Preparation And Properties Of Diamond Films On Plasma-Facing Components Surface Based On Novel MPCVD Device

At present,controlled thermonuclear fusion energy is considered to be a clean energy that can effectively solve the future energy needs of mankind.Combustion plasma,Tokamak fusion reactor engineering technology,and various materials of fusion reactors are the three major factors that affect the industrialization of Tokamak fusion reactors.In magnetic confinement thermonuclear fusion device,the surface materials of plasma-facing component will interact with plasma and enter plasma to form impurities,whose radiation has an important impact on the stable operation of the high-parameter plasma.In the early stage,most of the medium and large Tokamak experimental devices basically used carbon block as the first wall and the surface material of the divertor target plate.In the future Tokamak fusion reactor,the high tritium retention characteristics of carbon blocks will affect the system safety of fusion reactor.Tungsten has the characteristics of high melting point,good thermal conductivity,high sputtering energy threshold,and low tritium retention rate.So it is considered to be the ideal plasma-facing materials for future Tokamak fusion reactors.But tungsten is also a high atomic number material(Z=74),less tolerant in fusion plasmas.When it enters the fusion plasma,it will produce a large loss of energy radiation,reduce the heating efficiency and energy confinement,and in severe cases will leads to plasma rupture.As a carbon material,diamond is the hardest material in the world.In addition it has the characteristics of low physical sputtering rate,strong chemical inertness and excellent thermal performance.Diamond films is deposited on the surface of tungsten material approved by Tokamak fusion reactor as the plasma-facing materials,and its thickness is about one tenth of that of carbon watt.It is expected to improve the tolerance of fusion plasma to impurities and reduce tritium retention while meeting the performance requirements of Tokamak fusion reactor engineering materials.As plasma-facing materials of the Tokamak fusion reactor,the tungsten-copper mono-block is the divertor target plate component to withstand the maximum plasma heat flow.In this paper,the surface(facing the plasma)of the tungsten-copper mono-block is used as substrate,the microwave plasma chemical vapor deposition(MPCVD)device is used to study the physics of low-temperature plasma and prepare diamond films.The main work and innovations of the paper are as follows:(1)In view of the defects of plasma-facing materials selection(tungsten,graphite,Carbon Fiber Composite(CFC))in the application of magnetic confinement thermonuclear fusion devices,this paper proposes to prepare diamond/tungsten composite materials on the surface of tungsten substrate for application in plasma-facing materials.(2)According to the size of the Mono-block tungsten block,a new quartz tube MPCVD resonator was used to prepare the diamond/tungsten composite material,and studied the effect of adding the resonator to the upper substrate stage on the electric field strength and plasma physical parameters.Compared with the traditional quartz tube MPCVD resonator,the finite element simulation results by COMSOL Multiphysics show that the electric field and plasma electron density in the optimized new resonator are more concentrated in the middle region of the two substrate,with higher intensity.Optical emission spectroscopy(OES)diagnostic results show that the new resonator has a higher and more concentrated group density in the hydrogen plasma,which is lower than that of the conventional resonator at the edge of the plasma discharge.The comprehensive results show that the addition of the upper substrate stage can make the plasma discharge area more concentrated and centripetal,which has a favorable impact on the protection of the quartz cover,and provides a new platform support for safe,efficient and long-term preparation of diamond/tungsten on the surface of Mono-block component.(3)The stress and shear force of diamond/tungsten composites were studied by ANSYS workbench finite element simulation and experimental characterization.With the increase of diamond films thickness,the maximum principal stress and maximum shear stress of the whole diamond films show a trend of decreasing first and then increasing.The lowest value is at the films thickness 75-100μm.At the same time,the stress increases at the edges and corners of the films,which is prone to cracking.Through Raman characterization and comparison of the prepared samples,it is found that the diamond films with 103.56 μm thickness has the smallest total stress,which Provides a stress basis for surface application of plasma-facing components in Tokamak devices.(4)On the premise of not introducing other element impurities,the transition layer from particle blasting and gradient blasting are proposed for the first time to improve the adhesion between films and substrate.Firstly,WC particles carry out sandblasting on the tungsten surface of tungsten-copper mono-block,resulting in irregular dents and pits on the surface,and significantly roughness increasing.Some WC particles have been embedded in the rough surface,which plays a bonding role in the transition from tungsten substrate to diamond carbon material,and the adhesion between films and substrate is also improved accordingly.On the basis of WC particle blasting,we continue to use diamond micro powder for blasting.The blasting treatment of diamond micro powder will reduce the roughness of the original WC particle blasting surface.However,the diamond deposition changed from heteroepitaxial to homoepitaxial growth,which will promote the adhesion between diamond films and tungsten substrate.(5)The properties of the samples for future fusion were preliminarily tested for the application of diamond/tungsten composites in fusion devices.The hydrogen permeation and retention behaviors of diamond/tungsten composites were tested by electrochemical hydrogen permeation and Thermal Desorption Spectroscopy(TDS).The results show that the hydrogen permeability and retention of diamond films are slightly higher than that of tungsten materials,and much lower than that of graphite materials.Graphite,tungsten and diamond were irradiated by deuterium plasma.After irradiation,large-area sputtering appeared on the surface of graphite;Small cracks and pits appeared on the surface of tungsten material after irradiation,but the whole remains intact;As an allotrope of graphite,diamond shows partial graphitization after irradiation,and there is no sign of sputtering on the surface.The prepared diamond/W composites were subjected to high heat load fatigue test.After 50 times electron beam irradiation cycles at 6.3 MW/m2,the diamond films did not peel and fracture.