Transport And Irradiation Characteristics Of Carbon Fiber High Current Pulsed Electron Beam Source

In recent decades,high current pulsed electron beam(HCPEB)has been developed as a technique used for surface modification of materials.HCPEB has the advantages of high energy utilization,clean and small deformation of the treated workpiece,and it has been widely used in industry and aerospace fields.In the electron beam irradiation processing system,the electron beam emission source is one of the most important components.The carbon fiber,which possess low threshold voltage,large emission current density,good emission uniformity and long lifetime,is a perfect material as emission cathode.In this study,planar and annular carbon fiber high current pulsed electron beam sources were designed.In addition,the electron transport and the irradiation process of carbon fiber high current pulsed electron beam source were investigated.Lastly,the irradiation of Ti N coating and 9310 steel were conducted by this carbon fiber high current pulsed electron beam source.The transport process of electron beam emitted from planar carbon fiber high current pulsed electron beam source and the irradiation characteristics were simulated using a Particle-In-Cell and Monte Carlo collisions(PIC-MCC)model.In the process of electron beam transport,the external magnetic field,the irradiation distance and the pressure can influence the trajectory of the electrons as well as the irradiation uniformity.The external magnetic field can restrain the movement trajectory divergence of the electrons in the transport process.When the external magnetic field is 15 mT,the average irradiation current reach the maximum value of 8 kA.The irradiation uniformity of the electron beam on the anode surface is larger than 90%.When the radiation distance and the pressure increase,the collision probability between electrons and neutral particles will raise,which will reduce the number of electrons and current received by the anode.The maximum beam current of the planar carbon fiber high current pulsed electron beam source is about 8k A,and the calculated irradiation energy density is varied from 1.8 to 10 J/cm2.The Ti N coating and the 9310 steel were irradiated by HCPEB emitted from the planar carbon fiber high current pulsed electron beam source.The surface morphology and properties of Ti N coating were obviously changed after electron beam irradiation.The Ti N coating was remelted by the 5J/cm2 electron beam irradiation,and nanohardness of the Ti N coating decreased slightly,while surface roughness increased observably.The bonding strength between Ti N coating and substrate is about 20 N,2 times higher than the untreated coating.When the electron beam irradiation energy density reach 8J/cm2,the resulting Ti N coating shows surface cracks or spalls,indicate that the coating has been ineffective.After the HCPEB irradiation,craters were formed on the irradiated coating surface,which should be the results of the sub-layer melting and eruption through the solid outer surface,as well as escapement of the gas from irradiated coating to atmosphere.After the HCPEB irradiation,craters and surface undulation are clear on the irradiated surface of 9310 steel,and remelted layer has been formed on the top surface of 9310 steel samples.The thickness of the remelted layer increases with the increase of the irradiation energy density.The XRD results indicate that austenite formed in the melted layer.The corrosion resistance of irradiated 9310 steel sample improves greatly in comparison with that of the untreated sample.The transport process of electrons emitted from annular carbon fiber high current pulsed electron beam source and the irradiation characteristics were simulated using a PIC-MCC model.The accelerating voltage,the irradiation distance and the pressure can influence the irradiation uniformity.The larger the irradiation distance and the pressure,the smaller the number of electrons and current received by the anode.The 9310 steel was irradiated by annular high current electron beam.After HCPEB irradiation,a remelted layer was formed on the top surface.The PIC-MCC simulation and experimental results show that the coulomb repulsion between electrons is beneficial for the irradiation uniformity of this annular carbon fiber high current pulsed electron beam source.The irradiation uniformity of the annular carbon fiber high current pulsed electron beam source can be significantly improved using a proper cathode voltage and transport distance.The maximum beam current of the annular carbon fiber high current pulsed electron beam source is about 8k A,and the calculated irradiation energy density varied from 1.4 to 8.3 J/cm2.When the irradiation energy density is about 5J/cm2,the relative standard deviation of the remelted layer thickness of the samples placed at different locations is 9.39%.The result show that the electron beam emitted from annular carbon fiber high current pulsed electron beam source has good practical irradiation uniformity,and can realize the uniform electron beam irradiation for the circular component.