Design and analysis of D2 gas target for high-current linear accelerator neutron source
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摘要: 中子转换靶是强流直线加速器中子源的重要组成部分，在强流粒子束（质子或氘离子等）的轰击下，中子转换靶的散热是当前制约中子产额提升的关键因素，具有强散热能力的高性能气体靶是其中的解决方案之一。针对传统气体靶散热能力不足的问题，通过对靶室结构的改进，设计了一种新型动态气体靶系统。开展了气体靶系统和靶室结构的概念设计，并利用Target软件计算了气体靶金属窗和气体体靶对入射离子的能量歧离效应，结果显示：因气体造成的能量歧离很小，金属窗是入射离子能量歧离的主要来源。通过耦合SRIM计算加热功率，实现了热源随气体密度的动态加载，模拟了不同流强和不同入口速度条件下靶室内气流流动规律，结果表明，随着流强增加，加热功率逐渐升高，加热区密度迅速下降，同时提高靶室入口速度能够增强散热能力，减小因束流加热引起的密度下降效应。最后对气体靶产生中子的整体性能进行了评估，计算了不同流强下的中子产额及其能谱分布，当流强为10 mA时，气体靶的中子产额可以达到5.2×1012 n/s。Abstract:
Background Neutron nuclear data are crucial for fundamental research in nuclear physics, providing essential information for nuclear science and engineering applications. Advanced high-current accelerator neutron sources serve as the foundation for nuclear data measurements. The neutron converter target is a key component of such high-current accelerator neutron sources. Under intense particle beam bombardment, the heat dissipation of the neutron converter target is a critical factor limiting the neutron yield and operational stability.Purpose This study aims to address the insufficient heat dissipation capacity of traditional gas targets by designing a novel dynamic gas target system. By optimizing the structure of the gas target chamber to form an active cooling circulation loop, it seeks to solve the cooling problem within the confined space of the gas target chamber.Methods First, a conceptual design of the gas target system and chamber structure was conducted. The Target software was then used to analyze the energy straggling of incident ions caused by the metal window and the gas itself. Numerical simulations of the thermal environment inside the gas target chamber were performed. The heat source was dynamically loaded based on gas density by coupling with SRIM calculations of the heating power. The gas flow patterns within the target chamber under different beam currents and inlet velocities were analyzed.Results The energy straggling calculations show that the contribution from the gas is very small, with the metal window being the primary source of energy straggling for incident ions. The simulation results indicate that as the beam current increases, the heating power rises gradually, while the density in the heated region decreases rapidly. Increasing the inlet flow velocity enhances the heat dissipation capacity and reduces the density drop effect caused by beam heating.Conclusions The comprehensive performance evaluation demonstrates that this dynamic gas target system can achieve a neutron yield of up to 5.2×1012 n/s at a beam current of 10 mA. The results prove that the novel dynamic gas target system effectively improves heat dissipation performance, contributes to obtaining a higher neutron yield, and ensures operational stability under high-current application scenarios.-
Key words:
- neutron source /
- gas target /
- energy straggling /
- numerical simulation /
- neutron yield
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图 5 入射离子能量歧离
$ {E}_{\mathrm{s}\mathrm{t}\mathrm{r}} $ 随钼窗厚度的变化Figure 5. The variation of energy straggling with the window thickness
图 6 钼窗中能量歧离随入射离子能量E的变化
Figure 6. The variation of energy straggling with the incident ion energy
图 7 氘气中入射离子能量歧离
$ {E}_{\mathrm{s}\mathrm{t}\mathrm{r}} $ 的概率密度Figure 7. The PDF of energy straggling of incident ions in deuterium gas
图 8 氘气中能量歧离随入射离子能量E的变化
Figure 8. The variation curve of energy straggling with incident ion energy
图 11 靶室中速度、压力、温度和密度分布
Figure 11. The distribution of velocity, pressure, temperature and density in the target chamber
图 12 靶室中心流线上温度和密度分布
Figure 12. Temperature and density distribution on the central streamline of the target chamber
图 14 靶室中心x=0 m位置处温度和密度剖面
Figure 14. Temperature and density profiles at x = 0 m in the center of the target chamber
图 15 靶室中心加热功率和平均密度随束流流强的变化
Figure 15. Variation of heat power and mean density of target chamber center with beam current intensity
图 16 气体靶中子辐射场计算构型
Figure 16. Computational configuration of neutron radiation field of the gas target
表 1 靶室入口流动参数设置
Table 1. Inlet flow parameter settings of the target chamber
No. velocity density pressure temperature current case1 10 m/s 0.982 kg/m3 202650 Pa100 K 10 mA case2 20 m/s 0.982 kg/m3 202650 Pa100 K 10 mA case3 20 m/s 0.982 kg/m3 202650 Pa100 K 1-10 mA 
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表 2 出射中子能量及其半高宽
Table 2. Emitted neutron energy and its FWHM
incident
deuteron
beam
energy/MeVoutgoing
primary
neutron
energy/MeVFWHM
of the
neutron
energy/MeVenergy
spread of
the outgoing
neutron10 12.7 0.158 1.24% 11 13.67 0.152 1.11% 12 14.63 0.139 0.95% 13 15.59 0.134 0.86% 14 16.55 0.125 0.76% 15 17.51 0.121 0.69%
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