强流质子直线加速器低能输运线束流动力学研究

Beam Dynamics Study on Intense Beam Linac LEBT

  • 摘要: 在低能输运线内,空间电荷、聚焦线圈球差以及束流切割器等引起束流发射度的变大和束流中的 \textH_2^+ 、 \textH_3^+ 等杂质粒子均会增加束流与后续结构的匹配难度,并且为满足实验终端及环形加速器的注入要求,需要将束流切割成不同时间结构。设计低能输运线为双聚焦磁铁结构,并且利用双倾斜极板束流切割器完成脉冲时间结构的切割。优化聚焦磁铁结构,设计带有导向线包的聚焦磁铁以缩短束流输运线长度,降低发射度的增加,并通过动力学模拟计算实现离子源到切割器和RFQ加速器的束流匹配。针对\textH_2^ + 、\textH_3^ + ,根据束流包络设计多级准直结构,降低其在束流中的占比。根据束流动力学设计完成低能输运线束流实验,测试结果表明在传输线出口束流强度为59.6 mA,束流发射度为0.245 mm·mrad,束流纵向切割后可实现400 μs和100 ns等不同脉冲宽度束流。束流强度、发射度和脉冲结构均能满足目标要求。

     

    Abstract: In the low energy beam transport line (LEBT), the increase in beam emittance caused by space charge, spherical aberration of Glaser lens and impurity particles in the beam will increase the difficulty of matching the beam with the subsequent structure. In addition, in order to meet the injection requirements of the experimental terminal and the annular accelerator, the beam needs to be cut into different time structures. The designed LEBT structure consists of dual Glaser, a beam chopper, double beam scraper, and other beam measuring elements. The dual Glaser were used to control the beam transverse parameters to meet the requirements of the RFQ accelerator and the beam chopper for beam emittance and Twiss parameters. The beam chopper is a longitudinal excision of the beam to achieve a different pulse time structure. Finally, the function of the double beam scraper is to control the beam emittance and scrape off the \textH_2^+ , \textH_3^+ impurity particles. Due to the influence of space charge force on the beam, the emittance of low energy intense particle beam increases with the increase of the length of the LEBT. In order to make the LEBT structure more compact, a Glaser lens with a pair of steering coils was developed to simultaneously achieve focusing and offset correction of the beam at the same position. According to the field distribution of the designed Glaser, the beam dynamics simulation software was used to calculate the beam matching from the ion source to the chopper and the RFQ accelerator. The beam chopper adopted the sloped bipole structure, calculated the beam deflection trajectory when the electric field between the poles exists, and optimized the plate structure so that the plate beam loss is zero when the plate high voltage is maximum. Under the same Glaser parameters, the beam envelopes of \textH_^+ , \textH_2^+ and \textH_3^+ were calculated. According to the beam envelopes, a secondary scraper structure was designed between the dual Glasers and before the chopper to scrape off the impurity particles to avoid the influence of impurity particles on the beam transport and acceleration structure. According to the beam dynamics design, the beam experimental research was carried out. The experimental results show that the total beam intensity drawn from the ion source is 84 mA, and the beam intensity is 59.6 mA after collimation scraping in the LEBT outlet vacuum chamber, and the normalized RMS beam emittance is 0.245 mm·mrad using the Allison Scanner. At the same time, the beam chopping experiment was completed, and the longitudinal beam widths after cutting are 400 μs and 100 ns, respectively. The beam intensity and beam emittance can meet the expected requirements.

     

/

返回文章
返回