Design of a 2.5 MeV miniaturization accelerator with high average beam power based on dielectric materials
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摘要: 横向尾场导致的束流崩溃效应是限制加速器向强流小型化发展的主要因素。介质金属盘片混合加速结构是具有小型化高束流功率特性的新型加速结构，但其结构较为复杂，导致装配和调谐困难。通过开展介质金属盘片混合加速结构研究，明确介质材料对腔体性能的影响，从而优化结构以解决装配和调谐的问题。该结构优化后可以大幅度降低横向尾场导致的束流崩溃，增大束流功率。基于优化后的结构，设计一只工作频率为S波段
2856 MHz，具有小型化高束流平均功率特性的2.5 MeV加速管。介绍了加速结构的优化及加速管的物理设计，采用数值计算方法完成了加速管束流动力学设计，并用PARMELA进行了验证计算。本研究明确该结构具有成为新一代大束流功率辐照直线加速器的潜力。-
关键词:
- 加速器 /
- 介质金属盘片混合加速结构 /
- 尾场 /
- 束流崩溃
Abstract: Industrial linear accelerators are gradually moving towards high average beam power in small, compact shapes. The beam break-up effect due to the transverse wakefield is the main limitation to its performance improvement. The hybrid dielectric-iris-loaded structure is a new miniaturization accelerating structure with high average beam power. The main problem is difficulty in assembly and tuning. Through the study of dielectric based accelerating structures, a miniaturization accelerator with high average beam power was designed and optimized. During the research process, the influence of dielectric structural parameters on the accelerating structure size, accelerating gradient, and beam power was analyzed. The optimized accelerating structure size was reduced by about one-third compared to conventional iris-loaded accelerating structure. It can achieve the same acceleration gradient. The insertion of a simple dielectric tube into the dielectric structure made assembly and tuning easier. The optimized accelerator operats at S-band with the frequency of2856 MHz and voltage of 2.5 MeV. During the research process, beam dynamics is calculated through numerical calculation methods and PARMELA. Our research provides an important groundwork for further development of irradiation linear accelerators. -
图 2 盘荷波导以及介质金属盘片混合加速的结构对比及参数
Figure 2. Comparison between a conventional iris-loaded accelerating structure and a hybrid dielectric-iris-loaded accelerating structure
图 3 优化后的介质金属盘片混合加速结构
Figure 3. Optimized hybrid dielectric-iris-loaded accelerating structure
图 10 加速管出口处束流束斑与能量分布
Figure 10. Beam size and energy distribution at the end of the linac
表 1 盘荷波导与介质金属盘片混合加速结构的结构参数对照
Table 1. Comparison of structural parameters between the disk-loaded accelerating structure and the hybrid dielectric-iris-loaded accelerating structure
structure L/mm a/mm g/mm b/mm h/mm ht/mm disk-loaded accelerating structure 34.99 10.75 19.99 41.1 − − hybrid dielectric-iris-loaded accelerating structure 34.99 10.75 19.99 31.35 20 5 
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表 2 盘荷波导与介质金属盘片混合加速结构的微波参数对照
Table 2. Comparison of microwave parameters between the disk-loaded accelerating structure and the hybrid dielectric-iris-loaded accelerating structure
structure f/MHz R/Q of TM01 Q vg/c R/Q of HEM11 disk-loaded accelerating structure 2856 4656 14096 0.0115 4300 hybrid dielectric-iris-loaded accelerating structure 2856 2626 7140 0.0061 2067
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表 3 加速管主要设计参数和运行参数指标
Table 3. Design and operation parameters of the linac
f/MHz Ein/keV εrms/(μm·rad) Pin/MW Eoutput/MeV $ {\bar {{P}}}_{\mathrm{I}} $/kW Ib/mA duty factor/% 2856 50 2.5 3.5 2.5 16 800 0.8
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表 4 加速管各单腔参数
Table 4. single cavity parameters of linac
cavity βg cavity number L/mm a/mm g/mm h/mm ht/mm Q R/(MΩ/m) vg bunch cavity 1 0.5 2 17.5 10.75 12.5 20 5 4000 5 0.0048 bunch cavity 2 0.7 2 24.5 10.75 19.5 20 5 5800 10 0.0057 accelerating cavity 1 11 35 10.75 30 20 5 7140 17 0.0061
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