| Extended interaction device is one of the linear beam vacuum electron devices by energy exchange between standing wave in extended interaction resonant cavity and electron beam,which includes an extended interaction oscillator and an extended interaction klystron.They are widely applicated in the fields of medical irradiation,radio astronomy,industrial heating and large scientific installations owing to their properties of high power,high efficiency,stability and so on.However,with the rapid development of the science and technology,especially in the applications of the large scientific facilities,including accelerators,colliders,controlled thermonuclear fusion reaction equipment,etc.,which requires the klystrons to be miniaturized,high power and high efficiency.Therefore,this dissertation innovatively combines metamaterials with extended interaction devices,and then carry out the study of theory,simulation and experiment about the metamaterial-inspired extended interaction oscillator(MEIO)and metamaterial-inspired extended interaction klystron(MEIK).The details include:research on the electromagnetic properties of metamaterials;study on the electromagnetic properties of metamaterial extended interaction resonante cavity(MEIRC),and the performance of MEIO and MEIK which use the MEIRC as the interaction structure in achieving miniaturization,high power and high efficiency.The main research contents and innovations of this dissertation are as follows:(1)The electromagnetic properties of metamaterials are investigated theoretically and simulation,and then the corresponding relationships among resonance properties,negative effective electromagnetic parameters,dispersion properties and transmission characteristics of metamaterial slow-wave structure are investigated.Firstly,the expressions of the effective electromagnetic parameters of material under test in different guided wave systems are derived theoretically,and then verified by using normal conventional materials.Based on this,a miniaturized and all-metal metamaterial unit cell is proposed,the effective consititutive parameters,high-frequency properties and transmission properties are studied by using time domain simulation of CST.Furthermore,a miniaturization coefficient is defined to characterize the miniaturization of metamaterials,and then the effects of miniaturization coefficients on dispersion characteristics are studied.It is shown that the miniaturization coefficient along the propagation direction of electromagnetic wave plays a decisive role in the dispersion of the metamaterials slow-wave structure.And the miniaturization coefficient in the vertical propagation direction mainly affects the dispersion passband deviation.(2)The theorey,simulation and experimental studies of metamaterial units filled with hollow circular waveguides are carried out.Especially,the high frequency characteristics of a metamaterial slow-wave structure composed of a circular waveguide loaded complementary electric split ring resonator(Ce SRR)array are studied by using the equivalent circuit method.The influence of structural parameters of Ce SRR element and cavity on high frequency characteristics is analyzed by dispersion equation and coupling impedance equation.On this basis,the experimental study of transmission of metamaterial slow-wave structure is carried out.The simulation and experimental transmission characteristics confirm the transmission passband provided by the negative effective refractive index of metamaterials,that is,the transmission passband operating below the cutoff frequency of the TM01 mode of the circular waveguide.The law of improving the high frequency properties and transmission characteristics of the metamaterials slow-wave structure is investigated.In particular,the main factors affecting the metamaterials slow-wave structure and the electromagnetic characteristics of MEIRC are discussed,which provide a theoretical and experimental basis for the further study of MEIO and MEIK.(3)A design scheme of low voltage MEIO with miniaturization and high electronic efficiency is proposed.The mode distribution of a multigap extended interaction cavity filled with metamaterial units is studied.A compact and low voltage MEIO operating in S-band is proposed based on the normalized electron load conductance and power exchange function.Its transverse and longitudinal dimensions are ?0.2? and ?0.72?(?is corresponding wavelength in free space),respectively.At the same time,a MW-level MEIO in S-band is proposed,and the influence of different gap numbers on MEIO output power is studied.Also,a method of inhibiting electron reflux while improving electronic efficiency is analyzed.Finally,a MEIO operating at 2.866 GHz with an output power of 4.9 MW and an electronic efficiency of 46% is realized,and its transverse and vertical dimensions are 0.35? and 1.71?,respectively.(4)A miniaturized and high electronic efficiency MEIK is proposed by the simulation and cold test experiments.The electromagnetic characteristics of the MEIRC are studied by calculation and simulation,and the potential advantages of MEIRC in terms of structure size and electromagnetic characteristics are analyzed.Furthermore,the cold test experiment of the 2-cavity MEIK was carried out,and the miniaturization characteristics of MEIK were confirmed by experiments.The simulation study of a3-cavity MEIK is further investigated.A saturated output power of 56 k W,an electronic efficiency of 62% and a saturated gain of 47 d B are obtained in the S-band.Finally,the stability of the MEIK,the focused magnetic field and the potential high voltage breakdown risk caused by the miniaturization of the structure are discussed.(5)A kind of miniaturization and high power MEIK for accelerator system are investigated and the corresponding technical scheme are put forward according to the application requirements.The results show that the diameter of the 650 MHz 3-cavity MEIK is about 0.33?,which is about 2/3 of that of conventional counterparts.The saturate output power is 651 k W,the electronic efficiency is 52.8%,and the saturate gain is 35 d B when the length is less than 1.5 m.In addition,a 5-cavity metamaterial-inspired klystron operating at 2.856 GHz with a cavity diameter of 0.33?is studied.Under the conditions of 125 k V beam voltage,beam current of 80 A,focusing magnetic field of 0.2 T and input power of 18 W,the output power is 6.2 MW,the corresponding electronic efficiency exceed 60%,and the saturation gain is 55 d B.Finally,the hot-test experiment of the proposed high-power klystron was carried out.Under the conditions of electron beam voltage and current of 120 k V and 80 A,the output power was greater than 4 MW in the frequency range of 2.852 GHz-2.858 GHz.The maximum output power is 5.51 MW at 2.8523 GHz,the saturation gain is 54.9 d B,and the corresponding electronic efficiency is 57.4%. |
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