Multi-mode Self-consistent Non-linear Research On High-power Gyrotron

Gyrotron is a kind of relativistic non-linear device that can generate high power electromagnetic radiation in millimeter wave and terahertz wave.With the rapid development of the magnetic confinement controllable thermonuclear fusion,the requirement for high-power and high frequency microwave sources is increasing in the electron cyclotron wave heating and current drive?ECH&CD?systems of magnetic confinement fusion.Gyrotron has be proven to satisfy their dual-requirements in frequency and power.Especially in the millimeter-wave,the gyrotron has huge advantages in high-power continuous wave operation.Therefore,gyrotrons have been used in many currently operating thermonuclear fusion reactors to provide the high-power millimeter-wave source.With the further increase in the requirements of power and frequency,the gyrotron has to operate at high-order volume mode to maintain reasonable cavity transverse dimensions at the operating frequency and then to improve the power capacity.However,gyrotron operating at the high-order volume mode will bring a serious mode competition problem in the cavity.That is an important factor to influence the normal operation of the high-power gyrotron.Therefore,the research on this kind of problem is very important and necessary.At same time,in high-power gyrotron?especially in megawatt-level gyrotrons?,the ohmic wall losses of the cavity also needs special consideration.The effect of cavity thermal deformation on beam-wave interaction caused by ohmic wall losses cannot be ignored.Under the supported by the sub-project“long pulse high power gyrotron key technology research”of National key research and development plan intergovernmental international scientific and technological innovation cooperation special magnetic confinement fusion energy development research project,the topic of this thesis mainly focuses on the study and analysis of non-linear multi-mode beam-wave interaction in the cavity of high-power gyrotron.The main contents of this thesis are as follows:1.Base on the time-dependent self-consistent beam-wave interaction model,transmission line equation,and electron motion equations,a numerical simulation code has been developed for studying multi-mode beam-wave interaction,which has been demonstrated by comparison with CST and EURIDICE developed by KIT.2.A 95 GHz,400 kW class gyrotron has been designed.The gyrotron works in the high-order volume mode TE_22.6.Using the developed code,a detailed multi-mode beam-wave interaction nonlinear analysis was performed,and the influence of the quality of the electron beam?beam thickness and velocity spread?on the beam-wave interaction was simulated and analyzed.Finally,the gyrotron was assembled,vacuum processed,and tested.Under test conditions with a voltage of 51.6 kV?pulse width of 30 us?,a current of 24 A,and a magnetic field of 3.615T,the output power of 435 kW with the operation frequency of 95.21 GHz are obtained.3.For studying the ohmic losses problem of the high-frequency cavity of high-power gyrotron,the multi-physics analyses in electromagnetics,thermodynamics,and structural mechanics have been proposed.The cavity system of the 140 GHz,MW-class gyrotron developed by our group has been studied in detail.The cavity of the gyrotron operates at high-order volume mode TE_28.8.In the analysis,the effects of thermal deformation of the cavity on cold-cavity characteristics and multi-mode beam-wave interactions under different cooling conditions have been analyzed in detail.4.Based on the requirements of DEMOnstration fusion reactor for multi-frequency high-power gyrotrons,a MW-class gyrotron working at 210-240-270 GHz has been researched and designed.In the studies,the selection method of operating mode group of this type of gyrotron has been proposed in detail.Finally,the mode group with TE_-35.15-TE_-40.17-TE_-45.19 modes is selected as the operating modes for the corresponding operating frequencies at 210 GHz,240 GHz,and 270 GHz,respectively.Based on the linear analysis,the non-linear multi-mode self-consistent time-dependent beam-wave interaction analysis is performed for each operating mode at correspongding operating freqeuncy,in which the electron parameter controlled by a triode magnetron injection gun is considered in the startup scenario process.In the non-linear analyses,the time-dependent multi-mode beam-wave interaction processes for each main operating frequency are studied with considering ideal and non-ideal electron beams,respectively.