Simulation analysis of fast electron response of ZnS(Ag) scintillator in EAST

Abstract

BackgroundIn a tokamak, when fast electrons are deconfined by the tokamak magnetic field constraint and lost to the vacuum wall or limiter, the device may become damaged and the discharge may be affected.PurposeThis study aims to explore the loss behavior of fast electrons during discharge using a diagnostic system based on a ZnS(Ag) scintillator probe for detecting the loss of fast electrons on the Experimental Advanced Superconducting Tokamak (EAST).MethodsThe Geant4 simulation program was employed to simulate the interaction between electrons in different initial states and the scintillator probe of the diagnostic system. Firstly, the probe model and the filling material model of stainless steel and ZnS(Ag) coating were established in Geant4. Then, the interaction between electron beam and scintillator probe under different incident conditions (incident energy, angle, scintillator thickness, magnetic field size, etc.) were simulated, and the physical processes were recorded. Finally, the recorded data were accessed by MATLAB programming for analysis.ResultsThe results show that the contribution of secondary electrons and initial electrons to the luminescence intensity of scintillators occupies different dominant energy ranges. The luminescence intensity first increases and then decreases with the increase of incident electron energy, with a peak value around 12 MeV, and the number of emitted photons at oblique incidence is greater than that at vertical incidence. When the electron energy is lower than 4.3 MeV, secondary particles dominate the scintillation, and when the electron energy is higher than 4.3 MeV, primary particles dominate. The thickness of the scintillator has no significant effect on the peak position. After, the luminous intensity is considerably affected by the magnetic field angle and electron pitch angle after adding a magnetic field.ConclusionsThe results of this study contribute to the understanding of the fast electron loss signal detected by the scintillator probe in the EAST experiments, providing a basis for further study of fast electron loss.

Keywords

• tokamak
• scintillator
• geant4
• fast electron