Research On Novel Terahertz Sheet Beam Extended Interaction Oscillators

Terahertz technology has made significant progress in recent years,especially in areas such as imaging,communication,and biology.With the promotion and deepening of applications,the demand for high power has gradually become prominent in larger scenarios.Driven by the demand for high-power terahertz source applications,Extended Interaction Devices（EIDs）have been increasingly studied and applied due to their advantages of high frequency,high efficiency,high power,high reliability,low voltage,and miniaturization,making them one of the current research hotspots in terahertz sources.When the frequency increases,there are a series of difficulties in the operation of EID,such as:the skin depth in the terahertz band decreases,and the surface loss caused by the same surface roughness increases sharply;The device size decreases,the electron beam tunnel decreases,and the injectable electron beam current decreases;The reduction of interaction gap can easily cause radio frequency breakdown,etc.These issues will lead to a sharp decrease in EID power,or even no power output.To solve the problem of sharp power decrease in terahertz EID during frequency increase,this paper mainly studies three methods to improve EID power.The first type is EID based on single beam fundamental mode operation,which innovates its structure by increasing the input and interaction area of its single beam,achieving the goal of improving power;The second approach is to optimize the structure of single beam EID,using a combination of sheet beam and high-order mode working mechanisms to make the cavity structure have larger dimensions at the same frequency,overcoming a series of technical difficulties caused by size reduction;The third approach is to interconnect multiple single beam devices and combine multi electron beam technology and power coupling structures to achieve a significant increase in output power.In EID,this paper mainly studies the extended interaction oscillator（EIO）.The main work and innovations of the paper are as follows.1.This dissertation first conducts theoretical research on the sheet beam extended interaction cavity,providing theoretical guidance for the design of subsequent terahertz extended interaction oscillators.In order to improve the power of EIO with single beam fundamental mode operation,a novel two-dimensional slotted structure is proposed.This structure is longitudinally slotted on the transverse grating of the trapezoidal structure,which increases the cross-sectional area of the electron beam tunnel（electron beam current）and the effective interaction area of the electron beam,achieving the goal of improving output power.By studying the influence of longitudinal slotted structural parameters on intrinsic characteristic parameters,high-frequency structures with larger characteristic impedance R/Q and Q₀ were obtained.Afterwards,the two-dimensional slotted structure EIO was validated and analyzed through particle simulation calculations,and the optimal high-frequency structure and output structure parameters were obtained.The working parameters were analyzed,and the following optimal output results were obtained.Under the conditions of effective conductivity of 3×10⁷ S/m,beam voltage of17.2 k V,and current density of 100 A/cm²,the output power is 1878 W,which is more than 21%higher than the optimal output power of the original structure EIO.2.On the basis of theoretical and simulation research on two-dimensional slotted structure EIO,relevant experimental studies were conducted.The results of the cold test experiment are very close to the simulation results,and their deviation is within the allowable range of the design value error.Afterwards,research was conducted on the proposed new terahertz frequency measurement system.The universality of the system was verified through simulation in the W-band and G-band,and the feasibility of the frequency measurement scheme was verified through experiments in the W-band,laying a foundation for subsequent frequency measurement experiments.Prior to the entire tube experiment,a cathode emission test was conducted,and the volt ampere characteristic curves of the cathode were obtained at different cathode temperatures.Finally,the entire tube structure was designed based on a dynamic vacuum system,and preliminary experiments were conducted on the entire tube after processing,welding,and assembly.3.When the frequency continues to increase to the G-band,in order to obtain a larger electron beam tunnel cross-sectional area and cavity power capacity to compensate for the high-frequency losses of terahertz EIO,we continued to study the technology of combining sheet beam and high-order mode working mechanisms that can be applied to terahertz band devices to increase power,and optimized the cavity structure to avoid mode competition,resulting in higher frequency and output power.Research has shown that optimizing the structure can suppress the TM₁₁ mode,which is more conducive to the operation of the TM₃₁ mode,and the optimized structure can feed in larger electron beam power to obtain larger power output.Afterwards,particle simulation verified the improvement of output power and efficiency by optimizing the TM₃₁-2πmode of structural vibration.Under the conditions of effective conductivity of 2×10⁷ S/m,beam voltage of 16.1 k V,and beam current of 0.5 A（current density of 300 A/cm²）,the output power is 130 W and the output wave frequency is 0.22 THz.Finally,cold testing experiments were conducted on the high-frequency structure of the designed high-order mode sheet beam optimized structure EIO,which preliminarily verified the theoretical and simulation design.This research achievement lays the foundation for subsequent research on the novel orthogonal interconnection structure.4.The power improvement of single beam single cavity structure EIO is limited.In order to further improve the power,a novel orthogonal interconnection structure based on the idea of multi beam multi cavity structure is proposed.This structure is horizontally interconnected by four high-order mode single beam trapezoidal structure cavities with the same structural size,which enhances the coupling between the cavities and achieves the goal of significantly improving the output power and efficiency of the device.By comparing and analyzing the intrinsic characteristics of the fundamental mode and various higher-order modes in the structure,the advantages of the interaction between the TM₈₁-2πmode and four sheet beam in the orthogonal interconnection structure were obtained.The particle simulation results show that under the conditions of effective conductivity of 2×10⁷ S/m,beam voltage of 16.6 k V,beam current of 0.77 A（current density of 300 A/cm²）,the output power reaches 503 W,which is 3.9 times the output power of its single beam single cavity structure EIO,and the output wave frequency is0.22 THz.The 3 d B bandwidth is approximately 0.33 GHz,which increases the bandwidth by 57.1%compared to its single beam single cavity structure EIO.Besides,three solutions have been proposed to address the key technical issues related to the formation of four electron beams in the orthogonal interconnection structure EIO:traditional Pierce electron gun,magnetron injection electron gun,and pseudospark electron gun.Finally,cold tests were conducted on the high-frequency structure of the orthogonal interconnection structure EIO to preliminarily verify the simulation results.5.Due to the inability of the single coupling hole output structure to maximize the coupling and extraction of energy within the cavity of the orthogonal interconnection structure,an output coupler adapted to this orthogonal interconnection structure was designed.The simulation results show that,with the beam voltage of 16.7 k V and other operating parameters unchanged,the output power reaches 1056 W,which is 2.1 times the maximum output power of a single coupling hole and 8.1 times the power of a single beam single cavity structure EIO.This output coupler further enhances the output power of the orthogonal interconnection structure EIO.In summary,this paper mainly focuses on the problem of how the vacuum electronic device EIO generates higher power terahertz waves,and conducts progressive and in-depth research layer by layer to gradually increase the power of the devices.The proposed new structures have made a certain contribution to the research of high-power terahertz vacuum radiation sources.