BackgroundDuring operation, the Experimental Advanced Superconducting Tokamak (EAST) device requires precise diagnosis of fast ion distribution functions, which is a critical requirement for conducting plasma physics research and ensuring stable operation of the device.PurposeThis study aims to meet the diagnostic requirements for fast ion distribution functions in the EAST device, and thus designs an electric field-parallel neutral particle analyzer (E∥B NPA) to achieve precise diagnostics of fast ions, hence to meet the diagnostic requirements for fast ion distribution functions in the EAST device.MethodsThe core work focused on three key areas. Firstly, permanent magnet structure optimization for a permanent magnet system was constructed using low-carbon steel magnetic yoke, NdFeB permanent magnets, and specially configured magnetic poles. Uniform thickness design was applied to the magnetic yoke to mitigate magnetic flux bottlenecks and saturation risks, while a zigzag-shaped air gap with shorter straight segments was selected to enhance ion deflection capability. Subsequently, the distribution of magnetic induction intensity within the magnetic gap was simulated and calculated using COMSOL software. Then, an electrostatic deflector with 16 mm spacing, 12 kV voltage, and a 7° tilt angle for the lower plate was integrated to optimize the electric field profile. Finally, magnetic shielding for the detection unit: magnetic shielding for the detection unit was implemented through a photomultiplier tube (PMT) array with an innovative grid-pattern magnetic shielding structure.ResultsThe calculation results show that both the volume and weight of the optimized magnet are reduced, the electrostatic deflector precisely separates particles into upper, middle, and lower rows whilst the magnetic shielding capability of the grid-like magnetic shielding structure exceeds the International Thermonuclear Experimental Reactor (ITER) design by 37%. Simulation verification results demonstrate that this designed E∥B NPA can measure hydrogen (30~440 keV), deuterium (15~220 keV), and tritium (10~143 keV) across their respective energy ranges through charged particle trajectory.ConclusionsThe E∥B NPA proposed in this study has successfully achieved mass-resolved fast ion spectrum diagnostics, effectively meeting the diagnostic requirements for fast ion distribution functions in the EAST device.
ZHU et al. (Sun,) studied this question.