Study Of Key Techniques On High-power Millimeter Wave Mode Conversion And Transmission

High-power millimeter wave system, mainly consisting of source, mode conversion, mode transmission and radiation subsystems, has been one of the international research focuses for its extensive applications in electron cyclotron resonance heating of plasma, high-resolution radar, directed-energy weapon, and material processing. Within the system, source determines its performance and the other sub-systems such as the mode converter and transition, decide whether sources'efficacy can be exerted effectively. So it is of great significance to study key techniques on high-power millimeter wave mode converter and transition (transmission function).In this dissertation, theoretical and experimental studies of key techniques (conversion or transmission efficiency, band width and compact geometry) on some high power mode converters and transitions operating in millimeter wave band (MWB) are implemented. Furthermore, W band gyrotron also is studied.The study results and work involved are as follows:1. Two kinds of circular mode converters are studied based on the coupled wave theory. One is axisymmetric geometry with periodic perturbations in radius; the other is non-axisymmetric geometry with constant radius and periodically perturbed curvature in one plane. They are able to change respectively azimuthal and radial indices of the circular waveguide modes. Codes to analyze and optimize their geometry are constructed using simplex optimization algorithm. By the codes, TE03-TE02, TE02-TE01 and TE01-TE11mode converters are developed. Cold and hot test experiments involved show good agreements with that from the codes. Moreover, a modified TE01-TE11 mode converter is proposed in order to spread bandwidth of conversion efficiency. Calculations indicate that the modified one exhibits obvious advantages in the conversion efficiency, bandwidth and compact over the original one.2. Numerical calculation codes are written to analyze and optimize waveguide with mutation wall. As an example, optimized parameters of a TE11-HE11 mode converter are obtained by the codes, and the device's power capacity is also estimated for TE11 and TM11 modes, respectively. Cold and hot test results indicate a good agreement with that from codes.3. Operating principle of transition with sinusoidal profile is derived from that of mode converter with axisymmetric geometry and sinusoid-period perturbations on wall. According to the principle, two transitions with sinusoidal profile are proposed. Codes for numerical calculation and optimization of the transitions are constructed. By the codes, optimized structure parameters of the transitons are obtained. Experiments involved are carried out and show good coherence to the calculations.4. Two special transition profiles are put forward to transmit TE01 mode efficiently when spurious modes or even the operation mode is near cutoff. Codes to analyze and optimize them are written. Calculations indicate that these transitions have higher transmission efficiency and are more compact than the available transitions. Experiments show agreements with the calculations.5. Numerical calculation codes are written to analyze Volasov quasi-optical mode converter according to the vector diffraction theory and quasi-optical theory. Calculations instruct that the converter can obtain much better quasi-gauss mode pattern when fed by TE01 mode than the other TE0n modes.6. A code to analyze and optimize gradual complex cavity is written based on the self-consistent nonlinear beam-wave interaction theory. By the code, geometric and electromagnetic parameters of the cavity operating at W-band 2nd-harmonics of TE02-TE03 mode group are obtained. Moreover, particle simulation of the beam-wave interaction in the cavity is implemented to verify the results from the code. Based on the results above, a gyroton with gradual complex cavity is developed. Experiments show that the gyrotron operates at 94GHz and generates 156kW peak power with an efficiency of 27%, which are coherent to the calculations and simulations. Moreover, a set of codes are written to analyze and optimize cavity of a W-band fundamental harmonics monogyrotron based on gyrotron's principle and mode matching method. By the codes, the optimized parameters of the cavity are obtained. Particle simulations manifest that a gyrotron with the cavity may operate at 94GHz, TE03 mode and have a peak power over 127kW with an efficiency of 47%.