HL-2A和HL-2M托卡马克中子产额标定研究

Fusion power is the ultimate goal of fusion research. Fusion power, neutron yield, measurements on Tokamak devices have played a more and more important role for providing information on plasma parameters and confinement properties. It is essential to calibrate detection efficiency of neutron flux detector for neutron yield measurement. The neutron yield calibration has been completed in several Tokamaks, such as JET, TFTR JT-60U，however it is still in the blank in our country. HL-2A Tokamak first achieve H-mode in our country. Under this condition, fusion neutron yield increase substantially as a result of neutral beam heating. Fusion neutron yield calibration is brooked no delay. We have established MCNP model of HL-2A host and hall. A preliminary analysis of Effect of the source spectrum, spatial distribution on the calibration results, relationship between the toroidal distribution of calibration source and detector efficiency, as well as effect of the detector position on the detection efficiency was preliminarily analyzed. This research will improve the tokamak model, analyze the impact of the neutron source spectrum, spatial distribution, the detector calibration position, optimize the calibration solution, implement the in-situ calibration for HL-2A Tokamak and determine the calibration results and error. Then this research also will carry out in-situ calibration on HL-2A Tokamak and determine the calibration results and error while HL-2M Tokamak being built.

聚变功率输出是聚变研究的终极目标，聚变功率即聚变中子产额的准确测量离不开精确的标定。国际上已经进行了大功率聚变实验的托卡马克装置均进行了中子产额标定，确定了中子通量探测器的探测效率，而国内这方面的研究还处于空白。HL-2A托卡马克在国内第一个实现高约束模式运行，同时伴随着中性束加热功率的增加，聚变中子产额大幅度增加，使聚变中子产额标定提上了日程。我们已经建立HL-2A主机和大厅的MCNP模型，初步分析了源能谱、空间分布对标定结果的影响，探测器效率与标定源环向分布的关系，以及探测器位置对探测效率的影响。此研究将完善托卡马克模型，详细分析中子源能谱、空间分布、探测器位置对标定实验的影响，优化现场标定方案；在HL-2A托卡马克进行现场标定实验，确定标定结果和误差。然后在建成的HL-2M托卡马克上，进行标定实验确定标定结果和误差。

聚变功率输出是聚变研究的终极目标，聚变功率的测量需要精确的标定来确定。本研究以我国HL-2A/2M两个中大型托卡马克的聚变功率和中子产额的标定为目标进行了多项研究。首先建立托卡马克中子学模型，分析了托卡马克实验时中子的通量分布，优化确定了中子通量探测器的布置，通过合理的慢化剂设计降低了中子能谱变化对探测效率的影响，得出了各种探测器的探测效率。然后为裂变室探测器研制了专用的前置放大器和成形系统，降低了本底电流噪声对测量的影响，提高了模拟放大系统的频率。建立了高效率的氦3计数管中子探测系统，研制了信号成形放大器，进行了谱形状分析和信号收集时间分析，分析了磁场的分布和影响，设计了磁屏蔽和探测器支撑结构。最终根据分析结果和调研结果，确定了标定方案，使用产额大于每秒一千万中子的锎252作为标定源，进行了标定实验，在HL-2A装置环向十六个位置测量了探测器的效率，确定了裂变室探测器和氦3计数管的探测效率；在HL-2M装置四个环向位置测量氦3计数管的探测效率。估计和分析误差来源项：中子源强度测量误差，中子能谱差异引起的误差，以及统计误差，确定标定结果的不确定度。通过两个装置中子产额的标定研究，进一步掌握了托卡马克中子学分析方法，丰富了中子通量诊断的手段，积累了中子产额标定的经验，为将来的聚变实验堆中子产额和聚变功率标定打下了基础。