流化固体颗粒靶束靶耦合段中的质子束传输问题研究

The aim of the project is to study the transport of proton beams between proton linear accelerator and granular spallation target. The model of the beam-target coupling used in the project is based on the design of "China Initiative Accelerator Driven System". We use a massively parallel particle-in-cell (PIC) algorithm to simulate the transport of high-intensity proton beams in the coupling section. With the guarantee of large scale simulations, motions of all protons, electrons and ions in plasma, ionization collisions between protons and helium, as well as the evolution of space electromagnetic field are included in our simulations. By performing large amounts of simulations, we are trying to answer the question: (1) the plasma distribution in the whole coupling section, which is caused by the ionization collisions between proton and helium.; (2) the space-charge neutralization of proton beams in low-density plasma, the wakefield effects and self-modulation instability in high-density plasma; (3) the energy loss of proton beams caused by plasma in the coupling section. Beside simulations, experiments will be performed on a low-energy ion-plasma interaction platform. By comparing the experiments and the simulation results ,we are trying to find out on what condition can high-intensity proton beams efficiently transport in coupling section. The results of this project will improve the understanding of the interaction of ion beams with plasma and provide theoretical guild lines for the extensive experimental studies in CIADS.

本课题拟以国家重大科技基础设施“加速器驱动嬗变研究装置”（CIADS）中流态固体颗粒靶束靶耦合段的无窗设计方案为基础，采用基于particle-in-cell 算法的计算机模拟方案，研究颗粒靶耦合段无窗设计方案中氦气碰撞电离后形成的等离子体对束流传输稳定性的问题。它包括：（1）质子束跟氦气碰撞电离，产生等离子体环境；（2）后继束流在低密度等离子体环境中传输时的电荷中和效应，以及在高密度等离子体环境中的尾波场和自调制不稳定性现象；（3）质子束在耦合段复杂等离子体环境中的能损问题。在计算机模拟耦合段的同时，我们也利用合作单位的束流-等离子体作用平台开展先期实验。通过计算机模拟和实验验证，本课题将深入研究耦合段中束流在复杂等离子体和外部磁场环境下的长距离稳定传输问题。

CiADS无窗靶设计方案中，器靶耦合段的束流-等离子体作用过程对束流品质以及散裂靶性能都会产生重要影响。本课题对CiADS无窗靶设计方案中器靶耦合传输段等离子体产生环境进行了详尽论证，分别开发了“CiADS加速器快速模拟软件AVAS”和“束流在等离子体靶中输运算法”两个模拟程序。并据此研究了（1）高能质子束在耦合段中碰撞电离产生等离子体环境的研究；（2）稀薄等离子体中的束流关联效应、自调制现象的叠加、抑制机制，以及磁化等离子体中磁场对自调制现象的抑制效应。（3）稠密等离子体中自生电磁场引起的离子束输运聚焦和扭曲现象，以及非线性能量沉积效应，并在工程物理研究院激光聚变研究中心星光装置和HIRFL 大科学装置上验证了此效应。. 课题对CiADS无窗靶设计方案器靶耦合段等离子体产生环境进行了详尽分析，评估了无窗靶方案中核核反应产生的辐射剂量和安全阈值，给出了评估报告和总体建议，为CiADS进行方案选择提供了理论依据。项目组开发的虚拟加速器模拟软件AVAS，该软件具有高拓展性、高效并行框架、多种核心求解器以及高模块化特征， 是同类加速器模拟软件中速度、精度性能极高的国产软件。通过束流-等离子体靶作用的理论、模拟和实验的比对，课题组实现了强流离子束在大尺度等离子体中的输运过程模拟，发现了自生电磁场引起的离子束输运聚焦和扭曲现象，以及非线性能量沉积效应。本课题课题一方面解决了ciads直线加速器器靶耦合传输段束流传输问题；另一方面深入研究了束流在复杂等离子体靶中的束流输运和能量沉积问题；同时在实验验证过程中，建立了多种束流-等离子体靶实验装置的新方法，完善了相关实验测量和分析。...