Development of grid-controlled electron gun for Rhodotron
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摘要: 花瓣型加速器是一种具有结构紧凑、高效率特点的加速器装置，其运行依赖一种高重复频率、短脉冲且低发射度的电子枪，以确保最佳的加速性能。据此展示了该类电子枪的物理设计、模拟仿真、样机研制和束流测试情况。该电子枪设计为一种基于钡钨热阴极的栅控电子枪，采用皮尔斯结构，其阴极电压-40 kV，工作重复频率为10.75 MHz，设计的最大发射电流可达200 mA，单个脉冲最小长度不超过3 ns。实际测试中，该电子枪在阴极热子工作参数0.95 A/6.7 V，加载阴极直流电压-40 kV，栅控电压290 V/10 MHz时，测得峰值发射电流为204 mA。当束流脉冲长度底宽2.7 ns时，束流幅值为39.2 mA，还测试得到实际束流发射度＜2 mm·mrad，满足设计和加速器应用需求。Abstract: The Rhodotron is a compact and highly efficient accelerator. This accelerator requires an electron gun with high repetition frequency, short pulses and low emittance, to ensure optimal acceleration performance. This paper shows the physical design, simulation, prototype development and beam testing of such an electron gun. The electron gun is designed as a grid-controlled electron gun based on a barium-tungsten thermionic cathode. The electron gun adopts a Pierce structure. It has a cathode voltage -40 kV, an operating repetition frequency of 10.75 MHz, a design emission current of 200 mA maximum, and a single minimum pulse length of 3 ns. In the actual test, the electron gun measured a peak emission current of 204 mA with the cathode heater operating at 0.95 A/6.7 V, loaded cathode DC voltage -40 kV, and gate control voltage 290 V/10 MHz. When the beam pulse length is 2.7 ns, the beam current amplitude is 39.2 mA, and the actual beam emittance is less than 2 mm mrad. This result meets the design and accelerator application requirements.
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Key words:
- Rhodotron /
- electron gun /
- grid-controlled /
- thermionic cathode /
- beam test /
- emittance
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图 2 用EGUN程序计算出的电子枪束流轨迹(40 kV/200 mA)
Figure 2. Beam optics in the gun calculated with the EGUN program
图 3 CST程序中电子枪三维模型仿真结果汇总
Figure 3. Summary of simulation results of the 3D model of the electron gun in the CST program
图 6 电子枪工作在202.4 mA峰值束流时的示波器测试信号
Figure 6. Oscilloscope test current signal with the gun running at 202.4 mA peak beam current
图 7 电子枪工作在2.7 ns束流脉宽时的示波器测试信号
Figure 7. Oscilloscope test current signal with the gun running at 2.7 ns beam pulse width
图 8 电子枪正常工作时各参数间关系的测试结果
Figure 8. Test results of the relationship between parameters during normal operation of the gun
图 9 多缝法测量发射度原理图
Figure 9. Schematic diagram of emittance measurement by multi-slit method
图 10 发射度测试中焦斑经过狭缝后的图像及其对应曲线
Figure 10. Image of the focal spot after passing through the slit in the emittance test and the curve corresponding to the image
表 1 电子枪参数
Table 1. Electron gun parameters
type max beam
current/mAanode
voltage/kVheater
voltage/Vheater
current/Agrid
bias/Vmin bunch
length/nsbeam emittance/
(mm·mrad)Max repetition
rate/MHztriode 200 40 8 1.05 400 3 ≤2 10.75/107.5 
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