Fig. 1. Schematic of GCD structure and physical process

Fig. 2. Schematic of GCD measurement signal timing

Fig. 3. Simulated electron conversion efficiency for various convertor materials

Fig. 4. Simulated electron conversion efficiency for different thickness of C convertor

Fig. 5. Dependence of collected Cherenkov photon amount arrived at the end of gas cell on the gas length and gas diameter at a 6 MeV threshold energy. (a) Gas length; (b) gas diameter

Fig. 6. Simulation radial X/Y distribution of Cherenkov photons at different Z-positions along the axial direction of gas cell. (a) Z=5 cm; (b) Z=30 cm; (c) Z=55 cm; (d) Z=80 cm

Fig. 7. Normalized angular distribution of Cherenkov photons in each statistic unit along the axial direction of gas cell

Fig. 8. Normalized collection photon amount Nph and signal frontier ratio χ as functions of secondary mirror curvature R2 under different primary mirror curvature R1

Fig. 9. Comparison of collecting photon waveforms under two optimized parameters

Fig. 10. Simulation radial distribution of Cherenkov photons at the position of secondary mirror before and after reflection by primary mirror. (a) Before reflection by primary mirror; (b) after reflection by primary mirror

Fig. 11. Time interval tdelay between precursor signal and main signal,and normalized collection photon amount Nph as functions of the distance L1 between secondary mirror and primary mirror

Fig. 12. Simulation results of collecting photon time waveforms before and after adding tungsten shield

Fig. 13. Simulated angular distribution of collected Cherenkov photons

Fig. 14. Simulated measurement signal by forward calculation method when electron threshold energy Eth is 6 MeV, neutron yield Yn is 10¹³,and photo multiplier tube gain M is 5×10³

Fig. 15. Dependence of detector sensitivity Sic and electron threshold energy Eth on CO₂ pressure

Fig. 16. Dependence of detector sensitivity Sic and system efficiency Sef on installation distance