热阴极径向温度非均匀性对本征发射度的影响

从热发射理论出发，推导了非均匀发射阴极的均方根本征发射度的一般计算形式。针对一种最常见的温度径向分布近似模型，给出了均方根发射度随温度非均匀性变化趋势的理论数值解。基于有限差分法粒子仿真技术统计了热阴极的本征发射度，仿真结果与理论解一致，验证了非均匀发射热阴极本征均方根发射度一般形式的正确性。结果表明，径向温度非均匀性引起均方根发射度显著变化，非均匀系数为10%时引起均方根发射度下降约15%。本文建立的理论形式和仿真方法可以有效评估束流品质控制目标和工程热设计之间的依赖关系，以指导高效费比的工程设计。

Intrinsic emittance of thermal cathode with radial temperature variation

Thermionic cathode is widely used in accelerators, FELs and all kinds of vacuum electronics. For better performance and long stable running, low emittance with notable contribution from cathode is needed. Emittance of perfect thermal cathode only depends on radius and temperature. However, emission non-uniformity exists due to cathode surface profile, material distribution, temperature variation, crystal orientation, etc., which may cause intrinsic emittance growth, brightness decline, envelop size augment, device performance deterioration or even failure. To understand how intrinsic emittance is manipulated by temperature variation, a general intrinsic emittance model consisting of contributions from surface non-uniformity is developed based on general thermal emission. Numerical calculation for a cathode with radial temperature variation shows that RMS emittance declines about 15% when non-uniformity reaches 10%, which well conforms to FDTD-PIC simulation result.