高压直流连续波光阴极注入器中电子束流发射度研究

Study on beam quality of CW photoinjector based DC gun

高平均功率自由电子激光研究中,电子束质量是关键。针对高平均功率自由电子激光目标参数,提出了直流高压连续波光阴极注入器,给出了注入器的束流动力学过程。为了降低输出束流横向发射度,采用特殊结构设计的静电加速腔,加速电压1MV,最大加速梯度10MV/m。用PARMELA程序进行了粒子动力学模拟,电子束束团电荷为0.5nC,束团长度10ps时,注入器输出束流归一化发射度均方根值为5.8mm·mrad。

Electron beam quality is very important in the highaveragepower FEL. According to the characters of CAEP highaveragepower FEL, CW Photoinjector Based DC Gun is proposed in the paper. The beam emittance growth is also investigated under the condition that the beam distribution on the cathode is of Gauss's distribution. The beam emittance growth is mainly due to the space charge effect when the electron beam is accelerated and drifts after acceleration, so the field strength and the voltage are both very important to the injector. With the novel structure of the electrostatic acceleration, the field strength is more than 10MV/m, and the voltage is more than 1MV. After the beam simulation by PARMELA code, 5mm.mrad of the normalized beam emittance (rms) is acquired when the beam charge is 0.5nC and pulse duration (rms) 3ps.