基于束流环形高斯模型对上海硬X射线自由电子激光装置的束流刮束器进行活化分析

Analysis of radiation protection for beam collimator at SHINE facility

在建的上海硬X射线自由电子激光装置(Shanghai HIgh repetition rate XFEL aNd Extreme light facility,SHINE)的加速器隧道内,采用束流刮束器刮掉束晕外围张角比较大的电子,刮束器的束流损失率为0.1‰。本文采用蒙特卡洛程序FLUKA,用SOURCE程序实现电子束在3σbeam外的高斯分布,以尽量真实模拟电子在束流刮束器处的丢失情况,解决了低功率刮束情况下蒙特卡洛模拟无统计性结果的难题。利用束流环形高斯模型对刮束器的活化进行了分析,结果表明环形高斯模型可以更真实地再现电子在束流刮束器的丢失情况;5年运行后距刮束器30 cm处的剩余剂量率达到了数百μSv/h至数mSv/h,和国外类似装置计算结果相当;通过对放射性核素的种类分析,结果证明刮束器(钨)的放射性废物处置难度不大。

The Shanghai HIgh repetition rate XFEL aNd Extreme light facility(SHINE)under construction is located at Zhangjiang Hi-Tech Park,Shanghai.The SHINE facility consists of an 8 GeV continuous-wave(CW)superconducting linear accelerator,a 100 PW laser system,three undulator lines,and ten experimental end-stations at phase-I.The SHINE facility will be built in a tunnel 29 meters underground,with a total length of 3 km.In the tunnel of No.2 shaft,there are many beam collimators for scraping off electrons with a relatively large opening angle at the periphery of the beam halo,and the beam loss rate of the beam collimator is 1/10,000.In this paper,the Monte Carlo program FLUKA is used to simulate the Gaussian distribution of the electron beam outside 3σbeam with its SOURCE program.The model to simulate the loss of electrons at the beam collimator is called the beam ring-type Gaussian model.The main material of the beam collimator adopts tungsten to attenuate the strong radiation caused by the electron electromagnetic shower.The model was used to analyze the activation of the beam collimator.The results show that the Gaussian distribution model can more realistically reproduce the loss of electrons in the beam collimator.Gaussian distribution model was used to analyze the activation and the results prove that the disposal of tungsten radioactive waste is not difficult.