Study Of Tin Oxide Impedance Wall Materials And Their Application In Travelling Wave Amplifiers

Travelling wave amplifiers amplify high frequency signals by the interaction between the electron beam and the high frequency electromagnetic field.Much clustered the electron beam is,the more energy it gives to the electromagnetic field.Conventional travelling wave amplifiers rely on the circuit field to cluster the electron beam.In the impedance wall travelling wave amplifier,the surface plasma wave generated by the impedance wall will enable further clustered of electron beam.Less research has been done on impedance wall travelling wave amplifiers and their amplification potential is yet to be investigated.For impedance wall travelling wave amplifiers,the electrical properties of the impedance wall material mainly determine the small-signal gain,and tin oxide has proven to be a reliable impedance wall material.As a result,the small-signal gain of its travelling wave amplifiers can be investigated by studying the electrical properties of tin oxides impedance wall material.In this thesis,the properties of tin oxides impedance wall material are investigated by first-principle calculation,and the small-signal gain of its impedance wall travelling wave amplifiers is investigated.The main work and results of this thesis are as follows:（1）First-principle calculations are carried out for SnO₂and SnO.The calculation theory,pseudopotentials,exchange-correlation functionals and software package are selected for this research,and first-principle calculation studies are carried out for SnO₂and SnO,in which the crystal structures,band structures,electron effective masses and dielectric properties of SnO₂ and SnO are obtained.The electron relaxation frequency of SnO₂ is obtained based on the electron-phonon matrix calculation.The electrical conductivity of SnO₂ is further obtained based on the Drude model.（2）First-principle calculations on the SnO₂ oxygen-vacancy model and the model of SnO₂ with extra electrons are carried out.With the oxygen-vacancy in SnO₂ and the influence of beam electrons on the properties of the impedance wall material considered,the SnO₂ oxygen-vacancy model and the model of SnO₂ with extra electrons are created,and studied by first-principle calculation.The crystal structures,band structures,electron effective masses and dielectric properties of them are obtained.The electron relaxation frequency of the model of SnO₂ with extra electrons is calculated by electron-phonon matrix calculation,and the conductivity is obtained based on the Drude model.（3）The small-signal gain of tin oxide impedance wall travelling wave amplifier is investigated.Based on the conductivities of tin oxides,the small-signal gains of tin oxides impedance wall travelling wave amplifiers are calculated.The results indicate that the operating conditions,structural parameters and material properties will affect the small-signal gain.With higher current densities,lower operating voltages,thinner support material or support material with lower dielectric constants used,the small-signal gain of impedance wall travelling wave amplifier will improve.