| Relativistic backward-wave oscillator(RBWO)is considered to be one of the most promising high-power microwave sources,for its high output power,high conversion efficiency and high repetition rate.Output pulse energy of RBWO is a key parameter which is severely limited by intense radiation frequency(RF)breakdown.In the pursuit of higher power,the attainable power level and pusle width of the RBWO will inevitably decrease due to the RF breakdown,which greatly retards its application.In this work,based on the physical process of the anode breakdown model,we carried out studies of the electron beam bombardment on metal materials.The main results are as follows:(1)In the article,the energy deposition of ~Me V electrons in metal materials was studied using Bethe energy loss law and Monte Carlo simulation.The results indicated that,electrons in the material of smaller atomic number and density had much longer effective range and the energy deposition density was lower.Thereby,the material was more resistance to electrons bombardment and the breakdown risk could be effectively reduced.According to erosion threshold of metals,the principles to choose an optimal material were obtained: low density,high melting point,large specific heat capacity.(2)With the same incident electron energy,the copper,stainless steel and titanium were experimentally compared.Owing to its high density,low melting point,and small specific heat capacity,the copper was destroyed more easily.Simultaneously,the titanium showed good performance for its low density,high melting point,and high specific heat capacity.The principles to choose an optimal material for RBWO have been verified preliminarily.(3)The CST simulation was used to design a waveguide resonator with strong field side of 1.8 MV/cm.The field distribution on both sides of cavity was asymmetric.The electron emission and bombardment properties of materials were studied separately to clear the anode mechanism caused by strong electromagnetic field vacuum breakdown.Under a guided magnetic field of 1 T,the stainless steel waveguide resonator with strong electromagnetic field vacuum breakdown,could reduce pulse width from 25.2 ns to 15.6 ns,reduced by about 38%;and reduce output power from 2.06 GW to 1.78 GW,reduced by about 13.6%.Compared to stainless steel,using the electron-resistant bombardment of titanium material could increase the pulse width about 3.8 ns,and increase the output power about 0.14 GW.(4)Under a guided magnetic field of 1 T,compared with stainless steel,TC18 with the best performance could increase the pulse width from 15.6 ns to 24.8 ns,and increase the output power from 1.78 GW to 2.04 GW.The experimental results showed that the titanium material was more resistant to electron beam bombardment,it could relieve the pulse width reduction and power drop by strong electromagnetic field vacuum breakdown.The excellent performance may be due to the small grain size of ? phase,which can strengthen the crystal structure and delay the nycleation of crack,which can increase the beam bombardment performance;and the emission performance has also improved.Based on theoretical analysis and numerical calculation,the optimization principles of materials resistant to electron bombardment in strong field environment have been obtained.The related research results can provide support for the material optimization in RBWO and simultaneously guidance for the theoretical studies of the strong electromagnetic field vacuum breakdown. |
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