KARL - a Monte Carlo model for atomic and molecular processes in the tritium atmosphere of the KATRIN experiment

A new parallelized simulation code is presented, which uses a Monte Carlo method to determine particle spectra in the KATRIN source. Reaction chains are generated from the decay of tritium within the source. The code includes all relevant processes: elastic scattering, ionization, excitation (electric, vibrational, rotational), recombination and various clustering processes. The main emphasis of the code is the calculation of particle spectra and particle densities and currents at specific points within the source. It features a new technique to determine these quantities. It also calculates target fields for the interaction of particles with each other as it is needed for recombination processes. The code has been designed for the KATRIN experiment but is easily adaptable for other tritium based experiments like Project 8. Geometry and background tritium gas flow can be given as user input. The code is parallelized using MPI and writes output using HDF5. Input to the simulation is read from a JSON description.本研究提出一种新型并行化模拟代码，该代码采用蒙特卡洛方法（Monte Carlo method）求解卡尔斯鲁厄氚中微子实验（KATRIN）源内的粒子能谱。代码基于源内氚的衰变过程生成反应链，涵盖所有相关物理过程：弹性散射、电离、激发（含电激发、振动激发与转动激发）、复合以及多种团簇形成过程。本代码的核心设计目标为计算源内指定位置处的粒子能谱、粒子数密度与粒子流强，并提出了一种全新的相关物理量求解方法。此外，代码还可计算粒子间相互作用的作用场，以满足复合过程的计算需求。 该代码专为卡尔斯鲁厄氚中微子实验（KATRIN）开发，但可轻松适配诸如Project 8这类其他基于氚的实验。用户可通过输入参数自定义实验几何结构与背景氚气流参数。 本代码采用消息传递接口（MPI，Message Passing Interface）实现并行计算，并以分层数据格式5（HDF5，Hierarchical Data Format 5）写入输出结果。模拟所需的输入参数通过JSON格式的描述文件读取。