Andong Xu, Yunhe Li, Tao Yu, Jiayi Zhang, Mingyuan Xu, Chenyu Pan, 郝宝龙, Yongqiang Zhang, Zishi Liu, Xutao 栩涛 XU 徐, Ziyu Wang, Yubo Zhang, Massimo Nocente, G. Gorini, Marco Tardocchi, Xiangqing Li, Juan Huang, Liqun Hu, Wei Zhang, X. J. Zhang, Guoqiang Zhong, Tieshuan Fan, Baonian Wan, The EAST Team
Abstract We present the first comprehensive multi-sightline neutron spectrometry measurements during synergistic NBI and deuterium third-harmonic ICRF heating on EAST. Using the time-of-flight enhanced diagnostic (TOFED) and three compact organic scintillator spectrometers, we observed a significant broadening in the measured spectra, indicating the acceleration of fast ions well beyond the injection energy. TRANSP simulations reveal a fast ion distribution extending to approximately 600 keV with a marked pitch-angle asymmetry favoring co-current velocities. These simulations are validated by synthetic spectra generated via the GENESIS code and the spectrometers’ instrumental response functions, which show excellent agreement with measurements. Furthermore, a TRANSP-independent weight-function analysis of the spectral cutoffs confirms the pitch asymmetry of the energetic tail. Orbit-topology calculations using the Orbit Weight Computational Framework (OWCF) demonstrate that this asymmetry is determined by the fast ion loss boundaries on EAST. These results establish the capability of multi-sightline neutron spectrometry to unveil the phase-space distribution of radiofrequency-accelerated ions, serving as a vital diagnostic for MeV-range fast ion physics relevant to future burning plasma research.