Numerical Simulation Study Of MW-level Inductively Coupled Plasma Generator

In order to study the "radio blackout" problem in the aerospace field,different types and levels of plasma wind tunnels have been established around the world,such as shock wind tunnel,arc plasma wind tunnel,inductively coupled plasma wind tunnel(also known as radio frequency plasma wind tunnel)and so on.In order to explore the interaction mechanism between high-speed target plasma and electromagnetic waves,inductively coupled plasma discharge is applied to a major national scientific research instrument development project led by Xidian University.The device produces a plasma flow with the typical characteristics of a hypersonic vehicle plasma sheath-wide parameter range,high collision frequency,nonuniform,high dynamic plasma flow.It provides a dedicated ground experimental platform for conducting reliable communication research under high-speed target plasma environment.Plasma generation is a complex process.It is completed by the coordination of multiple subsystems such as intake,ionization,vacuum,and cooling.In order to achieve the typical characteristics of the plasma sheath,the MW-level inductively coupled plasma(Inductively Coupled Plasma,ICP)discharge method with higher electron density is adopted by this device.The MW-level plasma generator is a key component of the inductively coupled plasma generation and control system.On the one hand,the characteristics of the plasma generated in the quartz tube directly affect the state of the plasma jet in the vacuum chamber.On the other hand,the quartz tube is the weakest part of the entire device.The temperature of the inductively coupled plasma with high power can reach tens of thousands of K,which is easy to cause thermal damage such as cracking and softening of the quartz tube.Therefore,it is necessary to conduct a detailed study on the discharge characteristics of the inductively coupled plasma and the temperature of the quartz tube.In this thesis,the characteristics of inductively coupled plasma discharge under high power,large size,and radio frequency medium pressure are analyzed from both numerical simulation and experimental aspects.The main work is summarized as follows:(1)The COMSOL multi-physics simulation software is used to study the related physical characteristics of the discharge of the inductively coupled plasma generator under high power,large size(length 815 mm,diameter 180mm),and radio frequency(440k Hz)medium pressure(1000Pa).The discharge characteristics of inductively coupled plasma in different parameters such as power,mass flow,and air pressure are obtained.Considering the complex physical environment of the MW-level inductively coupled plasma generator,the theory of magnetohydrodynamics is introduced.Then the multi-physics coupling process of electromagnetic field,temperature field and turbulence field is studied.Due to the general room temperature boundary conditions of the quartz tube cannot reflect the real situation of the experiment,thinking the boundary conditions and initial conditions that are closer to the real experimental situation,the surface radiation to the environment and the convective heat flux boundary of the cold air blowing on the wall are simultaneously set on the outer wall of the quartz tube.The influence of different coil power,inlet mass flow and gas pressure on the spatial distribution of plasma is explored.Under different working conditions,the distribution law of the electromagnetic field,temperature,joule heat,wall temperature,velocity and other parameters of the plasma inside the generator and the physical mechanism of formation are analyzed.And the temperature of the quartz tube of the generator is estimated,which can be applied to engineering temperature resistance evaluation.(2)The analysis of the discharge image and spectrum diagnosis of the MW-level inductively coupled plasma generator are carried out.The results show that the temperature measured by the experiment is close to the numerical simulation result,and the change trend distribution of them is also more consistent.It not only verifies the validity of the numerical simulation,but also gains a more detailed understanding of the discharge characteristics of inductively coupled plasma,and analyzes the cause of the circular discharge distribution.The main reasons are the rotating intake and skin effect of the induced current.(3)A three-dimensional plasma model is established,and the two-dimensional model is optimized and improved.The rotating intake and turbulent flow are considered comprehensively,and the effect of the special intake method—rotating intake on the plasma heat transfer and flow characteristic is explored.It is found that the flow has a relatively high velocity near the inlet and the inner wall of the quartz tube in the area where the coil section is located,especially in the upstream of the first turn of the coil,there is an unstable flow around it,the flow will cause rupture and damage to the quartz tube wall.Through experimental analysis and numerical simulation,the influence of factors such as working parameters and inlet method on the characteristics of plasma discharge and the temperature distribution of the quartz tube wall are studied.And through the verification of spectral diagnosis and the analysis of the discharge image,the validity of the numerical simulation is demonstrated.These works not only provide theoretical support for the engineering evaluation of the temperature resistance of quartz tubes,but also provide basic theoretical data for the optimal design of the inductively coupled plasma wind tunnel and its industrial applications.