power,and are still being widely studied and developed.However,with the increase of the operating frequency,the size of the high frequency(HF)circuit of the VERS will also decrease,and this small-sized HF circuit greatly limits the further development of millimeter wave VEDs.Firstly,the thermionic cathode of the traditional VERS needs to be heated to a high temperature,while the small-sized HF circuit is difficult to withstand such a high temperature directly,so it is necessary to use various means for heat insulation,resulting in a large volume and weight of the device;secondly,the risk of breakdown caused by the gap voltage of the small-size circuit is greatly increased.Meanwhile,the use of high operating voltage makes the device difficult to miniaturize;Finally,The small-sized beam tunnel increases the design difficulty of the electronic optical system of the device.The carbon nanotubes(CNTs)cold cathode can work at room temperature and easy to transplant,it can effectively avoid the problems caused by high-temperature operation in traditional thermionic cathode VERS.Therefore,in order to solve the technical difficulties faced by the development of millimeter VERS,in this dissertation,three key technologies,namely the CNTs electronic optics system,mechanism of low operating voltage millimeter wave VERS and the large-sized beam tunnel HF structure,are studied.CNTs cold cathode electronic optics system was studied.Adopting planar planted CNTs with a radius of 1 mm as the electron source,a planar emission CNTs cold cathode electronic optics system is proposed.The experimental results indicate that the total emission current of the CNTs cold cathode can reach 92 m A,the emission current density is up to 2.93 A/cm~2,and the beam transparency of the electronic optics system is77.9%.On the basis of the above research,a large-area planted CNTs are used as the electron source,a dual-gridded CNTs cold cathode electronic optics system is designed,and the shadow grid directly covering in the CNTs effectively solved the problem of electron interception by the grid.The experimental results show that when the surface electric field intensity is 8.86 k V/mm,the emitting current of the diode is 1.02 A,the corresponding emitting current density is 768 m A/cm~2,and the stability and life test results show that the cathode performs well.The triode test results indicate that the electron transparency of the dual-gridded CNTs cold cathode electronic optics system is up to～100%,and the electron spot observed at the exit position of the anode channel presents a regular circular shape and uniform brightness,and its diameter is 3 mm,which is consistent with the simulation results,the maximum current density of the electron beam formed after compression is about 10 A/cm~2,and the current density is uniform.The low voltage millimeter wave VERS is studied.Based on the theory of nano-cold-cathode field emission,a working mechanism is proposed,without the intervention of external HF signals,the CNTs cold cathode field emission can be directly modulated by the HF field excited in the HF structure.Different from the electronic velocity pre-modulation in traditional devices,the pre-modulation method in this dissertation is to modulate the process of electron emission,and the density-modulated electron beam emitted from the cathode latterly interacts with the HF field in the HF structure,dramatically improving the beam wave interaction efficiency.Applying the above working mechanism to backward wave oscillator(BWO),a low voltage,140 GHz CNTs cold cathode BWO is designed,The particle in cell(PIC)simulation results indicate that under the conditions of low voltage of 2.9 k V and initial current of 15.8 m A,the emitting current modulation depth reaches 443%,the device is capable of output power of 4.6 W,and the efficiency reaches 10%.Furthermore,using the planar planted CNTs with a radius of 1 mm as the electron source,a Ka-band pre-modulated BWO is designed,the PIC simulation results indicate that the output power is 91 W,the frequency is 32.8 GHz,and the efficiency is 6.7%.The millimeter wave HF structure of large-sized beam tunnel are studied.A circular beam wave interaction structure with coupling hole is proposed,this structure can focus the HF electric field towards the center,so that the HF electric field component in the beam tunnel can be enhanced,and sufficient beam wave interaction can be ensured in the large-sized beam tunnel device.In G-band,a three-coupling hole extended interaction cavity is designed and optimized,the diameter of the beam tunnel is 0.26 mm,and compared with the general device,the beam tunnel diameter is increased by 40%.The PIC simulation results of the four cavities extended interaction klystron(EIK)indicate that the device is capable of a maximum output power of 134.5W,and has a 3-d B bandwidth that reaches 1 GHz,the corresponding gain is 30.3 d B and the efficiency is 4.6%.furthermore,based on the dual-gridded CNTs cold cathode electronic optics system,the Ka-band CNTs cold cathode EIK is designed and optimized,with a diameter of 2.2 mm,the extended interaction cavities of the three-coupling hole structure are fabricated and cold test experiments are carried out,and the experimental results are basically in agreement with the simulation,which verifies the feasibility of such a large-sized beam tunnel HF structure. |
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