Key Technologies Of Interaction For High-power Staggered-vane Sheet Beam Traveling-wave Tubes

The vacuum electron device is an ancient yet vibrant technology.The introduction of sheet beam traveling-wave tubes（SB-TWTs）has enriched and expanded the application scenarios of vacuum electron devices.Characteristics such as the ability to carry higher-energy electrons,greater power output,and a lightweight planar focusing system have enabled SB-TWTs to achieve power densities（power output per unit volume）far exceeding traditional TWTs and approaching those of traditional gyro-TWT.This has resulted in significant potential and advantages in fields with stringent requirements for high-power output,power consumption,volume,and weight,such as millimeter-wave communications,synthetic aperture radar,deep-space exploration,and electronic countermeasures.Particularly noteworthy is the high-power output capability in the millimeter-wave and even terahertz frequency ranges,which has become an important distinguishing feature from solid-state devices and photonic devices.The interaction region,which serves as the site for the interaction between high-energy electrons and the electromagnetic field,determines the fundamental energy exchange capability and is the core of TWT design.Among the options,the staggered-vane（SV）interaction structure has become a popular choice for the design of SB-TWTs,thanks to its advantages,such as a transversally expanded interaction region,the high thermal conductivity of the fully metallized structure,the natural SB channel,and the easily integrated planar configuration.However,as SV-SB-TWTs are developed towards higher power,there are still various theoretical and technical bottlenecks,such as power limitations,multi-mode oscillation issues,and efficiency constraints.This series of problems has hindered the development and application of high-power SV-SB-TWTs.In response to the above-mentioned issues,this dissertation conducts theoretical exploration and experimental research from three aspects:fundamental premises,technical implementation,and feasibility requirements.The aim is to provide suggestions and supporting schemes to fully leverage the advantages of SB and achieve high-power output capabilities in SV-SB-TWTs.The main research content is outlined as follows:（1）To address the power limitation of the SV-SB-TWTs in the terahertz（THz）frequency due to the size effect,the dissertation conduct research on the extension limit and feasibility of the high-order mode interaction.The mechanism of terahertz wave amplification is discussed through the interaction between the SB and high-order modes,and a high-order Coalesced-TM₁₁-like mode operation scheme in the SV structure is proposed,exploring the extension limit of the electron channel width.The feasibility of traditional CNC machining techniques and assembly methods for mitigating electromagnetic leakage are also investigated at terahertz frequencies,and a proof-of-concept model verification has been carried out.The results confirm that the high-order mode scheme can broaden the SB width at the same current density to achieve greater current injection,realizing the high-power output capability of SB-TWTs in the THz.（2）To address the insufficient power capacity and heat dissipation capability of SV-SB-TWTs under high-average-power operation in the millimeter-wave（mm Wave）frequency,the dissertation conduct research on the high-frequency system with high-power-capacity SV-SB-TWTs.The electron interception and thermal effect regions are investigated in the SV-SB-TWTs,and based on the advanced microfluidic design concept in integrated circuits,a method to extend the metal vane thickness is proposed to achieve efficient internal heat dissipation and avoid thermal deposition.A trapezoidal SV-SB-TWT interaction structure is developed based on the internal microfluidic design,which realized efficient heat dissipation for the SB-TWTs under high-average-power operation in the mm Wave frequency,and the proof-of-concept verification has been completed.（3）To address the complex issue of potential multi-source oscillation in the SV-SB-TWTs under high voltage and high current working conditions,the dissertation conduct research on mode oscillation and suppression in high-power SB-TWTs.By combining large-signal theory and three-dimensional particle simulation techniques,the self-oscillation risk of the variable-period interaction structure is evaluated by proposing a nonlinear numerical algorithm based on the eigenvalues of the feedback gain to quickly predict the stability threshold of the variable-period interaction section.Compared to the traditional PIC method,this scheme can quickly assess the in-band stability by combining the cold-test results.In the in-depth study of the high-order mode competition problem in the SV-SB-TWTs,the potential oscillation risk of the overlooked high-order Coalesced-TE₂₀-like mode is revealed,and a mode-selective filter weak-coupling loading scheme is designed.The model design and feasibility experimental verification has been completed.The integrated design with the interaction structure effectively avoids post-assembly errors and achieves the filtering of high-order mode oscillation without interfering with the working mode.Finally,the causes and suppression schemes are discussed forπand 2πmode oscillations.（4）To address the technical issues of power and efficiency enhancement in the SV-SB-TWTs,the dissertation conduct research on efficient interaction under full-period velocity and electric field control.The general rule is determined that asynchronous parameters do not affect the extreme efficiency under constant period,and a special periodic distribution form is proposed based on piecewise functions to guide the full-period velocity synchronization technology for rapid optimization of efficiency.The number of optimization variables is reduced to 5,and the algorithm efficiency is improved by an order of magnitude.The process of the interaction is investigated between the SB and the internal electric field in the SV,and the mechanism of the overall efficiency limitation caused by the gain anomaly problem unique to the SB-TWTs is revealed.The use of electric field control technology is proposed to construct a"devil’s horn"electric field to achieve a transversely uniform distribution of interaction strength,which simultaneously increases the single-stage depressed collector efficiency and reduces the size by nearly half.（5）To address the practical issues of large transverse distance,high magnetic field strength requirement,and short transmission distance faced in the design of a focused SB high-frequency system,the dissertation conduct research on the miniaturization technology of a high-frequency system.Leveraging the field compression characteristics of a ridge waveguide,a SB interaction structure design based on a double-ridge waveguide is proposed,which reduces the height of the metal grids and achieves a flattened design.The perturbation mechanism of the side-slot coupling on the sideband modes is investigated,revealing the prominent effect of mode distortion in suppressing upper sideband oscillation.Based on the principle of polarization rotation,a highly compact,high-isolation power coupler design is proposed,which confines the overall coupler size within a wavelength,effectively reducing the risk of electron interception while maintaining high isolation and wideband characteristics and achieving a compact design.