**Acknowledgements**

This work is supported by the National Special Magnetic Confinement Fusion Energy Research of China (No. 2015GB108001B), the National Natural Science Foundation of China (No. 11675155, 91226104), and the National Key Research and Development Program of China (No. 2016YFA0401603). The author wishes to acknowledge all participators of the projects, including Dr. Yiwei Yang, Dr. Lei Zheng, Dr. Song Feng, MS. Caifeng Lai, Prof. Xinxin Lu, MS. Zhujun Liu, Prof. Li Jiang, Prof. Mei Wang, MS. Zijie Han, et al. All participators would like to thank Prof. Benchao Lou and his group for operating the neutron generator. The author thanks the reviewers, comments and suggestion.
