直流光阴极注入器电子束壁损失初步研究

Preliminary study of electron beam wall loss in photocathode DC injectors

真空度被认为是影响GaAs阴极寿命的最重要参数之一,电子束在阴极附近的壁损失会导致真空度下降。基于高斯分布模型,研究了中国工程物理研究院自由电子激光相干强太赫兹源(FEL-THz)直流光阴极注入器电子束在束线管壁上的损失情况。通过理论分析、数值计算、束流动力学模拟、热力学分析及电子束初步出束实验研究,证明了FEL-THz电子束壁损失能达到W量级,必然引起真空度下降和阴极寿命缩短,这是目前限制出束的重要原因之一。研究表明,为维持电子束持续稳定工作,应将注入器阳极后的管道尺寸扩大到至少45mm。

Ultra-high vacuum （UHV） has been demonstrated as the most important condition for long lifetime GaAs photo cathode.To create the UHV environment and extend the GaAs lifetime,the electron beam wall loss in DC injectors is studied in this paper.A DC injector is installed in free electron laser THz （FEL-THz） facility in CAEP.The study is based on Gaussian distribution model.With theoretical analysis,numerical calculation,dynamic simulation,thermal simulation and prototype experiment discussion,this beam loss is proved to be a few watts,indicating that it is the main reason for vacuum and quantum efficiency loss,which will dramatically decline the beam-out time.Furthermore,the study also indicates that the diameter of the tube after the anode should be at least 45 mm.