PITZ L波段正导射频光注入器中Cs2Te光电阴极电荷产生的研究
Studies on charge production from Cs2Te photocathodes in the PITZ L-band normal conducting radio frequency photo injector
摘要：
本文讨论了在ps长紫外激光脉冲照射下，L波段正常传导射频腔（RF枪）中Cs_2Te光电阴极产生的电子束团电荷的行为。所产生的电荷在低激光脉冲能量下显示出线性依赖性，正如在量子效率限制的发射机制中所预期的那样，而由于空间电荷限制的发射，观察到其对激光脉冲能量的依赖性对于更高的值要弱得多。然而，直接插入到空间电荷跟踪代码ASTRA的实验参数产生较低的输出电荷在空间电荷有限的制度相比，测量值。在接近空间电荷限制发射机制的高激光脉冲能量下产生的电荷的增加速率似乎与径向激光轮廓中存在的晕圈的量成比例，因为来自芯的电荷已经饱和。通过利用核心+晕粒子分布的基础上测得的径向激光轮廓，ASTRA模拟和半分析的发射模型再现了广泛的RF枪和激光器的测量不确定性的操作参数范围内的测量电荷的行为。
英文摘要：
This paper discusses the behavior of electron bunch charge produced in an L-band normal conducting radio frequency cavity (RF gun) from Cs2Te photocathodes illuminated with ps-long UV laser pulses when the laser transverse distribution consists of a flat-top core with Gaussian-like decaying halo. The produced charge shows a linear dependence at low laser pulse energies as expected in the quantum efficiency limited emission regime, while its dependence on laser pulse energy is observed to be much weaker for higher values, due to space charge limited emission. However, direct plug-in of experimental parameters into the space charge tracking code ASTRA yields lower output charge in the space charge limited regime compared to measured values. The rate of increase of the produced charge at high laser pulse energies close to the space charge limited emission regime seems to be proportional to the amount of halo present in the radial laser profile since the charge from the core has saturated already. By utilizing core + halo particle distributions based on measured radial laser profiles, ASTRA simulations and semi-analytical emission models reproduce the behavior of the measured charge for a wide range of RF gun and laser operational parameters within the measurement uncertainties.
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