Experimental And Theoretical Study On ICP For B₄C Coating Fabrication

The magnetic confinement fusion energy,which is achieved through magnetically constrained thermonuclear fusion with hydrogen isotopes that of inexhaustible in the sea water,is considered to be the ultimate clean energy source available for human.We are working towards this goal.One of the important topics of fusion research is the new material closely related to the plasma energy constraints and particle constraints,such as the plasma facing materials(PFMs).PFMs are the materials used in plasma facing components such as first wall,deflector and limiter in fusion devices.At present,tungsten(W)material is considered to be the preferred PFM material for future fusion reactors for its high melting point and good thermal conductivity.However,one of the core issues to be solved in the magnetically constrained thermonuclear fusion for high atomic number(Z)value of W(Z=74)is the serious radiation loss of plasma energy,which can greatly reduce the heating efficiency and energy constraint time.This is because bremsstrahlung power density caused by electron-ion collision in plasma is proportional to Z2.In addition,the high Z tungsten material would induce the instability of electrical resistance(such as resistive tearing mode instability).This is because the resistivity of plasma is directly proportional to Z,the added W undoubtedly would greatly increase the resistivity of the plasma compared with that Z=1 fusion material(deuterium-tritium).The first wall material is required not only to be with good thermal and mechanical properties,but also to have the ability to reduce recirculation of the impurity especially for the heavy impurities(high Z element)effectively when the plasma interacts with it.As a consequence,the first wall material has become the overcoming difficulties subject research in the field of ftision.At present,the composite material of B4C/W,with low Z value refractory boron carbide(B4C)coating deposited on the W material that with good thermodynamic performance and low recirculation of heavy impurities propertities,has attracted high attention from the international ftision area and become the focus research of fusion area.Currently,the preparation methods of B4C/W include chemical vapor deposition,borylation and magnetron sputtering.But high efficiency preparation techniques or methods for B4C coating deposited on W substrate which with high hardness and melting point are rarely seen in the world and are still blank in China.Therefore,research on the preparation of B4C/W coating by radio frequency(RF)inductively coupled plasma(ICP)spraying was carried out in this study.And the platform to test technical feasibility of the plasma first wall material of B4CAV coating prepared by RF ICP spraying was established.The reason why we use ICP torch instead of DC plasma torch is that ICP torch has no electrode ablation pollution and the powder can be effectively melted compared with DC plasma torch.As a pioneering experimental study of a new technical route,the main purpose of this study is to establish a research platform for preparation of B4CAV coating with a certain bonding strength,and to verify the technical feasibility of this technical.Also this can provide a basic achievement for further research.to take into account the advantages of high temperature of torch that,can effectively melt B4C powder to improve the adhesion force of coating and the advantages of fast coating speed,and to get rid of the disadvantages of impurity pollution caused by electrode ablation of dc torch and improve the purity of B4C coating.It is of practical significance and practical value for the research of the first wall material of controlled thermonuclear fusion.The main work and innovations of this paper are as follows:1.Theoretical numerical simulation of ICP temperature field,velocity field and conductivity distribution was done for physical design of the experimental platform,providing theoretical basis for the engineering design of the experimental platform.2.A pair of voltage and current probes was installed for diagnosis of voltage and current on the RF transmission line of the ICP torch for the examination of the relevance of technical parameters and RF coupling of the research platform.It provides a new way for ICP diagnosis,as well as the parameter influence for the B4C coating experiment,determination of the controllable range of engineering parameters in accordance with the B4C coating.3.The experimental research on the preparation of ICP spraying B4C/W coating was carried out.Experimental physical conditions(such as spray distance,gas flow rate,input power,substrate material and temperature)for coating bonding strength were optimized.Morphology,phase and composition of the coating were characterized.13.1 MPa bonding strength of the B4CAV coating was prepared.The scientific feasibility of ICP spraying of B4C/W coating,and the technical feasibility of the experimental research platform have been fully proved.