核设施退役过程中的辐射场重构与拆除路径优化

辐射场分布和路径选择是核设施退役过程中影响工作人员吸收剂量的主要因素。针对核设施退役过程中多源项的三维辐射场,采用点核积分的方法进行重构,重构结果与蒙特卡罗程序计算结果吻合很好,验证了点核积分法的可行性。将核退役拆除路径问题抽象为一种类旅行商问题数学模型,构造不同拆除路径下所受外照射剂量对应的剂量矩阵,根据辐射防护ALARA(As Low As Reasonably Achievable)原则,利用遗传算法进行寻优。对于多源项退役拆除实例,计算给出了最优化拆除路径和三维可视化显示,并对优化效果进行了讨论。设计开发了面向核设施退役过程的辐射场重构与拆除路径优化功能软件。     

Experimental study of double tearing mode on EAST tokamak

The double tearing mode(DTM)in a high βN(βN>1.5)discharge with internal transport barrier on EAST was investigated.A 15 kHz tearing mode(TM)(m≥3,n=3)appears at outer q=2 surface at first,which is stable in the highβN phase.Then a 2 kHz TM(m=2,n=1)occurs at inner q=2 surface.Soon after,high βN collapsed with the crash of ELM,and DTM formed during the collapse of βN.The positions of the two islands of the DTM are consistent with the q=2 surface.The temperature fluctuations are the strongest between the two magnetic islands.A statistical analysis of high βN discharges operating with the reversed magnetic shear configuration in the EAST 2015-2018 campaign revealed the existence of the DTM in many discharges.During the DTM phase,all βN are reduced by 10%-30% within 0.1 s.However,there are two different βN behaviors thereafter-with and without βN recovery.Studying the physical mechanism of βN recovery during the DTM phase will benefit steady-state operation with reversed shear configurations in the future.     

Feasibility of applying the lower cut-off frequency for the density radial coverage extension in EAST reflectometry measurement

The extraordinary mode (X-mode) lower cut-off frequency is proposed for use in the reflectometry diagnostic on ITER for the electron density profile measurement, which is a trade-off between extreme plasma parameters and the accessible probing frequency. In contemporary experiments, the lower cut-off frequency can be identified at the probing frequency below the electron cyclotron frequency (fce) under certain plasma conditions. We provide here, for the first time, the experimental validation of the use of the lower cut-off frequency for the density profiles via the reflectometry measurement on EAST. The corresponding group delay of the lower cut-off frequency evolves continuously with the upper one, revealing a reasonable radial coverage extension of reflectometry measurement toward the plasma core. It is concluded that the lower cut-off frequency can be used as a supplement to the upper one in the density profile inversion process, which is of particular interest in the high magnetic field and/or density discharge to extend the radial coverage of reflectometry measurement.